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L_0714 | introduction to solutions | T_3512 | When a solute dissolves in a solvent, it changes the physical properties of the solvent. Two properties that change when a solute is added are the freezing and boiling points. Generally, solutes lower the freezing point and raise the boiling point of solvents. You can see some examples of this in Figure below. To see why solutes change the freezing and boiling points of solvents, watch this video: (14:00). MEDIA Click image to the left or use the URL below. URL: In each of these examples, a solute changes the freezing and/or boiling points of a solvent. | text | null |
L_0715 | solubility and concentration | T_3513 | Solubility is the amount of solute that can dissolve in a given amount of solvent at a given temperature. Some solutes have greater solubility than others in a given solvent. For example, table sugar is much more soluble in water than is baking soda. You can dissolve much more sugar than baking soda in a given amount of water. Compare the solubility of these and other solutes in Figure 10.2. For a video about solubility, go to this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0715 | solubility and concentration | T_3514 | There is a limit on the amount of solute that can dissolve in a given solvent. Tanya found this out with her baking soda mixture. But even sugar, which is very soluble, has an upper limit. The maximum amount of table sugar that will dissolve in 1 L of water at 20C is about 2000 g. If you add more sugar than this, the extra sugar wont dissolve. A solution that contains as much solute as can dissolve at a given temperature is called a saturated solution. A solution that contains less solute than can dissolve at a given temperature is called an unsaturated solution. A solution of 2000 grams of sugar in 1 L of 20C water is saturated. Thats all the sugar the solution can hold. Any solution containing less than 2000 g of sugar is unsaturated. It can hold more sugar. To learn more about saturated and unsaturated solutions, watch the video at this URL: . You Try It! Problem: A solution contains 249 grams of Epsom salt in 1 L of water at 20C. Is the solution saturated or unsaturated? Problem: Give an example of an unsaturated solution of table salt in 1 L of 20C water. | text | null |
L_0715 | solubility and concentration | T_3515 | Certain factors can change the solubility of a solute. Temperature is one such factor. How temperature affects solubility depends on the state of the solute, as you can see in Figure 10.3. If a solute is a solid or liquid, increasing the temperature increases its solubility. For example, more sugar can dissolve in hot tea than in iced tea. If a solute is a gas, increasing the temperature decreases its solubility. For example, less carbon dioxide can dissolve in warm ocean water than in cold ocean water. The solubility of gases is also affected by pressure. Pressure is the amount of force pushing against a given area. Increasing the pressure on a gas increases its solubility. Did you ever open a can of soda and notice how it fizzes out of the can? Soda contains carbon dioxide. Opening the can reduces the pressure on the gas so it is less soluble. As a result, some of the carbon dioxide comes out of solution and rushes into the air. Do you wonder why temperature and pressure affect solubility in these ways? If so, watch the video at the URL below. It explains why. | text | null |
L_0715 | solubility and concentration | T_3515 | Certain factors can change the solubility of a solute. Temperature is one such factor. How temperature affects solubility depends on the state of the solute, as you can see in Figure 10.3. If a solute is a solid or liquid, increasing the temperature increases its solubility. For example, more sugar can dissolve in hot tea than in iced tea. If a solute is a gas, increasing the temperature decreases its solubility. For example, less carbon dioxide can dissolve in warm ocean water than in cold ocean water. The solubility of gases is also affected by pressure. Pressure is the amount of force pushing against a given area. Increasing the pressure on a gas increases its solubility. Did you ever open a can of soda and notice how it fizzes out of the can? Soda contains carbon dioxide. Opening the can reduces the pressure on the gas so it is less soluble. As a result, some of the carbon dioxide comes out of solution and rushes into the air. Do you wonder why temperature and pressure affect solubility in these ways? If so, watch the video at the URL below. It explains why. | text | null |
L_0715 | solubility and concentration | T_3516 | The concentration of a solution is the amount of solute in a given amount of solution. A solution with little dissolved solute has a low concentration. It is called a dilute solution. A solution with a lot of dissolved solute has a high concentration. It is called a concentrated solution. Concentration is often expressed as a percent. You can calculate the concentration of a solution using this formula: Concentration = Mass (or Volume) of Solute 100% Mass (or Volume) of Solution For example, if a 100 g solution of salt water contains 3 g of salt, then its concentration is: Concentration = 3g 100% = 3% 100 g For some problems that are more challenging, go to these URLs: MEDIA Click image to the left or use the URL below. URL: MEDIA Click image to the left or use the URL below. URL: You Try It! Problem: A 1 L container of juice drink, called brand A, contains 250 mL of juice. The rest of the drink is water. How concentrated is brand A juice drink? Problem: A 600 mL container of another juice drink, called brand B, contains 200 mL of juice. Which brand of juice drink is more concentrated, brand A or brand B? | text | null |
L_0757 | electric charge | T_3848 | Electric charge is a physical property of particles or objects that causes them to attract or repel each other without touching. All electric charge is based on the protons and electrons in atoms. A proton has a positive electric charge, and an electron has a negative electric charge (see Figure 23.2). When it comes to electric charges, opposites attract. In other words, positive and negative particles are attracted to each other. Like charges, on the other hand, repel each other, so two positive or two negative charges push apart from each other. The force of attraction or repulsion between charged particles is called electric force. It is illustrated in Figure 23.3. The strength of electric force depends on the amount of electric charge and the distance between the charged particles. The larger the charge or the closer together the charges are, the greater is the electric force. | text | null |
L_0757 | electric charge | T_3848 | Electric charge is a physical property of particles or objects that causes them to attract or repel each other without touching. All electric charge is based on the protons and electrons in atoms. A proton has a positive electric charge, and an electron has a negative electric charge (see Figure 23.2). When it comes to electric charges, opposites attract. In other words, positive and negative particles are attracted to each other. Like charges, on the other hand, repel each other, so two positive or two negative charges push apart from each other. The force of attraction or repulsion between charged particles is called electric force. It is illustrated in Figure 23.3. The strength of electric force depends on the amount of electric charge and the distance between the charged particles. The larger the charge or the closer together the charges are, the greater is the electric force. | text | null |
