lessonID
stringlengths 6
6
| lessonName
stringlengths 3
52
| ID
stringlengths 6
21
| content
stringlengths 10
6.57k
| media_type
stringclasses 2
values | path
stringlengths 28
76
⌀ |
|---|---|---|---|---|---|
L_0868 | electric circuits | T_4342 | When a contractor builds a new home, she uses a set of plans called blueprints that show her how to build the house. The blueprints include circuit diagrams. The diagrams show how the wiring and other electrical components are to be installed in order to supply current to appliances, lights, and other electric devices. You can see an example of a very simple circuit in the Figure 1.2. Different parts of the circuit are represented by standard circuit symbols. An ammeter measures the flow of current through the circuit, and a voltmeter measures the voltage. A resistor is any device that converts some of the electricity to other forms of energy. For example, a resistor might be a light bulb or doorbell. A: The battery symbol (or a symbol for some other voltage source) must be included in every circuit. Without a source of voltage, there is no electric current. | text | null |
L_0869 | electric conductors and insulators | T_4343 | Electrical energy is transmitted by moving electrons in an electric current. In order to travel, electric current needs matter. It cannot pass through empty space. However, matter resists the flow of electric current. Thats because flowing electrons in current collide with particles of matter, which absorb their energy. Some types of matter offer more or less resistance to electric current than others. | text | null |
L_0869 | electric conductors and insulators | T_4344 | Materials that have low resistance to electric current are called electric conductors. Many metalsincluding copper, aluminum, and steelare good conductors of electricity. The outer electrons of metal atoms are loosely bound and free to move, allowing electric current to flow. Water that has even a tiny amount of impurities is an electric conductor as well. Q: What do you think lightning rods are made of? A: Lightning rods are made of metal, usually copper or aluminum, both of which are excellent conductors of electricity. | text | null |
L_0869 | electric conductors and insulators | T_4345 | Materials that have high resistance to electric current are called electric insulators. Examples include most non- metallic solids, such as wood, rubber, and plastic. Their atoms hold onto their electrons tightly, so electric current cannot flow freely through them. Dry air is also an electric insulator. Q: You may have heard that rubber-soled shoes will protect you if you are struck by lightning. Do you think this is true? Why or why not? A: It isnt true. Rubber is an electric insulator, but a half-inch layer on the bottom of a pair of shoes is insignificant when it comes to lightning. The average lightning bolt has 100 million volts and can burn through any insulator, even the insulators on high-voltage power lines. | text | null |
L_0869 | electric conductors and insulators | T_4346 | Look at the electric wires in the Figure 1.1. They are made of copper and coated with plastic. Copper is very good conductor, and plastic is a very good insulator. When more than one material is available for electric current to flow through, the current always travels through the material with the least resistance. Thats why all the current passes through the copper wire and none flows through its plastic coating. | text | null |
L_0870 | electric current | T_4347 | Electric current is a continuous flow of electric charges (electrons). Current is measured as the amount of charge that flows past a given point in a certain amount of time. The SI unit for electric current is the ampere (A), or amp. Electric current may flow in just one direction (direct current), or it may keep reversing direction (alternating current). Q: Why do you think charges flow in an electric current? A: Electric charges flow when they have electric potential energy. Potential energy is stored energy that an object has due to its position or shape. | text | null |
L_0870 | electric current | T_4348 | Electric potential energy comes from the position of a charged particle in an electric field. For example, when two negative charges are close together, they have potential energy because they repel each other and have the potential to push apart. If the charges actually move apart, their potential energy decreases. Electric charges always move spontaneously from a position where they have higher potential energy to a position where they have lower potential energy. This is like water falling over a dam from an area of higher to lower potential energy due to gravity. | text | null |
L_0870 | electric current | T_4349 | For an electric charge to move from one position to another, there must be a difference in electric potential energy between the two positions. A difference in electric potential energy is called voltage. The SI unit for voltage is the volt (V). Look at the Figure 1.1. It shows a simple circuit. The source of voltage in the circuit is a 1.5-volt battery. The difference of 1.5 volts between the two battery terminals results in a spontaneous flow of charges, or electric current, between them. Notice that the current flows from the negative terminal to the positive terminal, because electric current is a flow of electrons. Q: You might put a 1.5-volt battery in a TV remote. The battery in a car is a 12-volt battery. How do you think the current of a 12-volt battery compares to the current of a 1.5-volt battery? A: Greater voltage means a greater difference in potential energy, so the 12-volt battery can produce more current than the 1.5-volt battery. | text | null |
L_0871 | electric fields | T_4350 | An electric field is a space around a charged particle where the particle exerts electric force on other charged particles. Because of their force fields, charged particles can exert force on each other without actually touching. Electric fields are generally represented by arrows, as you can see in the Figure 1.1. The arrows show the direction of electric force around a positive particle and a negative particle. | text | null |
L_0871 | electric fields | T_4351 | When charged particles are close enough to exert force on each other, their electric fields interact. This is illustrated in the Figure 1.2. The lines of force bend together when particles with different charges attract each other. The lines bend apart when particles with like charges repel each other. Q: What would the lines of force look like around two negative particles? A: They would look like the lines around two positive particles, except the arrows would point toward, rather than away from, the negative particles. | text | null |
L_0871 | electric fields | T_4351 | When charged particles are close enough to exert force on each other, their electric fields interact. This is illustrated in the Figure 1.2. The lines of force bend together when particles with different charges attract each other. The lines bend apart when particles with like charges repel each other. Q: What would the lines of force look like around two negative particles? A: They would look like the lines around two positive particles, except the arrows would point toward, rather than away from, the negative particles. | text | null |
L_0872 | electric generators | T_4352 | You have already learned about the physical properties of matter. You may recall that physical properties can be measured and observed. You are able to use your senses to observe and measure them. You can easily tell if something is a certain color. You can tell what state it is in, whether solid, liquid, or gas. You can run tests to see if it conducts electricity. Also, physical changes occur without matter becoming something else. If you tear a piece of paper, each piece is still paper. Do you think this holds true for chemical properties? Chemical properties can also be measured or observed. This is where the similarity ends. You can only see chemical properties when matter undergoes a change. This change results in an entirely different kind of matter. For example, the ability of iron to rust can only be observed after it rusts. The shiny piece of metal gives no clue to whether it will rust or not until it does. But what is rust? When iron rusts, it combines with oxygen. Iron and oxygen is new substance, called iron oxide. It is no longer just iron. It has undergone a change. It is now a different substance. Iron is very hard and silver in color. In contrast, iron oxide is flakey and reddish brown. The ability to rust is only one type of chemical property. | text | null |
L_0872 | electric generators | T_4353 | Reactivity is another type of chemical property. Reactivity is the ability of matter to combine chemically with other substances. Some kinds of matter are extremely reactive. Others kinds of matter are extremely unreactive. Have you ever mixed baking soda with vinegar in your science class? If you have, you have seen an interesting reaction. Please do not try this at home without supervision. Vinegar and baking soda both have the chemical property that causes them to react with each other. Other substances are very unreactive. | text | null |
L_0872 | electric generators | T_4354 | Have you ever seen a symbol that says "Flammable"? You might see such a symbol on a gasoline can. Gasoline is highly flammable. That is why there are signs at the gas station that say, "NO SMOKING." Flammability is the ability of matter to burn. When matter burns, it combines with oxygen. When it does, it changes to different substances. Wood is an example of flammable matter, as seen in Figure 1.1. Q: How can you tell that wood ashes are a different substance than wood? A: Ashes have different properties than wood. For example, ashes are gray and powdery. Wood is brown and hard. Q: What are some other substances that have the property of flammability? A: Substances called fuels have the property of flammability. They include fossil fuels such as coal, natural gas, and petroleum. For example, gasoline is used in our cars because it is flammable. This property enables car engines to run. Substances made of wood, such as paper and cardboard, are also flammable. | text | null |
L_0872 | electric generators | T_4355 | 1. What is a chemical property? 2. Define the chemical property called reactivity. 3. What is flammability? Identify examples of flammable matter. | text | null |
L_0873 | electric power and electrical energy use | T_4356 | The rate at which a device changes electric current to another form of energy is called electric power. The SI unit for powerincluding electric poweris the watt. A watt equals 1 joule of energy per second. High wattages are often expressed in kilowatts, where 1 kilowatt equals 1000 watts. The power of an electric device, such as a hair dryer, can be calculated if you know the voltage of the circuit and how much current the device receives. The following equation is used: Power (watts) = Current (amps) Voltage (volts) Assume that Mirandas hair dryer is the only electric device in a 120-volt circuit that carries 15 amps of current. Then the power of her hair dryer in kilowatts is: Power = 15 amps 120 volts = 1800 watts, or 1.8 kilowatts Q: If a different hair dryer is plugged into a 120-volt circuit that carries 10 amps of current. What is the power of the other hair dryer? A: Substitute these values in the power equation: Power = 10 amps 120 volts = 1200 watts, or 1.2 kilowatts | text | null |
L_0873 | electric power and electrical energy use | T_4357 | Did you ever wonder how much electrical energy it takes to use an appliance such as a hair dryer? Electrical energy use depends on the power of the appliance and how long it is used. It can be calculated with this equation: Electrical Energy = Power Time If Miranda uses her 1.8-kilowatt hair dryer for 0.2 hours, how much electrical energy does she use? Electrical Energy = 1.8 kilowatts 0.2 hours = 0.36 kilowatt-hours Electrical energy use is typically expressed in kilowatt-hours, as in this example. How much energy is this? One kilowatt-hour equals 3.6 million joules of energy. Q: Suppose Miranda were to use a 1.2-kilowatt hair dryer for 0.2 hours. How much electrical energy would she use then? A: She would use: Electrical Energy = 1.2 kilowatts 0.2 hour = 0.24 kilowatt-hours | text | null |
L_0874 | electric resistance | T_4358 | In physics, resistance is opposition to the flow of electric charges in an electric current as it travels through matter. The SI unit for resistance is the ohm. Resistance occurs because moving electrons in current bump into atoms of matter. Resistance reduces the amount of electrical energy that is transferred through matter. Thats because some of the electrical energy is absorbed by the atoms and changed to other forms of energy, such as heat. Q: In the rugby analogy to resistance in physics, what do the players on each team represent? A: The player on the blue and black team represents a moving electron in an electric current. The players on the red and blue team represent particles of matter through which the current is flowing. | text | null |
L_0874 | electric resistance | T_4359 | How much resistance a material has depends on several factors: the type of material, its width, its length, and its temperature. All materials have some resistance, but certain materials resist the flow of electric current more or less than other materials do. Materials such as plastics have high resistance to electric current. They are called electric insulators. Materials such as metals have low resistance to electric current. They are called electric conductors. A wide wire has less resistance than a narrow wire of the same material. Electricity flowing through a wire is like water flowing through a hose. More water can flow through a wide hose than a narrow hose. In a similar way, more current can flow through a wide wire than a narrow wire. A longer wire has more resistance than a shorter wire. Current must travel farther through a longer wire, so there are more chances for it to collide with particles of matter. A cooler wire has less resistance than a warmer wire. Cooler particles have less kinetic energy, so they move more slowly. Therefore, they are less likely to collide with moving electrons in current. Materials called superconductors have virtually no resistance when they are cooled to extremely low temperatures. | text | null |
L_0874 | electric resistance | T_4360 | Resistance can be helpful or just a drain on electrical energy. If the aim is to transmit electric current through a wire from one place to another, then resistance is a drawback. It reduces the amount of electrical energy that is transmitted because some of the current is absorbed by particles of matter. On the other hand, if the aim is to use electricity to produce heat or light, then resistance is useful. When particles of matter absorb electrical energy, they change it to heat or light. For example, when electric current flows through the tungsten wire inside an incandescent light bulb like the one in the Figure 1.1, the tungsten resists the flow of electric charge. It absorbs electrical energy and converts some of it to light and heat. Q: The tungsten wire inside a light bulb is extremely thin. How does this help it do its job? A: The extremely thin wire has more resistance than a wider wire would. This helps the wire resist electric current and change it to light. | text | null |
L_0875 | electric safety | T_4361 | Did you ever see an old appliance with a damaged cord, like the old shown in the Figure 1.1? A damaged electric cord can cause a severe shock if it allows current to pass from the cord to a person who touches it. A damaged cord can also cause a short circuit. A short circuit occurs when electric current follows a shorter path than the intended loop of the circuit. An electric cord contains two wires: one that carries current from the outlet to the appliance and one that carries current from the appliance back to the outlet. If the two wires in a damaged cord come into contact with each other, current flows from one wire to the other and bypasses the appliance. This may cause the wires to overheat and start a fire. | text | null |
L_0875 | electric safety | T_4362 | Because electricity can be so dangerous, safety features are built into modern electric circuits and devices. They include three-prong plugs, circuit breakers, and GFCI outlets. You can read about these three safety features in the Figure 1.2. GFCI Outlet: GFCI stands for ground- fault circuit interrupter. GFCI outlets are typically found in bathrooms and kitchens where the use of water poses a risk of shock (because water is a good electric conductor). A GFCI outlet contains a device that monitors the amount of current leaving and returning to the outlet. If less current is returning than leaving, this means that current is escaping. When this occurs, a tiny circuit breaker in the outlet interrupts the circuit. The breaker can be reset by pushing a button on the outlet cover. Q: Can you think of any other electric safety features? A: One safety feature is the label on a lamp that warns the user of the maximum safe wattage for light bulbs. Another safety feature is double insulation on many electric devices. Not only are the electric wires insulated with a coating | text | null |
L_0875 | electric safety | T_4363 | Even with electric safety features, electricity is still dangerous if it is misused. Follow the safety rules below to reduce the risk of injury or fire from electricity. Never mix electricity and water. Dont plug in or turn on electric lights or appliances when your hands are wet, you are standing in water, or you are in the shower or bathtub. The current could flow through the waterand youbecause water is a good conductor of electricity. Never overload circuits. Avoid plugging too many devices into one outlet or extension cord. The more devices that are plugged in, the more current the circuit carries. Too much current can overheat a circuit and start a fire. Never use devices with damaged cords or plugs. They can cause shocks, shorts, and fires. Never put anything except plugs into electric outlets. Putting any other object into an outlet is likely to cause a serious shock that could be fatal. Never go near fallen electric lines. They could have very high voltage. Report fallen lines to the electric company as soon as possible. | text | null |
L_0876 | electric transformers | T_4364 | An electric transformer is a device that uses electromagnetic induction to change the voltage of electric current. Electromagnetic induction is the process of generating current with a magnetic field. It occurs when a magnetic field and electric conductor, such as a coil of wire, move relative to one another. A transformer may either increase or decrease voltage. You can see the basic components of an electric transformer in the Figure 1.1. Click image to the left or use the URL below. URL: The transformer in the diagram consists of two wire coils wrapped around an iron core. Each coil is part of a different circuit. When alternating current passes through coil P, it magnetizes the iron core. Because the current is alternating, the magnetic field of the iron core keeps reversing. This is where electromagnetic induction comes in. The changing magnetic field induces alternating current in coil S of the other circuit. | text | null |
L_0876 | electric transformers | T_4365 | Notice that coil P and coil S in the Figure 1.1 have the same number of turns of wire. In this case, the voltages of the primary and secondary currents are the same. Usually, the two coils of a transformer have different numbers of turns. In that case, the voltages of the two currents are different. When coil S has more turns than coil P, the voltage in the secondary current is greater than the voltage in the primary current (see Figure 1.2). This type of transformer is called a step-up transformer. Thats because it steps up, or increases, the voltage. When coil S has fewer turns of wire than coil P, the voltage in the secondary current is less than the voltage in the primary current (see Figure 1.3). This type of transformer is called a step-down transformer because it steps down, or decreases, the voltage. Q: Both step-up and step-down transformers are used in the electrical grid that carries electricity from a power plant to your home. Where in the grid do you think step-down transformers might be used? A: One place that step-down transformers are used is on the electric poles that supply current to homes. They reduce the voltage of the electric current before it enters home circuits. | text | null |