L_0757 | electric charge | T_3849 | Electric force is exerted over a distance, so charged particles do not have to be in contact in order to exert force over each other. Thats because each charged particle is surrounded by an electric field. An electric field is a space around a charged particle where the particle exerts electric force on other particles. Electric fields surrounding positively and negatively charged particles are illustrated in Figure 23.4 and at the URL below. When charged particles exert force on each other, their electric fields interact. This is also illustrated in Figure 23.4. | text | null |
L_0757 | electric charge | T_3850 | Atoms are neutral in electric charge because they have the same number of electrons as protons. However, atoms may transfer electrons and become charged ions, as illustrated in Figure 23.5. Positively charged ions, or cations, form when atoms give up electrons. Negatively charged ions, or anions, form when atoms gain electrons. Like the formation of ions, the formation of charged matter in general depends on the transfer of electrons either between two materials or within a material. Three ways this can occur are friction, conduction, and polarization. In all cases, the total charge remains the same. Electrons move, but they arent destroyed. This is the law of conservation of charge. | text | null |
L_0757 | electric charge | T_3851 | Did you ever rub an inflated balloon against your hair? You can see what happens in Figure 23.6. Friction between the rubber of the balloon and the babys hair results in electrons from the hair "rubbing off" onto the balloon. Thats because rubber attracts electrons more strongly than hair does. After the transfer of electrons, the balloon becomes negatively charged and the hair becomes positively charged. As a result, the individual hairs repel each other and the balloon and the hair attract each other. Electrons are transferred in this way whenever there is friction between materials that differ in their ability to give up or accept electrons. | text | null |
L_0757 | electric charge | T_3852 | Another way electrons may be transferred is through conduction. This occurs when there is direct contact between materials that differ in their ability to give up or accept electrons. For example, wool tends to give up electrons and rubber tends to accept them. Therefore, when you walk across a wool carpet in rubber-soled shoes, electrons transfer from the carpet to your shoes. You become negatively charged, while the carpet becomes positively charged. Another example of conduction is pictured in Figure 23.7. The device this girl is touching is called a van de Graaff generator. The dome on top is negatively charged. When the girl places her hand on the dome, electrons are transferred to her, so she becomes negatively charged as well. Even the hairs on her head become negatively charged. As a result, individual hairs repel each other, causing them to stand on end. You can see a video demonstration of a van de Graff generator at this URL: . | text | null |
L_0757 | electric charge | T_3853 | Polarization is the movement of electrons within a neutral object due to the electric field of a nearby charged object. It occurs without direct contact between the two objects. You can see how it happens in Figure 23.8. When the negatively charged plastic rod in the figure is placed close to the neutral metal plate, electrons in the plate are repelled by the positive charges in the rod. The electrons move away from the rod, causing one side of the plate to become positively charged and the other side to become negatively charged. Polarization may also occur after you walk across a wool carpet in rubber-soled shoes and become negatively charged. If you reach out to touch a metal doorknob, electrons in the neutral metal will be repelled and move away from your hand before you even touch the knob. In this way, one end of the doorknob becomes positively charged and the other end becomes negatively charged. | text | null |
L_0757 | electric charge | T_3854 | Polarization leads to the buildup of electric charges on objects. This buildup of charges is known as static electricity. Once an object becomes charged, it is likely to remain charged until another object touches it or at least comes very close to it. Thats because electric charge cannot travel easily through air, especially if the air is dry. Consider again the example of your hand and the metal doorknob. When your negatively charged hand gets very close to the positively charged doorknob, the air between your hand and the knob may become electrically charged. If that happens, it allows electrons to suddenly flow from your hand to the knob. This is the electric shock you feel when you reach for the knob. You may even see a spark as the electrons jump from your hand to the metal. This sudden flow of electrons is called static discharge. Another example of static discharge, on a much larger scale, is lightning. You can see how it occurs in Figure 23.9. At the URL below, you can watch a slow-motion lightning strike. Be sure to wait for the real-time lightning strike at the very end of the video. | text | null |
L_0758 | electric current | T_3855 | Electric current is a continuous flow of electric charges. 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, or it may keep reversing direction. When current flows in just one direction, it is called direct current (DC). The current that flows through a battery-powered flashlight is direct current. When current keeps reversing direction, it is called alternating current (AC). The current that runs through the wires in your home is alternating current. Graphs of both types of current are shown in Figure 23.10. You can watch an animation of both types at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0758 | electric current | T_3856 | Why do charges flow in an electric current? The answer has to do with electric potential energy. Potential energy is stored energy that an object has due to its position or shape. An electric charge has potential energy because of its position 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 move apart, their potential energy decreases. Electric charges always move spontaneously from a position where they have higher potential energy to a position where their potential energy is lower. This is similar to water falling over a dam from an area of higher to lower potential energy due to gravity. In general, for an electric charge to move from one position to another, there must be a difference in electric potential energy between the two positions. The difference in electric potential energy is called potential difference, or voltage. Voltage is measured in an SI unit called the volt (V). For example, the terminals of the car battery in Figure 23.11 have a potential difference of 12 volts. This difference in voltage results in a spontaneous flow of charges, or electric current. | text | null |
L_0758 | electric current | T_3857 | Batteries like the one in Figure 23.11 are one of several possible sources of voltage needed to produce electric current. Sources of voltage include generators, chemical cells, and solar cells. Generators change the kinetic energy of a spinning turbine to electrical energy in a process called electromag- netic induction. You can read about generators and how they work in the chapter "Electromagnetism." Chemical and solar cells are devices that change chemical or light energy to electrical energy. You can read about both types of cells and how they work below. | text | null |