L_0876 | electric transformers | T_4365 | Notice that coil P and coil S in the Figure 1.1 have the same number of turns of wire. In this case, the voltages of the primary and secondary currents are the same. Usually, the two coils of a transformer have different numbers of turns. In that case, the voltages of the two currents are different. When coil S has more turns than coil P, the voltage in the secondary current is greater than the voltage in the primary current (see Figure 1.2). This type of transformer is called a step-up transformer. Thats because it steps up, or increases, the voltage. When coil S has fewer turns of wire than coil P, the voltage in the secondary current is less than the voltage in the primary current (see Figure 1.3). This type of transformer is called a step-down transformer because it steps down, or decreases, the voltage. Q: Both step-up and step-down transformers are used in the electrical grid that carries electricity from a power plant to your home. Where in the grid do you think step-down transformers might be used? A: One place that step-down transformers are used is on the electric poles that supply current to homes. They reduce the voltage of the electric current before it enters home circuits. | text | null |
L_0877 | electrical grid | T_4366 | An electrical grid is the entire electrical system that generates, transmits, and distributes electric power throughout a region or country. A very simple electrical grid is sketched in the Figure 1.1. The grid includes a power plant, transmission lines, and electric substations, all of which work together to provide alternating current to customers. | text | null |
L_0877 | electrical grid | T_4367 | Electricity originates in power plants. They have electric generators that produce electricity by electromagnetic induction. In this process, a changing magnetic field is used to generate electric current. The generators convert kinetic energy to electrical energy. The kinetic energy may come from flowing water, burning fuel, wind, or some other energy source. | text | null |
L_0877 | electrical grid | T_4368 | Transmission lines on big towerslike those in the opening photo abovecarry high-voltage electric current from power plants to electric substations. Smaller towers and individual power poles carry lower-voltage current from electric substations to homes and businesses. | text | null |
L_0877 | electrical grid | T_4369 | Electric substations have several functions. Many substations distribute electricity from a few high-voltage lines to several lower-voltage lines. They have electric transformers, which use electromagnetic induction to change the voltage of the current. Some transformers increase the voltage; others decrease the voltage. In the Figure 1.2, you can see how both types of transformers are used in an electrical grid. A step-up transformer increases the voltage of the current as it leaves the power plant. After the voltage has been increased, less current travels through the high-voltage power lines. This reduces the amount of power that is lost due to resistance of the power lines. A step-down transformer decreases the voltage of the current so it can be distributed safely to businesses and homes. A high-voltage power line may have 750,000 volts, whereas most home circuits have a maximum of 240 volts. Therefore, one or more step-down transformers are needed to decrease the voltage of current before it enters homes. Q: Assume that a home needs a 14-volt circuit for a light and a 120-volt circuit for a microwave oven. If the main power line entering home has 240 volts, what can you infer about the homes electrical system? A: The homes electrical system must have step-down transformers that lower the voltage for some of the homes circuits. | text | null |
L_0878 | electromagnet | T_4370 | An electromagnet is a solenoid wrapped around a bar of iron or other ferromagnetic material. A solenoid is a coil of wire with electric current flowing through it. This gives the coil north and south magnetic poles and a magnetic field. The magnetic field of the solenoid magnetizes the iron bar by aligning its magnetic domains. You can see this in the Figure 1.1. | text | null |
L_0878 | electromagnet | T_4371 | The combined magnetic force of the magnetized wire coil and iron bar makes an electromagnet very strong. In fact, electromagnets are the strongest magnets made. An electromagnet is stronger if there are more turns in the coil of wire or there is more current flowing through it. A bigger bar or one made of material that is easier to magnetize also increases an electromagnets strength. | text | null |
L_0878 | electromagnet | T_4372 | Besides their strength, another pro of electromagnets is the ability to control them by controlling the electric current. Turning the current on or off turns the magnetic field on or off. The amount of current flowing through the coil can also be changed to control the strength of the electromagnet. Q: Why might it be useful to be able to turn an electromagnet on and off? A: Look back at the electromagnet hanging from the crane in the opening photo. It is useful to turn on its magnetic field so it can pick up the metal car parts. It is also useful to turn off its magnetic field so it can drop the parts into the train car. | text | null |
L_0879 | electromagnetic devices | T_4373 | Many common electric devices contain electromagnets. An electromagnet is a coil of wire wrapped around a bar of iron or other ferromagnetic material. When electric current flows through the wire, it causes the coil and iron bar to become magnetized. An electromagnet has north and south magnetic poles and a magnetic field. Turning off the current turns off the electromagnet. To understand how electromagnets are used in electric devices, well focus on two common devices: doorbells and electric motors like the one that turns the blades of a fan. Q: Besides doorbells and fans, what are some other devices that contain electromagnets? A: Any device that has an electric motor contains electromagnets. Some other examples include hairdryers, CD players, power drills, electric saws, and electric mixers. | text | null |
L_0879 | electromagnetic devices | T_4374 | The Figure 1.1 represents a simple doorbell. Like most doorbells, it has a button located by the front door. Pressing the button causes two electric contacts to come together and complete an electric circuit. In other words, the button is a switch. The circuit is also connected to a source of current, an electromagnet, and a clapper that strikes a bell. What happens when current flows through the doorbell circuit? The electromagnet turns on, and its magnetic field attracts the clapper. This causes the clapper to hit the bell, making it ring. Because the clapper is part of the circuit, when it moves to strike the bell, it breaks the circuit. Without current flowing through the circuit, the electromagnet turns off, and the clapper returns to its original position. When the clapper moves back to its original position, this closes the circuit again and turns the electromagnet back on. The electromagnet again attracts the clapper, which hits the bell once more. This sequence of events keeps repeating. Q: How can you stop the sequence of events so the doorbell will stop ringing? A: Stop pressing the button! This interrupts the circuit so no current can flow through it. | text | null |
L_0879 | electromagnetic devices | T_4375 | An electric motor is a device that uses an electromagnet to change electrical energy to kinetic energy. You can see a simple diagram of an electric motor in the Figure 1.2. The motor contains an electromagnet that is connected to a shaft. When current flows through the motor, the electromagnet rotates, causing the shaft to rotate as well. The rotating shaft moves other parts of the device. For example, in an electric fan, the rotating shaft turns the blades of the fan. Why does the motors electromagnet rotate? The electromagnet is located between the north and south poles of two permanent magnets. When current flows through the electromagnet, it becomes magnetized, and its poles are repelled by the like poles of the permanent magnets. This causes the electromagnet to rotate toward the unlike poles of the permanent magnets. A device called a commutator then changes the direction of the current so the poles of the electromagnet are reversed. The reversed poles are again repelled by the poles of the permanent magnets, which have not reversed. This causes the electromagnet to continue to rotate. These events keep repeating, so the electromagnet rotates continuously. | text | null |
L_0880 | electromagnetic induction | T_4376 | Electromagnetic induction is the process of generating electric current with a magnetic field. It occurs whenever a magnetic field and an electric conductor, such as a coil of wire, move relative to one another. As long as the conductor is part of a closed circuit, current will flow through it whenever it crosses lines of force in the magnetic field. One way this can happen is illustrated in the Figure 1.1. The sketch shows a magnet moving through a wire coil. Q: What is another way that a coil of wire and magnet can move relative to one another and generate an electric current? A: The coil of wire could be moved back and forth over the magnet. | text | null |
L_0880 | electromagnetic induction | T_4377 | The device with the pointer in the Figure 1.1 is an ammeter. It measures the current that flows through the wire. The faster the magnet or coil moves, the greater the amount of current that is produced. If more turns were added to the coil or a stronger magnet were used, this would produce more current as well. The Figure 1.2 shows the direction of the current that is generated by a moving magnet. If the magnet is moved back and forth repeatedly, the current keeps changing direction. In other words, alternating current (AC) is produced. Alternating current is electric current that keeps reversing direction. | text | null |
L_0880 | electromagnetic induction | T_4377 | The device with the pointer in the Figure 1.1 is an ammeter. It measures the current that flows through the wire. The faster the magnet or coil moves, the greater the amount of current that is produced. If more turns were added to the coil or a stronger magnet were used, this would produce more current as well. The Figure 1.2 shows the direction of the current that is generated by a moving magnet. If the magnet is moved back and forth repeatedly, the current keeps changing direction. In other words, alternating current (AC) is produced. Alternating current is electric current that keeps reversing direction. | text | null |
L_0880 | electromagnetic induction | T_4378 | Two important devices depend on electromagnetic induction: electric generators and electric transformers. Both devices play critical roles in producing and regulating the electric current we depend on in our daily lives. Electric generators use electromagnetic induction to change kinetic energy to electrical energy. They produce electricity in power plants. Electric transformers use electromagnetic induction to change the voltage of electric current. Some transformers increase voltage and other decrease voltage. Q: How do you think the girl on the exercise bike in the opening photo is using electromagnetic induction? A: As she pedals the bike, the kinetic energy of the turning pedals is used to move a conductor through a magnetic field. This generates electric current by electromagnetic induction. | text | null |
L_0883 | electromagnetism | T_4387 | Electromagnetism is magnetism produced by an electric current. When electric current flows through a wire, it creates a magnetic field that surrounds the wire in circles. You can see this in the diagram below. Note that electric current is conventionally shown moving from positive to negative electric potential, as in this diagram. However, electrons in current actually flow in the opposite direction, from negative to positive potential. Q: If more current flows through a wire, how might this affect the magnetic field surrounding the wire? A: With more current, the magnetic field is stronger. | text | null |
L_0883 | electromagnetism | T_4388 | The direction of the magnetic field created when current flows through a wire depends on the direction of the current. A simple rule, called the right hand rule, makes it easy to find the direction of the magnetic field if the direction of the current is known. The rule is illustrated in the Figure 1.1. When the thumb of the right hand is pointing in the same direction as the current, the fingers of the right hand curl around the wire in the direction of the magnetic field. Click image to the left or use the URL below. URL: | text | null |
L_0883 | electromagnetism | T_4389 | Electromagnetism is used not only in a doorbells but in many other electric devices as well, such as electric motors and loudspeakers. It is also used to store information on computer disks. An important medical use of electromagnetism is magnetic resonance imaging (MRI). This is a technique for making images of the inside of the body in order to diagnose diseases or injuries. Magnetism created with electric current is so useful because it can be turned on or off simply by turning the current on or off. The strength of the magnetic field is also easy to control by changing the amount of current. You cant do either of these things with a regular magnet. | text | null |
L_0885 | electronic component | T_4393 | Electronic components are the parts used in electronic devices such as computers. The components change electric current so it can carry information. Types of electronic components include diodes, transistors, and integrated circuits, all of which you can read about below. However, to understand how these components work, you first need to know about semiconductors. Thats because electronic components consist of semiconductorssometimes millions of them! | text | null |
L_0885 | electronic component | T_4394 | A semiconductor is a solid crystal, consisting mainly of silicon. It gets its name from the fact that it can conduct current better than an electric insulator but not as well as an electric conductor. As you can see in the Figure 1.1, each silicon atom has four valence electrons that it shares with other silicon atoms in the crystal. A semiconductor is formed by replacing a few silicon atoms with other atoms, such as phosphorus or boron, which have more or less valence electrons than silicon. This is called doping, and its what allows the semiconductor to conduct electric current. Q: Why wouldnt a pure silicon crystal be able to conduct electric current? A: Electric current is a flow of electrons. All of the valence electrons of silicon atoms in a pure crystal are shared with other silicon atoms, so they are not free to move and carry current. There are two different types of semiconductors: n-type and p-type. An n-type (negative-type) semiconductor consists of silicon and an element such as phosphorus that gives the silicon crystal extra electrons. You can see this in the Figure 1.1. An n-type semiconductor is like the negative terminal of a battery. A p-type (positive-type) semiconductor consists of silicon and an element such as boron that gives the silicon positively charged holes where electrons are missing. This is also shown in the Figure 1.1. A p-type semiconductor is like the positive terminal of a battery. | text | null |
L_0885 | electronic component | T_4395 | A diode is an electronic component that consists of a p-type and an n-type semiconductor placed side by side, as shown in the Figure 1.2. When a diode is connected by leads to a source of voltage, electrons flow from the n-type to the p-type semiconductor. This is the only direction that electrons can flow in a diode. This makes a diode useful for changing alternating current to direct current. | text | null |
L_0885 | electronic component | T_4396 | A transistor consists of three semiconductors, either p-n-p or n-p-n. Both arrangements are illustrated in the Figure (through the base). Then a much larger current can flow through the transistor from end to end (from collector to emitter). This means that a transmitter can be used as a switch, with pulses of a small current turning a larger current on and off. A transistor can also be used to increase the amount of current flowing through a circuit. | text | null |
L_0885 | electronic component | T_4397 | An integrated circuitalso called a microchipis a tiny, flat piece of silicon that consists of layers of many electronic components such as transistors. You can see an integrated circuit in the Figure 1.4. Look how small it is compared with the finger its resting on. Although the integrated circuit is tiny, it may contain millions of smaller electronic components. Current flows extremely rapidly in an integrated circuit because it doesnt have far to travel. Integrated circuits are used in virtually all modern electronic devices to carry out specific tasks. | text | null |
L_0886 | electronic device | T_4398 | Many of the devices people commonly use today are electronic devices. Electronic devices use electric current to encode, analyze, or transmit information. In addition to computers, they include mobile phones, TV remotes, DVD and CD players, and digital cameras, to name just a few. Q: Can you think of other electronic devices that you use? A: Other examples include game systems and MP3 players. | text | null |
L_0886 | electronic device | T_4399 | Lets take a close look at the computer as an example of an electronic device. A computer contains integrated circuits, or microchips, that consist of millions of tiny electronic components. Information is encoded in digital electronic signals. Rapid pulses of voltage switch electric current on and off, producing long strings of 1s (current on) and 0s (current off). The 1s and 0s are the letters of the code, and a huge number of them are needed. One digit (either 0 or 1) is called a bit, which stands for binary digit. Each group of eight digits is called a byte, and a billion bytes is called a gigabyte. Because a computers circuits are so tiny and close together, the computer can be very fast and capable of many complex tasks while remaining small. The parts of a computer that transmit, process, or store digital signals are pictured and described in the Figure 1.1. They include the CPU, hard drive, ROM, and RAM. The motherboard ties all these parts of the computer together. The CPU, or central processing unit, carries out program instructions. The hard drive is a magnetic disc that provides long-term storage for programs and data. ROM (read-only memory) is a microchip that provides permanent storage. It stores important information such as start-up instructions. This memory remains even after the computer is turned off. RAM (random-access memory) is a microchip that temporarily stores programs and data that are currently being used. Anything stored in RAM is lost when the computer is turned off. The motherboard is connected to the CPU, hard drive, ROM, and RAM. It allows all these parts of the computer to receive power and communicate with one another. Q: Which part(s) of a computer are you using when you type a school report? A: You are using the RAM to store the word processing program and your document as you type it. You are using the CPU to carry out instructions in the word processing program, and you are probably using the hard drive to save your document. | text | null |
L_0887 | electronic signal | T_4400 | Electric devices, such as lights and household appliances, change electric current to other forms of energy. For example, an electric stove changes electric current to thermal energy. Other common devices, such as mobile phones and computers, use electric current for another purpose: to encode information. A message encoded this way is called an electronic signal, and the use of electric current for this purpose is called electronics. To encode a message with electric current, the voltage is changed rapidly, over and over again. Voltage is a difference in electric potential energy that is needed in order for electric current to flow. There are two different ways voltage can be changed, resulting in two different types of electronic signals, called analog signals and digital signals. | text | null |
L_0887 | electronic signal | T_4401 | Analog signals consist of continuously changing voltage in an electric circuit. The Figure 1.1 represents analog signals. These were the first electronic signals to be invented. They were used in early computers and other early electronic devices. Analog signals are subject to distortion and noise, so they arent used as often anymore. They are used mainly in microphones and some mobile phones to encode sounds as electronic signals. | text | null |
L_0887 | electronic signal | T_4402 | Today, most electronic signals are digital signals. Digital signals consist of rapid pulses of voltage that repeatedly switch the current off and on. The Figure 1.2 represents digital signals. This type of signal encodes information as a string of 0s (current off) and 1s (current on). This is called a binary (two-digit) code. The majority of modern electronic devices, including computers and many mobile phones, encode data as digital signals. Compared with analog signals, digital signals are easier to transmit and more accurate. | text | null |