L_0758 | electric current | T_3858 | Chemical cells are found in batteries. They produce voltage by means of chemical reactions. A chemical cell has two electrodes, which are strips made of different materials, such as zinc and carbon (see Figure 23.12). The electrodes are suspended in an electrolyte. An electrolyte is a substance containing free ions that can carry electric current. The electrolyte may be either a paste, in which case the cell is called a dry cell, or a liquid, in which case the cell is called a wet cell. Flashlight batteries contain dry cells. Car batteries contain wet cells. Animations at the URL below show how batteries work. Both dry and wet cells work the same basic way. The electrodes react chemically with the electrolyte, causing one electrode to give up electrons and the other electrode to accept electrons. In the case of zinc and carbon electrodes, the zinc electrode attracts electrons and becomes negatively charged, while the carbon electrode gives up electrons and becomes positively charged. Electrons flow through the electrolyte from the negative to positive electrode. If wires are used to connect the two electrodes at their terminal ends, electric current will flow through the wires and can be used to power a light bulb or other electric device. | text | null |
L_0758 | electric current | T_3859 | Solar cells convert the energy in sunlight to electrical energy. They contain a material such as silicon that absorbs light energy and gives off electrons. The electrons flow and create electric current. Figure 23.13 and the animation at the URL below show how a solar cell uses light energy to produce electric current and power a light bulb. Many calculators and other devices are also powered by solar cells. | text | null |
L_0758 | electric current | T_3859 | Solar cells convert the energy in sunlight to electrical energy. They contain a material such as silicon that absorbs light energy and gives off electrons. The electrons flow and create electric current. Figure 23.13 and the animation at the URL below show how a solar cell uses light energy to produce electric current and power a light bulb. Many calculators and other devices are also powered by solar cells. | text | null |
L_0758 | electric current | T_3860 | Electric current cannot travel through empty space. It needs a material through which to travel. However, when current travels through a material, the flowing electrons collide with particles of the material, and this creates resistance. | text | null |
L_0758 | electric current | T_3861 | Resistance is opposition to the flow of electric charges that occurs when electric current travels through matter. The SI unit of resistance is the ohm (named for the scientist Georg Ohm, whom you can read about below). Resistance is caused by electrons in a current bumping into electrons and ions in the matter through which the current is flowing. Resistance is similar to the friction that resists the movement of one surface as it slides over another. Resistance reduces the amount of current that can travel through the material because some of the electrical energy is converted to other forms of energy. For example, when electric current flows through the tungsten wire inside an incandescent light bulb, the tungsten resists the flow of electric charge, and some of the electrical energy is converted to light and thermal energy. | text | null |
L_0758 | electric current | T_3862 | Some materials resist the flow of electric current more or less than other materials do. Materials that have low resistance to electric current are called electric conductors. Many metalsincluding copper, aluminum, and steelare good conductors of electricity. Water that has even a tiny amount of impurities in it is an electric conductor as well. Materials that have high resistance to electric current are called electric insulators. Wood, rubber, and plastic are examples of electric insulators. Dry air is also an electric insulator. You probably know that electric wires are made of metal and coated with rubber or plastic (see Figure 23.14). Now you know why. Metals are good electric conductors, so they offer little resistance and allow most of the current to pass through. Rubber and plastic are good insulators, so they offer a lot of resistance and allow little current to pass through. 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 a metal wire and none flows through its rubber or plastic coating. | text | null |
L_0758 | electric current | T_3863 | For a given material, three properties of the material determine how resistant it is to electric current: length, width, and temperature. Consider an electric wire like one of the wires in Figure 23.14. A longer wire has more resistance. Current must travel farther, so there are more chances for it to collide with particles of wire. A wider wire has less resistance. A given amount of current has more room to flow through a wider wire. A cooler wire has less resistance than a warmer wire. Cooler particles have less kinetic energy, so they move more slowly. Current is less likely to collide with slowly moving particles. Materials called superconductors have virtually no resistance when they are cooled to extremely low temperatures. | text | null |
L_0758 | electric current | T_3864 | Voltage, or a difference in electric potential energy, is needed for electric current to flow. As you might have guessed, greater voltage results in more current. Resistance, on the other hand, opposes the flow of electric current, so greater resistance results in less current. These relationships between current, voltage, and resistance were first demonstrated by a German scientist named Georg Ohm in the early 1800s, 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_0758 | electric current | T_3865 | You may have a better understanding of Ohms law if you compare current flowing through a wire from a battery to water flowing through a garden hose from a tap. Increasing voltage is like opening the tap wider. When the tap is opened wider, more water flows through the hose. This is like an increase in current. Stepping on the hose makes it harder for the water to pass through. This is like increasing resistance, which causes less current to flow through a material. Still not sure about the relationship among voltage, current, and resistance? Watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0758 | electric current | T_3866 | You can use the equation for current (above) to calculate the amount of current flowing through a material when voltage and resistance are known. Consider an electric wire that is connected to a 12-volt battery. If the wire has a resistance of 3 ohms, how much current is flowing through the wire? Current = 12 volts = 4 amps 3 ohms You Try It! Problem: A 120-volt voltage source is connected to a wire with 20 ohms of resistance. How much current flows through the wire? | text | null |
L_0759 | electric circuits | T_3867 | A closed loop through which current can flow is called an electric circuit. In homes in the U.S., most electric circuits have a voltage of 120 volts. The amount of current (amps) a circuit carries depends on the number and power of electrical devices connected to the circuit. But home circuits generally have a safe upper limit of about 20 or 30 amps. | text | null |
L_0759 | electric circuits | T_3868 | All electric circuits have at least two parts: a voltage source and a conductor. The voltage source of the circuit in Figure 23.16 is a battery. In a home circuit, the source of voltage is an electric power plant, which may supply electric current to many homes and businesses in a community or even to many communities. The conductor in most circuits consists of one or more wires. The conductor must form a closed loop from the source of voltage and back again. In Figure 23.16, the wires are connected to both terminals of the battery, so they form a closed loop. The circuit in Figure 23.16 also has two other parts: a light bulb and a switch. Most circuits have devices such as light bulbs that convert electric energy to other forms of energy. In the case of a light bulb, electricity is converted to light and thermal energy. Many circuits have switches to control the flow of current through the circuit. When the switch is turned on, the circuit is closed and current can flow through it. When the switch is turned off, the circuit is open and current cannot flow through it. | text | null |