L_0887 | electronic signal | T_4402 | Today, most electronic signals are digital signals. Digital signals consist of rapid pulses of voltage that repeatedly switch the current off and on. The Figure 1.2 represents digital signals. This type of signal encodes information as a string of 0s (current off) and 1s (current on). This is called a binary (two-digit) code. The majority of modern electronic devices, including computers and many mobile phones, encode data as digital signals. Compared with analog signals, digital signals are easier to transmit and more accurate. | text | null |
L_0896 | evaporation | T_4432 | Evaporation explains why clothes dry on a clothesline. Evaporation is the process in which a liquid changes to a gas without becoming hot enough to boil. It occurs when individual liquid particles at the exposed surface of the liquid absorb just enough energy to overcome the force of attraction with other liquid particles. If the surface particles are moving in the right direction, they will pull away from the liquid and move into the air. This is illustrated in the Figure 1.1. | text | null |
L_0896 | evaporation | T_4433 | Many factors influence how quickly a liquid evaporates. They include: temperature of the liquid. A cup of hot water will evaporate more quickly than a cup of cold water. exposed surface area of the liquid. The same amount of water will evaporate more quickly in a wide shallow bowl than in a tall narrow glass. presence or absence of other substances in the liquid. Pure water will evaporate more quickly than salt water. air movement. Clothes on a clothesline will dry more quickly on a windy day than on a still day. concentration of the evaporating substance in the air. Clothes will dry more quickly when air contains little water vapor. | text | null |
L_0896 | evaporation | T_4434 | Did you ever notice that moving air cools you down when youre hot and sweaty? For example, if you sit in front of a fan, you feel cooler. Thats because moving air helps to evaporate the sweat on your skin. But why does the evaporation of sweat cool you down? When a liquid such as sweat evaporates, energetic particles on the surface of the liquid escape into the air. After these particles leave, the remaining liquid has less energy, so it is cooler. This is called evaporative cooling. Q: On a hot day, high humidity makes you feel even hotter. Can you explain why? A: Humidity is a measure of the amount of water vapor in the air. When humidity is high, sweat evaporates more slowly because there is already a lot of water vapor in the air. The slower evaporation rate reduces the potential for evaporative cooling. | text | null |
L_0903 | freezing | T_4450 | You dont have to be an ice climber to enjoy ice. Skating and fishing are two other sports that are also done on ice. What is ice? Its simply water in the solid state. The process in which water or any other liquid changes to a solid is called freezing. Freezing occurs when a liquid cools to a point at which its particles no longer have enough energy to overcome the force of attraction between them. Instead, the particles remain in fixed positions, crowded closely together, as shown in the Figure 1.1. | text | null |
L_0903 | freezing | T_4451 | The temperature at which a substance freezes is known as its freezing point. Freezing point is a physical property of matter. The freezing point of pure water is 0 C. Below this temperature, water exists as ice. Above this temperature, it exists as liquid water or water vapor. Many other substances have much lower or higher freezing points than water. You can see some examples in the Table 1.1. The freezing point of pure water is included in the table for comparison. Substance Helium Oxygen Nitrogen Pure Water Lead Iron Carbon Freezing Point ( C) -272 -222 -210 0 328 1535 3500 Q: What trend do you see in this table? A: Substances in the table with freezing points lower than water are gases. Substances in the table with freezing points higher than water are solids. Q: Sodium is a solid at room temperature. Given this information, what can you infer about its freezing point? A: You can infer that the freezing point of sodium must be higher than room temperature, which is about 20 C. The freezing point of sodium is actually 98 C. | text | null |
L_0941 | liquids | T_4584 | Water is the most common substance on Earth, and most of it exists in the liquid state. A liquid is one of four well-known states of matter, along with solid, gas, and plasma states. The particles of liquids are in close contact with each other but not as tightly packed as the particles in solids. The particles can slip past one another and take the shape of their container. However, they cannot pull apart and spread out to take the volume of their container, as particles of a gas can. If the volume of a liquid is less than the volume of its container, the top surface of the liquid will be exposed to the air, like the vinegar in the bottle pictured in the Figure 1.1. Q: Why does most water on Earths surface exist in a liquid state? In what other states does water exist on Earth? A: Almost 97 percent of water on Earths surface is found as liquid salt water in the oceans. The temperature over most of Earths surface is above the freezing point (0 C) of water, so relatively little water exists as ice. Even near the poles, most of the water in the oceans is above the freezing point. And in very few places on Earths surface do temperatures reach the boiling point (100 C) of water. Although water exists in the atmosphere in a gaseous state, water vapor makes up less than 1 percent of Earths total water. | text | null |
L_0941 | liquids | T_4585 | Two unique properties of liquids are surface tension and viscosity. Surface tension is a force that pulls particles at the exposed surface of a liquid toward other liquid particles. Surface tension explains why water forms droplets, like the water droplet that has formed on the leaky faucet pictured in the Figure 1.2. Water drips from a leaky faucet. Viscosity is a liquids resistance to flowing. You can think of it as friction between particles of liquid. Thicker liquids are more viscous than thinner liquids. For example, the honey pictured in the Figure 1.3 is more viscous than the vinegar. Q: Which liquid do you think is more viscous: honey or chocolate syrup? | text | null |
L_0941 | liquids | T_4585 | Two unique properties of liquids are surface tension and viscosity. Surface tension is a force that pulls particles at the exposed surface of a liquid toward other liquid particles. Surface tension explains why water forms droplets, like the water droplet that has formed on the leaky faucet pictured in the Figure 1.2. Water drips from a leaky faucet. Viscosity is a liquids resistance to flowing. You can think of it as friction between particles of liquid. Thicker liquids are more viscous than thinner liquids. For example, the honey pictured in the Figure 1.3 is more viscous than the vinegar. Q: Which liquid do you think is more viscous: honey or chocolate syrup? | text | null |
L_0945 | matter mass and volume | T_4593 | Matter is all the stuff that exists in the universe. Everything you can see and touch is made of matter, including you! The only things that arent matter are forms of energy, such as light and sound. In science, matter is defined as anything that has mass and volume. Mass and volume measure different aspects of matter. | text | null |
L_0945 | matter mass and volume | T_4594 | Mass is a measure of the amount of matter in a substance or an object. The basic SI unit for mass is the kilogram (kg), but smaller masses may be measured in grams (g). To measure mass, you would use a balance. In the lab, mass may be measured with a triple beam balance or an electronic balance, but the old-fashioned balance pictured below may give you a better idea of what mass is. If both sides of this balance were at the same level, it would mean that the fruit in the left pan has the same mass as the iron object in the right pan. In that case, the fruit would have a mass of 1 kg, the same as the iron. As you can see, however, the fruit is at a higher level than the iron. This means that the fruit has less mass than the iron, that is, the fruits mass is less than 1 kg. Q: If the fruit were at a lower level than the iron object, what would be the mass of the fruit? A: The mass of the fruit would be greater than 1 kg. Mass is commonly confused with weight. The two are closely related, but they measure different things. Whereas mass measures the amount of matter in an object, weight measures the force of gravity acting on an object. The force of gravity on an object depends on its mass but also on the strength of gravity. If the strength of gravity is held constant (as it is all over Earth), then an object with a greater mass also has a greater weight. Q: With Earths gravity, an object with a mass of 1 kg has a weight of 2.2 lb. How much does a 10 kg object weigh on Earth? A: A 10 kg object weighs ten times as much as a 1 kg object: 10 2.2 lb = 22 lb | text | null |
L_0945 | matter mass and volume | T_4595 | Volume is a measure of the amount of space that a substance or an object takes up. The basic SI unit for volume is the cubic meter (m3 ), but smaller volumes may be measured in cm3 , and liquids may be measured in liters (L) or milliliters (mL). How the volume of matter is measured depends on its state. The volume of a liquid is measured with a measuring container, such as a measuring cup or graduated cylinder. The volume of a gas depends on the volume of its container: gases expand to fill whatever space is available to them. The volume of a regularly shaped solid can be calculated from its dimensions. For example, the volume of a rectangular solid is the product of its length, width, and height. The volume of an irregularly shaped solid can be measured by the displacement method. You can read below how this method works. Click image to the left or use the URL below. URL: Q: How could you find the volume of air in an otherwise empty room? A: If the room has a regular shape, you could calculate its volume from its dimensions. For example, the volume of a rectangular room can be calculated with the formula: Volume = length width height If the length of the room is 5.0 meters, the width is 3.0 meters, and the height is 2.5 meters, then the volume of the room is: Volume = 5.0 m 3.0 m 2.5 m = 37.5 m3 Q: What is the volume of the dinosaur in the diagram above? A: The volume of the water alone is 4.8 mL. The volume of the water and dinosaur together is 5.6 mL. Therefore, the volume of the dinosaur alone is 5.6 mL - 4.8 mL = 0.8 mL. | text | null |