L_0759 | electric circuits | T_3869 | 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 that show how the wiring and other electrical components are to be installed in order to supply current to appliances, lights, and other electrical devices in the home. You can see an example of a very simple circuit diagram in Figure 23.17. Different parts of the circuit are represented by standard symbols, as defined in the figure. 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. It could be a light bulb, doorbell, or similar device. | text | null |
L_0759 | electric circuits | T_3870 | There are two basic types of electric circuits, called series and parallel circuits. They differ in the number of loops through which current can flow. You can see an example of each type of circuit in Figure 23.18. A series circuit has only one loop through which current can flow. If the circuit is interrupted at any point in the loop, no current can flow through the circuit and no devices in the circuit will work. In the series circuit in Figure 23.18, if one light bulb burns out the other light bulb will not work because it wont receive any current. Series circuits are commonly used in flashlights. You can see an animation of a series circuit at this URL: http://regentsprep.org/regents/physics/phys03/bsercir/default.htm . A parallel circuit has two (or more) loops through which current can flow. If the circuit is interrupted in one of the loops, current can still flow through the other loop(s). For example, if one light bulb burns out in the parallel circuit in Figure 23.18, the other light bulb will still work because current can by-pass the burned-out bulb. The wiring in a house consists of parallel circuits. You can see an animation of a parallel circuit at this URL: http://regentsprep.org/regents/physics/phys03/bsercir/default.htm . | text | null |
L_0759 | electric circuits | T_3871 | We use electricity for many purposes. Devices such as lights, stoves, and stereos all use electricity and convert it to energy in other forms. However, devices may vary in how quickly they change electricity to other forms of energy. | text | null |
L_0759 | electric circuits | T_3872 | The rate at which a device changes electric current to another form of energy is called electric power. The SI unit of 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 microwave, can be calculated if you know the current and voltage of the circuit. This equation shows how power, current, and voltage are related: Power (watts) = Current (amps) Voltage (volts) Consider a microwave that is plugged into a home circuit. Assume the microwave is the only device connected to the circuit. If the voltage of the circuit is 120 volts and it carries 10 amps of current, then the power of the microwave is: Power = 120 volts 10 amps = 1200 watts, or 1.2 kilowatts You Try It! Problem: A hair dryer is connected to a 120-volt circuit that carries 12 amps of current. What is the power of the hair dryer in kilowatts? | text | null |
L_0759 | electric circuits | T_3873 | Did you ever wonder how much electrical energy it takes to use an appliance such as a microwave or hair dryer? Electrical energy use depends on the power of the appliance and how long it is used. It can be represented by the equation: Electrical Energy = Power Time 1 Suppose you use a 1.2-kilowatt microwave for 5 minutes ( 12 hour). Then the energy used would be: Electrical Energy = 1.2 kilowatts 1 hour = 0.1 kilowatt-hours 12 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. Therefore, the 0.1 kilowatt-hours used by the microwave equals 0.36 million joules of energy. You Try It! Problem: A family watches television for an average of 2 hours per day. The television has 0.12 kilowatts of power. How much electrical energy does the family use watching television each day? | text | null |
L_0759 | electric circuits | T_3874 | Electricity is dangerous. Contact with electric current can cause severe burns and even death. Electricity can also cause serious fires. A common cause of electric hazards and fires is a short circuit. | text | null |
L_0759 | electric circuits | T_3875 | An electric cord contains two wires. One wire carries current from the outlet to the appliance or other electric device, and one wire carries current back to the outlet. Did you ever see an old appliance with a damaged cord, like the one in Figure 23.19? 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. For example, 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_0759 | electric circuits | T_3876 | Because electricity can be so dangerous, safety features are built into electric circuits and devices. They include three-prong plugs, circuit breakers, and GFCI outlets. Each feature is described and illustrated in Table 23.1. You can learn more about electric safety features in the home by watching the video at this URL: Electric Safety Feature Three-Prong Plug Circuit Breaker Description A three-prong plug is generally used on metal appli- ances. The two flat prongs carry current to and from the appliance. The round prong is for safety. It connects with a wire inside the outlet that goes down into the ground. If any stray current leaks from the circuit or if there is a short circuit, the ground wire carries the current into the ground, which harmlessly absorbs it. A circuit breaker is a switch that automatically opens a circuit if too much current flows through it. This could happen if too many electric devices are plugged into the circuit or if there is an electric short. Once the problem is resolved, the circuit breaker can be switched back on to close the circuit. Circuit breakers are generally found in a breaker box that controls all the circuits in a building. Electric Safety Feature GFCI Outlet Description 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 amounts 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 opens the circuit. The breaker can be reset by pushing a button on the outlet cover. | text | null |
L_0759 | electric circuits | T_3877 | Even with electric safety features, electricity is still dangerous if it is not used safely. Follow the safety rules below to reduce the risk of injury or fire from electricity. Never mix electricity and water. Dont turn on or plug in 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 very good electric conductor. 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. Plugging in other objects is likely to cause a serious shock that could be fatal. Never go near fallen electric lines. They could be carrying a lot of current. Report fallen lines to the electric company as soon as possible. | text | null |
L_0760 | electronics | T_3878 | Did you ever make a secret code? One way to make a code is to represent each letter of the alphabet by a different number. Then you can send a coded message by writing words as strings of digits. This is similar to how information is encoded using an electric current. The voltage of the current is changed rapidly and repeatedly to encode a message, called an electronic signal. There are two different types of electronic signals: analog signals and digital signals. Both are illustrated in Figure 23.20. A digital signal consists of pulses of voltage, created by repeatedly switching the current off and on. 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. DVDs, for example, encode sounds and pictures as digital signals. An analog signal consists of continuously changing voltage in a circuit. For example, microphones encode sounds as analog signals. | text | null |