L_0948 | melting | T_4603 | The process in which rocks or other solids change to liquids is called melting. Melting occurs when particles of a solid absorb enough energy to partly overcome the force of attraction holding them together. This allows them to move out of their fixed positions and slip over one another. Melting, like other changes of state, is a physical change in matter, so it doesnt change the chemical makeup or chemical properties of matter. Q: The molten rock that erupts from a volcano comes from deep underground. How is this related to its liquid state? A: It is always very hot deep underground where molten rock originates. The high temperatures give rock enough energy to melt and remain in a molten state. Underground rock in this state is called magma. Q: What happens to magma after it erupts and starts flowing over the surface of the ground? A: After magma erupts, it is called lava. On the surface, lava eventually cools and hardens to form solid rock. Other substances that are normally solids on Earth can also be heated until they melt. You can see an example in the Figure 1.1. The photo shows molten gold being poured into a mold. When the gold cools, it will harden into a solid gold bar that has the same shape as the mold. | text | null |
L_0948 | melting | T_4604 | The temperature at which a substance melts is called its melting point. Melting point is a physical property of matter. The gold pictured in the Figure 1.1, for example, has a melting point of 1064 C. This is a high melting point, and most other metals also have high melting points. The melting point of ice, in comparison, is much lower at 0 C. Many substances have even lower melting points. For example, the melting point of oxygen is -222 C. | text | null |
L_0948 | melting | T_4605 | Because of global climate change, temperatures all over Earth are rising. However, the melting points of Earths substances, including ice, are constant. The result? Glaciers are melting at an alarming rate. Melting glaciers cause rising sea levels and the risk of dangerous river flooding on land. Click image to the left or use the URL below. URL: | text | null |
L_0955 | mixtures | T_4625 | A mixture is a combination of two or more substances in any proportion. This is different from a compound, which consists of substances in fixed proportions. The substances in a mixture also do not combine chemically to form a new substance, as they do in a compound. Instead, they just intermingle and keep their original properties. The lemonade pictured above is a mixture because it doesnt have fixed proportions of ingredients. It could have more or less lemon juice, for example, or more or less sugar, and it would still be lemonade. Q: What are some other examples of mixtures? A: Other examples of liquid mixtures include salt water and salad dressing. Air is a mixture of gases, mainly nitrogen and oxygen. The rock pictured in the Figure 1.1 is a solid mixture. This rock is a mixture of smaller rocks and minerals. | text | null |
L_0955 | mixtures | T_4626 | The lemonade in the opening picture is an example of a homogeneous mixture. A homogeneous mixture has the same composition throughout. Another example of a homogeneous mixture is salt water. If you analyzed samples of ocean water in different places, you would find that the proportion of salt in each sample is the same: 3.5 percent. The rock in Figure 1.1 is an example of a heterogeneous mixture. A heterogeneous mixture varies in its composition. The black nuggets, for example, are not distributed evenly throughout the rock. | text | null |
L_0955 | mixtures | T_4627 | Mixtures have different properties depending on the size of their particles. Three types of mixtures based on particle size are solutions, suspensions, and colloids, all of which are described in Table 1.1. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: Type of Mixture Solutions Description A solution is a homogeneous mixture with tiny parti- cles. The particles are too small to see and also too small to settle or be filtered out of the mixture. When the salt is thoroughly mixed into the water in this glass, it will form a solution. The salt will no longer be visible in the water, and it wont settle to the bottom of the glass. Colloids A colloid is a homogeneous mixture with medium- sized particles. The particles are large enough to see but not large enough to settle or be filtered out of the mixture. The gelatin in this dish is a colloid. It looks red because you can see the red gelatin particles in the mixture. However, the particles are too small to settle to the bottom of the dish. A suspension is a heterogeneous mixture with large particles. The particles are large enough to see and also to settle or be filtered out of the mixture. The salad dressing in this bottle is a suspension. It contains oil, vinegar, herbs, and spices. If the bottle sits undisturbed for very long, the mixture will separate into its component parts. Thats why you should shake it before you use it. Suspensions Q: If you buy a can of paint at a paint store, a store employee may put the can on a shaker machine to mix up the paint in the can. What type of mixture is the paint? A: The paint is a suspension. Some of the components of the paint settle out of the mixture when it sits undisturbed for a long time. This explains why you need to shake (or stir) the paint before you use it. Q: The milk you buy in the supermarket has gone through a process called homogenization. This process breaks up the cream in the milk into smaller particles. As a result, the cream doesnt separate out of the milk no matter how long it sits on the shelf. Which type of mixture is homogenized milk? A: Homogenized milk is a colloid. The particles in the milk are large enough to seethats why milk is white instead of clear like water, which is the main component of milk. However, the particles are not large enough to settle out of the mixture. | text | null |
L_0955 | mixtures | T_4628 | The components of a mixture keep their own identity when they combine, so they retain their physical properties. Examples of physical properties include boiling point, ability to dissolve, and particle size. When components of mixtures vary in physical properties such as these, processes such as boiling, dissolving, or filtering can be used to separate them. Look at the Figure 1.2 of the Great Salt Lake in Utah. The water in the lake is a solution of salt and water. Do you see the white salt deposits near the shore? How did the salt separate from the salt water? Water has a lower boiling point than salt, and it evaporates in the heat of the sun. With its higher boiling point, the salt doesnt get hot enough to evaporate, so it is left behind. Q: Suppose you have a mixture of salt and pepper. What properties of the salt and pepper might allow you to separate them? A: Salt dissolves in water but pepper does not. If you mix salt and pepper with water, only the salt will dissolve, leaving the pepper floating in the water. You can separate the pepper from the water by pouring the mixture through a filter, such as a coffee filter. Q: After you separate the pepper from the salt water, how could you separate the salt from the water? A: You could heat the water until it boils and evaporates. The salt would be left behind. | text | null |
L_0975 | ohms law | T_4688 | For electric current to flow through a wire, there must be a source of voltage. Voltage is a difference in electric potential energy. As you might have guessed, greater voltage results in more current. As electric current flows through matter, particles of matter resist the moving charges. This is called resistance, and greater resistance results in less current. These relationships between electric current, voltage, and resistance were first demonstrated in the early 1800s by a German scientist named Georg Ohm, so they are referred to as Ohms law. Ohms law can be represented by the following equation. Current(amps) = Voltage(volts) Resistance(ohms) | text | null |
L_0975 | ohms law | T_4689 | Ohms law may be easier to understand with an analogy. Current flowing through a wire is like water flowing through a hose. Increasing voltage with a higher-volt battery increases the current. This is like opening the tap wider so more water flows through the hose. Increasing resistance reduces the current. This is like stepping on the hose so less water can flow through it. | text | null |
L_0975 | ohms law | T_4690 | You can use the equation for current (above) to calculate the amount of current flowing through a circuit when the voltage and resistance are known. Consider an electric wire that is connected to a 12-volt battery. If the wire has a resistance of 2 ohms, how much current is flowing through the wire? Current = 12 volts 2 ohms = 6 amps Q: If a 120-volt voltage source is connected to a wire with 10 ohms of resistance, how much current is flowing through the wire? A: Substitute these values into the equation for current: Current = 120 volts 10 ohms = 12 amps | text | null |
L_0981 | physical change | T_4709 | A physical change is a change in one or more physical properties of matter without any change in chemical properties. In other words, matter doesnt change into a different substance in a physical change. Examples of physical change include changes in the size or shape of matter. Changes of statefor example, from solid to liquid or from liquid to gasare also physical changes. Some of the processes that cause physical changes include cutting, bending, dissolving, freezing, boiling, and melting. Four examples of physical change are pictured in the Figure Click image to the left or use the URL below. URL: Q: In the Figure 1.1, what physical changes are occurring? A: The paper is being cut into smaller pieces, which is changing its size and shape. The ice cubes are turning into a puddle of liquid water because they are melting. This is a change of state. The tablet is disappearing in the glass of water because it is dissolving into particles that are too small to see. The lighthouse is becoming coated with ice as ocean spray freezes on its surface. This is another change of state. | text | null |
L_0981 | physical change | T_4710 | When matter undergoes physical change, it doesnt become a different substance. Therefore, physical changes are often easy to reverse. For example, when liquid water freezes to form ice, it can be changed back to liquid water by heating and melting the ice. Q: Salt dissolving in water is a physical change. How could this change be reversed? A: The salt water could be boiled until the water evaporates, leaving behind the salt. Water vapor from the boiling water could be captured and cooled. The water vapor would condense and change back to liquid water. | text | null |
L_0982 | physical properties of matter | T_4711 | Physical properties of matter are properties that can be measured or observed without matter changing to an entirely different substance. Physical properties are typically things you can detect with your senses. For example, they may be things that you can see, hear, smell, or feel. Q: What differences between snow and sand can you detect with your senses? A: You can see that snow and sand have a different color. You can also feel that snow is softer than sand. Both color and hardness are physical properties of matter. | text | null |
L_0982 | physical properties of matter | T_4712 | In addition to these properties, other physical properties of matter include the state of matter. States of matter include liquid, solid, and gaseous states. For example at 20 C, coal exists as a solid and water exists as a liquid. Additional examples of physical properties include: odor boiling point ability to conduct heat ability to conduct electricity ability to dissolve in other substances Some of these properties are illustrated in the Figures 1.1, 1.2, 1.3, and 1.4. Click image to the left or use the URL below. URL: The strong smell of swimming pool water is the odor of chlorine, which is added to the water to kill germs and algae. In con- trast, bottled spring water, which contains no chlorine, does not have an odor. Coolant is added to the water in a car radiator to keep the water from boiling and evaporating. Coolant has a higher boiling point than water and adding it to the water increases the boiling point of the solution. Q: The coolant that is added to a car radiator also has a lower freezing point than water. Why is this physical property useful? A: When coolant is added to water in a car radiator, it lowers the freezing point of the water. This prevents the water in the radiator from freezing when the temperature drops below 0 C, which is the freezing point of pure water. Q: Besides being able to conduct electricity, what other physical property of copper makes it well suited for electric wires? A: Copper, like other metals, is ductile. This means that it can be rolled and stretched into long thin shapes such as wires. This teakettle is made of aluminum except for its handle, which is made of plastic. Aluminum is a good conductor of heat. It conducts heat from the flames on the range to the water inside the kettle, so the water heats quickly. Plastic, on the other hand, is not a good conductor of heat. It stays cool enough to touch even when the rest of the teakettle becomes very hot. | text | null |
L_0982 | physical properties of matter | T_4712 | In addition to these properties, other physical properties of matter include the state of matter. States of matter include liquid, solid, and gaseous states. For example at 20 C, coal exists as a solid and water exists as a liquid. Additional examples of physical properties include: odor boiling point ability to conduct heat ability to conduct electricity ability to dissolve in other substances Some of these properties are illustrated in the Figures 1.1, 1.2, 1.3, and 1.4. Click image to the left or use the URL below. URL: The strong smell of swimming pool water is the odor of chlorine, which is added to the water to kill germs and algae. In con- trast, bottled spring water, which contains no chlorine, does not have an odor. Coolant is added to the water in a car radiator to keep the water from boiling and evaporating. Coolant has a higher boiling point than water and adding it to the water increases the boiling point of the solution. Q: The coolant that is added to a car radiator also has a lower freezing point than water. Why is this physical property useful? A: When coolant is added to water in a car radiator, it lowers the freezing point of the water. This prevents the water in the radiator from freezing when the temperature drops below 0 C, which is the freezing point of pure water. Q: Besides being able to conduct electricity, what other physical property of copper makes it well suited for electric wires? A: Copper, like other metals, is ductile. This means that it can be rolled and stretched into long thin shapes such as wires. This teakettle is made of aluminum except for its handle, which is made of plastic. Aluminum is a good conductor of heat. It conducts heat from the flames on the range to the water inside the kettle, so the water heats quickly. Plastic, on the other hand, is not a good conductor of heat. It stays cool enough to touch even when the rest of the teakettle becomes very hot. | text | null |
L_0982 | physical properties of matter | T_4712 | In addition to these properties, other physical properties of matter include the state of matter. States of matter include liquid, solid, and gaseous states. For example at 20 C, coal exists as a solid and water exists as a liquid. Additional examples of physical properties include: odor boiling point ability to conduct heat ability to conduct electricity ability to dissolve in other substances Some of these properties are illustrated in the Figures 1.1, 1.2, 1.3, and 1.4. Click image to the left or use the URL below. URL: The strong smell of swimming pool water is the odor of chlorine, which is added to the water to kill germs and algae. In con- trast, bottled spring water, which contains no chlorine, does not have an odor. Coolant is added to the water in a car radiator to keep the water from boiling and evaporating. Coolant has a higher boiling point than water and adding it to the water increases the boiling point of the solution. Q: The coolant that is added to a car radiator also has a lower freezing point than water. Why is this physical property useful? A: When coolant is added to water in a car radiator, it lowers the freezing point of the water. This prevents the water in the radiator from freezing when the temperature drops below 0 C, which is the freezing point of pure water. Q: Besides being able to conduct electricity, what other physical property of copper makes it well suited for electric wires? A: Copper, like other metals, is ductile. This means that it can be rolled and stretched into long thin shapes such as wires. This teakettle is made of aluminum except for its handle, which is made of plastic. Aluminum is a good conductor of heat. It conducts heat from the flames on the range to the water inside the kettle, so the water heats quickly. Plastic, on the other hand, is not a good conductor of heat. It stays cool enough to touch even when the rest of the teakettle becomes very hot. | text | null |
L_0984 | plasma | T_4715 | Compare and contrast the basic properties of matter, such as mass and volume. | text | null |
L_0984 | plasma | T_4716 | Here is a riddle for you to ponder: What do you and a tiny speck of dust in outer space have in common? Think you know the answer? Both you and the speck of dust consist of matter. So does the ground beneath your feet. In fact, everything you can see and touch is made of matter. The only things that are not matter are forms of energy. This would include things such as light and sound. Although forms of energy are not matter, the air and other substances they travel through are. So what is matter? Matter is defined as anything that has mass and volume. You may recall that atoms are the building blocks of matter. Even things as small as atoms have mass and volume. The more atoms, or matter, the more mass and volume are present. Different types of atoms have different amounts of mass and volume. So, its not enough to know the count of atoms to determine the mass. You must also know the type of atoms an item is made of. Mass and volume are just two ways to describe the physical property of a substance. Physical properties are all determined by the amounts and type of atoms that compose items. | text | null |
L_0984 | plasma | T_4717 | Mass refers to the amount of matter. Mass is usually measured with a balance. A balance allows an object to be matched with other objects of known mass. The SI unit for mass is the kilogram. For smaller masses, grams are often used instead. You may have a balance in your classroom. The balance may be either a triple-beam balance or an electronic balance. The figure below of the old-fashioned balance may give you a better idea of what mass is. What does it mean when both sides of the balance are at the same level? Thats correct, it would mean the masses of each object are equal. In that case, the fruit would have a mass of 1 kg. It would have the same mass as the iron. As you can see, the fruit is at a higher level than the iron. This means the fruit has less mass than the 1 kg iron object. Q: What If the fruit were at a lower level than the iron object? A: The mass of the fruit would be greater than 1 kg. | text | null |
L_0984 | plasma | T_4718 | Mass is often confused with weight. The two are closely related, but they are not the same. Mass is the amount of matter. Weight is a measure of the force of gravity acting on the mass. On Earth, the force of gravity is constant. If we are comparing objects on Earth, objects with a greater mass also have a greater weight. Weight is measured with a device called a scale. Remember, mass is measured with a balance. You might find an example of a scale in your kitchen or bathroom. Scales detect how forcefully objects are being pulled downward by gravity. The SI unit for weight is the newton (N). A mass of 10 kg has a weight of 100 newtons (N). | text | null |
L_0984 | plasma | T_4719 | At Earths gravity, what is the weight in newtons of an object with a mass of 10 kg? At Earths gravity, 1 kg has a weight of 10 N. Therefore, 10 kg has a weight of (10 kg x 10 m/s2 ) = 100 N. | text | null |