L_0760 | electronics | T_3879 | Electronic components are the parts used in electronic devices such as computers. The components transmit and change electric current. They are made of materials called semiconductors. | text | null |
L_0760 | electronics | T_3880 | A semiconductor is a solid crystalusually consisting mainly of siliconthat can conduct current better than an electric insulator but not as well as an electric conductor. Very small amounts of other elements, such as boron or phosphorus, are added to the silicon so it can conduct current. A semiconductor is illustrated in Figure 23.21. There are two different types of semiconductors: n-type and p-type. An n-type semiconductor consists of silicon and an element such as phosphorus that gives the silicon crystal extra electrons. An n-type semiconductor is like the negative terminal in a chemical cell. A p-type semiconductor consists of silicon and an element such as boron that gives the silicon positively charged holes where electrons are missing. A p-type semiconductor is like the positive terminal in a chemical cell. | text | null |
L_0760 | electronics | T_3881 | Electronic components contain many semiconductors. Types of components include diodes, transistors, and inte- grated circuits. Each type is described in Table 23.2. Electronic Component Diode Transistor Integrated Circuit (Microchip) Description A diode consists of a p-type and an n-type semicon- ductor placed side by side. 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. A transistor consists of three semiconductors, either p- n-p or n-p-n. Current cant flow through a transistor unless a small amount of current is applied to the center semiconductor (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. You can learn more about transistors and how they work at this URL: http An integrated circuitalso called a microchipis a tiny, flat piece of silicon that consists of layers of elec- tronic components such as transistors. An integrated circuit as small as a fingernail can contain millions of electronic components. Current flows extremely rapidly in an integrated circuit because it doesnt have far to travel. You can learn how microprocessors are made at this URL: | text | null |
L_0760 | electronics | T_3882 | Many of the devices you commonly use are electronic. Electronic devices include computers, mobile phones, TV remotes, DVD and CD players, game systems, MP3 players, and digital cameras. All of these devices use electric current to encode, analyze, or transmit information. Consider the computer as an example of an electronic device. A computer contains microchips with millions of tiny electronic components. Information is encoded as 0s and 1s and transmitted as electrical pulses. One digit (either 0 or 1) is called a bit, which stands for "binary digit." Each group of eight digits is called a byte. A gigabyte is a billion bytes thats 8 billion 0s and 1s! 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 in Figure 23.22 and described below. 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. You can learn more about CPUs and how they work by watching the video at this URL: . 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. | text | null |
L_0763 | electricity and magnetism | T_3897 | In 1820, a physicist in Denmark, named Hans Christian Oersted, discovered how electric currents and magnetic fields are related. However, it was just a lucky accident. Oersted, who is pictured in Figure 25.1, was presenting a demonstration to his students. Ironically, he was trying to show that electricity and magnetism are not related. He placed a wire with electric current flowing through it next to a magnet, and nothing happened. After class, a student held the wire near the magnet again, but in a different direction. To Oersteds surprise, the pointer of the magnet swung toward the wire so it was no longer pointing to Earths magnetic north pole. Oersted was intrigued. He turned off the current in the wire to see what would happen to the magnet. The pointer swung back to its original position, pointing north again. Oersted had discovered that an electric current creates a magnetic field. The magnetic field created by the current was strong enough to attract the pointer of the nearby compass. Oersted wanted to learn more about the magnetic field created by a current, so he placed a magnet at different locations around a wire with current flowing through it. You can see some of his results in Figure 25.2. They show that the magnetic field created by a current has field lines that circle around the wire. You can learn more about Oersteds investigations of current and magnetism at the URL below. MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0763 | electricity and magnetism | T_3897 | In 1820, a physicist in Denmark, named Hans Christian Oersted, discovered how electric currents and magnetic fields are related. However, it was just a lucky accident. Oersted, who is pictured in Figure 25.1, was presenting a demonstration to his students. Ironically, he was trying to show that electricity and magnetism are not related. He placed a wire with electric current flowing through it next to a magnet, and nothing happened. After class, a student held the wire near the magnet again, but in a different direction. To Oersteds surprise, the pointer of the magnet swung toward the wire so it was no longer pointing to Earths magnetic north pole. Oersted was intrigued. He turned off the current in the wire to see what would happen to the magnet. The pointer swung back to its original position, pointing north again. Oersted had discovered that an electric current creates a magnetic field. The magnetic field created by the current was strong enough to attract the pointer of the nearby compass. Oersted wanted to learn more about the magnetic field created by a current, so he placed a magnet at different locations around a wire with current flowing through it. You can see some of his results in Figure 25.2. They show that the magnetic field created by a current has field lines that circle around the wire. You can learn more about Oersteds investigations of current and magnetism at the URL below. MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0763 | electricity and magnetism | T_3898 | The magnetic field created by a current flowing through a wire actually surrounds the wire in concentric circles. This magnetic field is stronger if more current is flowing through the wire. The direction of the magnetic field also depends on the direction that the current is flowing through the wire. 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 right hand rule is illustrated in Figure 25.3. 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. You can see the right hand rule in action at this URL: . | text | null |
L_0764 | using electromagnetism | T_3899 | A solenoid is a coil of wire with electric current flowing through it, giving it a magnetic field (see Figure 25.5). Recall that current flowing through a straight wire produces a weak electromagnetic field that circles around the wire. Current flowing through a coil of wire, in contrast, produces a magnetic field that has north and south poles like a bar magnet. The magnetic field around a coiled wire is also stronger than the magnetic field around a straight wire because each turn of the wire has its own magnetic field. Adding more turns increases the strength of the field, as does increasing the amount of current flowing through the coil. You can see an actual solenoid with a compass showing its magnetic north pole at this URL: . | text | null |