L_0984 | plasma | T_4720 | If you have a mass of 50 kg on Earth, what is your weight in newtons? An object with more mass is pulled by gravity with greater force. Mass and weight are closely related. However, the weight of an object can change if the force of gravity changes. On Earth, the force of gravity is the same everywhere. So how does the force of gravity change? It doesnt if you stay on Earth. What if we travel to another planet or moon in our solar system? Look at the photo of astronaut Edwin E. Aldrin Jr. taken by fellow astronaut Neil Armstrong in the Figure ??. They were the first humans to walk on the moon. An astronaut weighs less on the moon than he would on Earth. This is because the moons gravity is weaker than Earths. The astronauts mass, on the other hand, did not change. He still contained the same amount of matter on the moon as he did on Earth. If the astronaut weighed 175 pounds on Earth, he would have weighed only 29 pounds on the moon. If his mass on Earth was 80 kg, what would his mass have been on the moon? [Figure 3] | text | null |
L_0984 | plasma | T_4721 | The amount of space matter takes up is its volume. How the volume of matter is measured depends on its state. The volume of liquids is measured with measuring containers. In the kitchen, liquid volume is usually measured with measuring cups or spoons. In the lab, liquid volume is measured with containers such as graduated cylinders. Units in the metric system for liquid volume include liters (L) and milliliters (mL). The volume of gases depends on the volume of their container. Thats because gases expand to fill whatever space is available to them. For example, as you drink water from a bottle, air rushes in to take the place of the water. An "empty" liter bottle actually holds a liter of air. How could you find the volume of air in an "empty" room? The volume of regularly shaped solids can be calculated from their dimensions. For example, the volume of a rectangular solid is the product of its length, width, and height (l x w x h). For solids that have irregular shapes, the displacement method is used. You can see how it works in the video below. The SI unit for solid volumes is cubic meters (m3 ). However, cubic centimeters (cm3 ) are often used for smaller volume measurements. The displacement method is used to find the volume of irregularly shaped objects. It measures the amount of water that the object displaces, or moves out of the way. What is the volume of the toy dinosaur in mL? [See Figure ??] Click image to the left or use the URL below. URL: Q: How could you find the volume of air in an otherwise empty room? A: If the room has a regular shape, you could calculate its volume from its dimensions. For example, the volume of a rectangular room can be calculated with this formula: Volume = length width height If the length of the room is 5.0 meters, the width is 3.0 meters, and the height is 2.5 meters, then the volume of the room is: Volume = 5.0 m 3.0 m 2.5 m = 37.5 m3 Q: What is the volume of the dinosaur in the diagram above? A: The volume of the water alone is 4.8 mL. The volume of the water and dinosaur together is 5.6 mL. Therefore, the volume of the dinosaur alone is 5.6 mL - 4.8 mL = 0.8 mL. | text | null |
L_0984 | plasma | T_4722 | Density is also an important physical property of matter. The concept of density combines what we know about an objects mass and volume. Density reflects how closely packed the particles of matter are. When particles are packed together more tightly, matter is more dense. Differences in density of matter explain many phenomena. It explains why helium balloons rise. It explains why currents such as the Gulf Stream flow through the oceans. It explains why some things float in or sink. You can see this in action by pouring vegetable oil into water. You can see a colorful demonstration in this video. Click image to the left or use the URL below. URL: To better understand density, think about a bowling ball and volleyball, pictured in the Figure 1.1. Imagine lifting each ball. The two balls have about the same volume. The bowling ball feels much heavier than the volleyball, but why? It is because the bowling ball is made of solid plastic. Plastic contains a lot of tightly packed particles of matter. In contrast, the volleyball is full of a gas (air). The air atoms are further apart than in the solid bowling ball. Therefore, the matter inside the bowling ball is more dense than the matter inside the volleyball. Q: If you ever went bowling, you may have noticed that all the bowling balls are the same size. This means they have the same volume. Even though they are the same size, some bowling balls feel heavier than others. How can this be? A: Bowling balls that feel lighter are made of matter that is less dense. | text | null |
L_0984 | plasma | T_4723 | The density of matter is actually the amount of matter in a given space. The amount of matter is measured by its mass. The space matter takes up is measured by its volume. Therefore, the density of matter can be calculated with this formula: Density = mass volume Assume, for example, that a book has a mass of 500 g and a volume of 1000 cm3 . Then the density of the book is: Density = 500 g = 0.5 g/cm3 1000 cm3 Q: What is the density of a liquid that has a volume of 30 mL and a mass of 300 g? A: The density of the liquid is: Density = 300 g = 10 g/mL 30 mL | text | null |
L_0984 | plasma | T_4724 | By clicking a link below, you will leave the CK-12 site and open an external site in a new tab. This page will remain open in the original tab. | text | null |
L_0993 | properties of solutions | T_4756 | Salt water in the ocean is a solution. In a solution, one substance, called the solute, dissolves in another substance, called the solvent. In ocean water, salt is the solute and water is the solvent. When a solute dissolves in a solvent, it changes the physical properties of the solvent. In particular, the solute generally lowers the freezing point of the solvent, which is called freezing point depression, and raises the boiling point of the solvent, which is called boiling point elevation. For example, adding either salt to water lowers the freezing point and raises the boiling point of the water. | text | null |
L_0993 | properties of solutions | T_4757 | Pure water freezes at 0 C, but the salt water in the ocean freezes at -2.2 C because of freezing point depression. We take advantage of the freezing point depression of salt in water by putting salt on ice to melt it. Thats why the truck in the Figure 1.1 is spreading salt on an icy road. Did you ever see anyone add a fluid to their car radiator? The fluid might be antifreeze, like in the Figure 1.2. Antifreeze lowers the temperature of the water in the car radiator so it wont freeze, even when the temperature falls far below 0 C. For example, a 50 percent antifreeze solution wont freeze unless the temperature goes below -37 C. | text | null |
L_0993 | properties of solutions | T_4757 | Pure water freezes at 0 C, but the salt water in the ocean freezes at -2.2 C because of freezing point depression. We take advantage of the freezing point depression of salt in water by putting salt on ice to melt it. Thats why the truck in the Figure 1.1 is spreading salt on an icy road. Did you ever see anyone add a fluid to their car radiator? The fluid might be antifreeze, like in the Figure 1.2. Antifreeze lowers the temperature of the water in the car radiator so it wont freeze, even when the temperature falls far below 0 C. For example, a 50 percent antifreeze solution wont freeze unless the temperature goes below -37 C. | text | null |
L_0993 | properties of solutions | T_4758 | Antifreeze could also be called antiboil because it also raises the boiling point of the water in a car radiator. Hot weather combined with a hot engine can easily raise the temperature of the water in the radiator above 100 C, which is the boiling point of pure water. If the water boils, it could cause the engine to overheat and become seriously damaged. However, if antifreeze has been added to the water, the boiling point is much higher. For example a 50 percent antifreeze solution has a boiling point of 129 C. Unless the water gets hotter than this, it wont boil and ruin the engine. | text | null |
L_1001 | rate of dissolving | T_4782 | Did you ever get impatient and start drinking a sweetened drink before all the sugar has dissolved? As you drink the last few drops, you notice that some of the sugar is sitting on the bottom of the container. Q: What could you do to dissolve the sugar faster? A: The rate of dissolving is influenced by several factors, including stirring, temperature of solvent, and size of solute particles. | text | null |
L_1001 | rate of dissolving | T_4783 | Stirring a solute into a solvent speeds up the rate of dissolving because it helps distribute the solute particles throughout the solvent. For example, when you add sugar to iced tea and then stir the tea, the sugar will dissolve faster. If you dont stir the iced tea, the sugar may eventually dissolve, but it will take much longer. | text | null |
L_1001 | rate of dissolving | T_4784 | The temperature of the solvent is another factor that affects how fast a solute dissolves. Generally, a solute dissolves faster in a warmer solvent than it does in a cooler solvent because particles have more energy of movement. For example, if you add the same amount of sugar to a cup of hot tea and a cup of iced tea, the sugar will dissolve faster in the hot tea. | text | null |
L_1001 | rate of dissolving | T_4785 | A third factor that affects the rate of dissolving is the size of solute particles. For a given amount of solute, smaller particles have greater surface area. With greater surface area, there can be more contact between particles of solute and solvent. For example, if you put granulated sugar in a glass of iced tea, it will dissolve more quickly than the same amount of sugar in a cube (see Figure 1.1). Thats because all those tiny particles of granulated sugar have greater total surface area than a single sugar cube. | text | null |
L_1004 | refraction | T_4791 | Physical properties of matter can be measured and observed. Physical properties can be detected with your senses . For example, they may be things that you can see, hear, smell, feel, or even taste. Q: What are some differences between snow and sand? Which senses could you use to find out the differences? A: You can see that snow and sand have a different color . You can also feel that snow is softer than sand. Both color and hardness are physical properties of matter . You can notice that ice will melt at room temperature. Sand will remain a solid at room temperature. | text | null |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.