L_0764 | using electromagnetism | T_3900 | Solenoids are the basis of electromagnets. An electromagnet is a solenoid wrapped around a bar of iron or other ferromagnetic material (see Figure 25.6). The electromagnetic field of the solenoid magnetizes the iron bar by aligning its magnetic domains. The combined magnetic force of the magnetized iron bar and the wire coil makes an electromagnet very strong. In fact, electromagnets are the strongest magnets made. Some of them are strong enough to lift a train. The maglev train described earlier, in the lesson "Electricity and Magnetism," contains permanent magnets. Strong electromagnets in the track repel the train magnets, causing the train to levitate above the track. Like a solenoid, an electromagnet is stronger if there are more turns in the coil or more current is flowing through it. A bigger bar or one made of material that is easier to magnetize also increases an electromagnets strength. You can see how to make a simple electromagnet at this URL: (4:57). MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0764 | using electromagnetism | T_3901 | Many common electric devices contain electromagnets. Some examples include hair dryers, fans, CD players, telephones, and doorbells. Most electric devices that have moving parts contain electric motors. You can read below how doorbells and electric motors use electromagnets. | text | null |
L_0764 | using electromagnetism | T_3902 | Figure 25.7 shows a diagram of 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 voltage source, an electromagnet, and the clapper of a bell. When current flows through the 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. The clapper returns to its original position, which 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 as long as the button by the front door is being pressed. | text | null |
L_0764 | using electromagnetism | T_3903 | An electric motor is a device that uses an electromagnet to change electrical energy to kinetic energy. Figure 25.8 shows a simple diagram of an electric motor. The motor contains an electromagnet that is connected to a shaft. When current flows through the motor, the electromagnet turns, causing the shaft to turn as well. The rotating shaft moves other parts of the device. Why does the motors electromagnet turn? Notice that 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 turn 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 once again repelled by the like poles of the permanent magnets. This causes the electromagnet to continue to turn. These events keep repeating, so the electromagnet rotates continuously. You can make a very simple electric motor with a battery, wire, and magnet following instructions at this URL: . | text | null |
L_0765 | generating and using electricity | T_3904 | Just about a decade after Oersted discovered that electric current produces a magnetic field, an English scientist named Michael Faraday discovered that the reverse is also true. A magnetic field produces an electric current, as long as the magnetic field is changing. This is called Faradays law. | text | null |
L_0765 | generating and using electricity | T_3905 | The process of generating electric current with a changing magnetic field is called electromagnetic induction. 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 magnetic field lines. One way this can happen is pictured in Figure 25.9. It shows a magnet moving inside a wire coil. Another way is for the coil to move instead of the magnet. You can watch an animated version of Figure 25.9 at this URL: http://jsticca.wordpress.com/2009/09/01/the-magn | text | null |
L_0765 | generating and using electricity | T_3906 | The device in the circuit in Figure 25.9 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, this would increase the strength of the magnetic field as well. If the magnet were moved back and forth repeatedly, the current would keep changing direction. In other words, alternating current would be produced. This is illustrated in Figure 25.10. | text | null |
L_0765 | generating and using electricity | T_3907 | 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. | text | null |
L_0765 | generating and using electricity | T_3908 | An electric generator is a device that changes kinetic energy to electrical energy through electromagnetic induction. A simple diagram of an electric generator is shown in Figure 25.11. In a generator, some form of energy is applied to turn a shaft. This causes a coil of wire to rotate between opposite poles of a magnet. Because the coil is rotating in a magnetic field, electric current is generated in the wire. If the diagram in Figure 25.11 looks familiar to you, thats because a generator is an electric motor in reverse. Look back at the electric motor in Figure 25.8. If you were to mechanically turn the shaft of the motor (instead of using electromagnetism to turn it), the motor would generate electricity just like an electric generator. You can learn how to make a very simple electric generator by watching the video at the URL below. Making your own generator will help you understand how a generator works. Generators may be set up to produce either alternating or direct current. Generators in cars and most power plants produce alternating current. A car generator produces electricity with some of the kinetic energy of the turning crankshaft. The electricity is used to run the cars lights, power windows, radio, and other electric devices. Some of the electricity is stored in the cars battery to provide electrical energy when the car isnt running. A power plant generator produces electricity with the kinetic energy of a turning turbine. The energy to turn the turbine may come from burning fuel, falling water, or some other energy source. You can see how falling water is used to generate electricity in Figure 25.12 and in the video at this URL: | text | null |
L_0765 | generating and using electricity | T_3908 | An electric generator is a device that changes kinetic energy to electrical energy through electromagnetic induction. A simple diagram of an electric generator is shown in Figure 25.11. In a generator, some form of energy is applied to turn a shaft. This causes a coil of wire to rotate between opposite poles of a magnet. Because the coil is rotating in a magnetic field, electric current is generated in the wire. If the diagram in Figure 25.11 looks familiar to you, thats because a generator is an electric motor in reverse. Look back at the electric motor in Figure 25.8. If you were to mechanically turn the shaft of the motor (instead of using electromagnetism to turn it), the motor would generate electricity just like an electric generator. You can learn how to make a very simple electric generator by watching the video at the URL below. Making your own generator will help you understand how a generator works. Generators may be set up to produce either alternating or direct current. Generators in cars and most power plants produce alternating current. A car generator produces electricity with some of the kinetic energy of the turning crankshaft. The electricity is used to run the cars lights, power windows, radio, and other electric devices. Some of the electricity is stored in the cars battery to provide electrical energy when the car isnt running. A power plant generator produces electricity with the kinetic energy of a turning turbine. The energy to turn the turbine may come from burning fuel, falling water, or some other energy source. You can see how falling water is used to generate electricity in Figure 25.12 and in the video at this URL: | text | null |
L_0765 | generating and using electricity | T_3909 | An electric transformer is a device that uses electromagnetic induction to change the voltage of electric current. A transformer may either increase or decrease voltage, but it only works with alternating current. You can see the components of an electric transformer in Figure 25.13. As you can see in Figure 25.13, a transformer consists of two wire coils wrapped around an iron core. When alternating primary 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 changing magnetic field induces alternating current in coil S, which is part of another circuit. In Figure 25.13, coil P and coil S have the same number of turns of wire. In this case, the voltages of the primary and secondary currents are the same. However, when the two coils have different numbers of turns, the voltage of the secondary current is different than the voltage of the primary current. Both cases are illustrated in Figure 25.14. When coil S has more turns of wire than coil P, the voltage in the secondary current is greater than the voltage in the primary current. This type of transformer is called a step-up transformer. 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. This type of transformer is called a step-down transformer. For an animation of a transformer, go to this URL: . | text | null |
L_0765 | generating and using electricity | T_3910 | Power plant generators produce high-voltage electric current. Many power plants also use step-up transformers to increase the voltage of the current even more (see Figure 25.15). By increasing the voltage, the amount of current is decreased, so less power is lost as the electricity travels through the power lines. However, the voltage in power lines is too high to be safe for home circuits. The voltage in power lines may be as great as 750,000 volts, whereas most home circuits are 240 or 120 volts. One or more step-down transformers decrease the voltage of current before it enters the home. Other step-down transformers within the home lower the voltage of some of the homes circuits. For an overview of electric power generation, transmission, and distribution in the U.S., go to this URL: http://w | text | null |
L_0765 | generating and using electricity | T_3910 | Power plant generators produce high-voltage electric current. Many power plants also use step-up transformers to increase the voltage of the current even more (see Figure 25.15). By increasing the voltage, the amount of current is decreased, so less power is lost as the electricity travels through the power lines. However, the voltage in power lines is too high to be safe for home circuits. The voltage in power lines may be as great as 750,000 volts, whereas most home circuits are 240 or 120 volts. One or more step-down transformers decrease the voltage of current before it enters the home. Other step-down transformers within the home lower the voltage of some of the homes circuits. For an overview of electric power generation, transmission, and distribution in the U.S., go to this URL: http://w | text | null |
L_0766 | properties of matter | T_3911 | Both you and the speck of dust consist of atoms 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 arent matter are forms of energy, 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. | text | null |
L_0766 | properties of matter | T_3912 | Mass is the amount of matter in a substance or object. Mass is commonly measured with a balance. A simple mechanical balance is shown in Figure 3.1. It allows an object to be matched with other objects of known mass. SI units for mass are the kilogram, but for smaller masses grams are often used instead. | text | null |
L_0766 | properties of matter | T_3913 | The more matter an object contains, generally the more it weighs. However, weight is not the same thing as mass. Weight is a measure of the force of gravity pulling on an object. It is measured with a scale, like the kitchen- scale in Figure 3.2. The scale detects how forcefully objects in the pan are being pulled downward by the force of gravity. The SI unit for weight is the newton (N). The common English unit is the pound (lb). With Earths gravity, a mass of 1 kg has a weight of 9.8 N (2.2 lb). Problem Solving Problem: At Earths gravity, what is the weight in newtons of an object with a mass of 10 kg? Solution: At Earths gravity, 1 kg has a weight of 9.8 N. Therefore, 10 kg has a weight of (10 9.8 N) = 98 N. You Try It! Problem: 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, so mass and weight are closely related. However, the weight of an object can change if the force of gravity changes, even while the mass of the object remains constant. Look at the photo of astronaut Edwin E. Aldrin Jr taken by fellow astronaut Neil Armstrong, the first human to walk on the moon, in Figure 3.3. An astronaut weighed less on the moon than he did on Earth 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. 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 w h). For solids that have irregular shapes, the displacement method is used to measure volume. You can see how it works in Figure 3.4 and 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. | text | null |
L_0766 | properties of matter | T_3913 | The more matter an object contains, generally the more it weighs. However, weight is not the same thing as mass. Weight is a measure of the force of gravity pulling on an object. It is measured with a scale, like the kitchen- scale in Figure 3.2. The scale detects how forcefully objects in the pan are being pulled downward by the force of gravity. The SI unit for weight is the newton (N). The common English unit is the pound (lb). With Earths gravity, a mass of 1 kg has a weight of 9.8 N (2.2 lb). Problem Solving Problem: At Earths gravity, what is the weight in newtons of an object with a mass of 10 kg? Solution: At Earths gravity, 1 kg has a weight of 9.8 N. Therefore, 10 kg has a weight of (10 9.8 N) = 98 N. You Try It! Problem: 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, so mass and weight are closely related. However, the weight of an object can change if the force of gravity changes, even while the mass of the object remains constant. Look at the photo of astronaut Edwin E. Aldrin Jr taken by fellow astronaut Neil Armstrong, the first human to walk on the moon, in Figure 3.3. An astronaut weighed less on the moon than he did on Earth 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. 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 w h). For solids that have irregular shapes, the displacement method is used to measure volume. You can see how it works in Figure 3.4 and 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. | text | null |
L_0766 | properties of matter | T_3914 | Matter has many properties. Some are physical properties. Physical properties of matter are properties that can be measured or observed without matter changing to a different substance. For example, whether a given substance normally exists as a solid, liquid, or gas is a physical property. Consider water. It is a liquid at room temperature, but if it freezes and changes to ice, it is still water. Generally, physical properties are things you can see, hear, smell, or feel with your senses. | text | null |
L_0766 | properties of matter | T_3915 | Physical properties include the state of matter and its color and odor. For example, oxygen is a colorless, odorless gas. Chlorine is a greenish gas with a strong, sharp odor. Other physical properties include hardness, freezing and boiling points, the ability to dissolve in other substances, and the ability to conduct heat or electricity. These properties are demonstrated in Figure 3.5. Can you think of other physical properties? | text | null |
L_0766 | properties of matter | T_3916 | Density is an important physical property of matter. It reflects how closely packed the particles of matter are. Density is calculated from the amount of mass in a given volume of matter, using the formula: Density (D) = Mass (M) Volume (V ) Problem Solving Problem: What is the density of a substance that has a mass of 20 g and a volume of 10 mL? Solution: D = 20 g/10 mL = 2.0 g/mL You Try It! Problem: An object has a mass of 180 kg and a volume of 90 m3 . What is its density? To better understand density, think about a bowling ball and a volleyball. The bowling ball feels heavy. It is solid all the way through. It contains a lot of tightly packed particles of matter. In contrast, the volleyball feels light. It is full of air. It contains fewer, more widely spaced particles of matter. Both balls have about the same volume, but the bowling ball has a much greater mass. Its matter is denser. | text | null |
L_0766 | properties of matter | T_3917 | It looks like frozen smoke, and its the lightest solid material on the planet. Aerogel insulates space suits, makes tennis rackets stronger and could be used one day to clean up oil spills. Lawrence Livermore National Laboratory scientist Alex Gash shows us some remarkable properties of this truly unique substance. For more information on aerogel, see http://science.kqed.org/quest/video/quest-lab-aerogel/ . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0766 | properties of matter | T_3918 | Some properties of matter can be measured or observed only when matter undergoes a change to become an entirely different substance. These properties are called chemical properties. They include flammability and reactivity. | text | null |
L_0766 | properties of matter | T_3919 | Flammability is the ability of matter to burn. Wood is flammable; iron is not. When wood burns, it changes to ashes, carbon dioxide, water vapor, and other gases. After burning, it is no longer wood. | text | null |
L_0766 | properties of matter | T_3920 | Reactivity is the ability of matter to combine chemically with other substances. For example, iron is highly reactive with oxygen. When it combines with oxygen, it forms the reddish powder called rust (see Figure 3.6). Rust is not iron but an entirely different substance that consists of both iron and oxygen. | text | null |
L_0768 | changes in matter | T_3932 | A physical change in matter is a change in one or more of matters physical properties. Glass breaking is just one example of a physical change. Some other examples are shown in Figure 3.16 and in the video below. In each example, matter may look different after the change occurs, but its still the same substance with the same chemical properties. For example, smaller pieces of wood have the ability to burn just as larger logs do. MEDIA Click image to the left or use the URL below. URL: Because the type of matter remains the same with physical changes, the changes are often easy to undo. For example, braided hair can be unbraided again. Melted chocolate can be put in a fridge to re-harden. Dissolving salt in water is also a physical change. How do you think you could undo it? | text | null |
L_0768 | changes in matter | T_3933 | Did you ever make a "volcano," like the one in Figure 3.17, using baking soda and vinegar? What happens when the two substances combine? They produce an eruption of foamy bubbles. This happens because of a chemical change. A chemical change occurs when matter changes chemically into an entirely different substance with different chemical properties. When vinegar and baking soda combine, they form carbon dioxide, a gas that causes the bubbles. Its the same gas that gives soft drinks their fizz. Not all chemical changes are as dramatic as this "volcano." Some are slower and less obvious. Figure 3.18 and the video below show other examples of chemical changes. MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0768 | changes in matter | T_3934 | How can you tell whether a chemical change has occurred? Often, there are clues. Several are demonstrated in Figures 3.17 and 3.18 and in the video below. MEDIA Click image to the left or use the URL below. URL: To decide whether a chemical change has occurred, look for these signs: Gas bubbles are released. (Example: Baking soda and vinegar mix and produce bubbles.) Something changes color. (Example: Leaves turn from green to other colors.) An odor is produced. (Example: Logs burn and smell smoky.) A solid comes out of a solution. (Example: Eggs cook and a white solid comes out of the clear liquid part of the egg.) | text | null |
L_0768 | changes in matter | T_3935 | Because chemical changes produce new substances, they often cannot be undone. For example, you cant change a fried egg back to a raw egg. Some chemical changes can be reversed, but only by other chemical changes. For example, to undo the tarnish on copper pennies, you can place them in vinegar. The acid in the vinegar reacts with the tarnish. This is a chemical change that makes the pennies bright and shiny again. You can try this yourself at home to see how well it works. | text | null |
L_0768 | changes in matter | T_3936 | If you build a campfire, like the one in Figure 3.19, you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening, all thats left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the flames? It may seem that way, but in fact, the same amount of matter still exists. The wood changed not only to ashes but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes. Assume you had measured the mass of the wood before you burned it. Assume you had also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined have the same mass as the wood you started with. This example illustrates the law of conservation of mass. The law states that matter cannot be created or destroyed. Even when matter goes through physical or chemical changes, the total mass of matter always remains the same. (In the chapter Nuclear Chemistry, you will learn about nuclear reactions, in which mass is converted into energy. But other than that, the law of conservation of mass holds.) For a fun challenge, try to apply the law of conservation of mass to a scene from a Harry Potter film at this link: . | text | null |
L_0769 | solids liquids gases and plasmas | T_3937 | Ice is an example of solid matter. A solid is matter that has a fixed volume and a fixed shape. Figure 4.3 shows examples of matter that are usually solids under Earth conditions. In the figure, salt and cellulose are examples of crystalline solids. The particles of crystalline solids are arranged in a regular repeating pattern. The steaks and candle wax are examples of amorphous ("shapeless") solids. Their particles have no definite pattern. | text | null |
L_0769 | solids liquids gases and plasmas | T_3938 | Ocean water is an example of a liquid. A liquid is matter that has a fixed volume but not a fixed shape. Instead, a liquid takes the shape of its container. If the volume of a liquid is less than the volume of its container, the top surface will be exposed to the air, like the oil in the bottles in Figure 4.4. Two interesting 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 those in Figure 4.5. Viscosity is a liquids resistance to flowing. Thicker liquids are more viscous than thinner liquids. For example, the honey in Figure 4.5 is more viscous than the vinegar. You can learn more about surface tension and viscosity at these URLs: http://io9.com/5668221/an-experiment-with-soap-water-pepper-and-surface-tension http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Viscosity-840.html (1:40) MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0769 | solids liquids gases and plasmas | T_3938 | Ocean water is an example of a liquid. A liquid is matter that has a fixed volume but not a fixed shape. Instead, a liquid takes the shape of its container. If the volume of a liquid is less than the volume of its container, the top surface will be exposed to the air, like the oil in the bottles in Figure 4.4. Two interesting 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 those in Figure 4.5. Viscosity is a liquids resistance to flowing. Thicker liquids are more viscous than thinner liquids. For example, the honey in Figure 4.5 is more viscous than the vinegar. You can learn more about surface tension and viscosity at these URLs: http://io9.com/5668221/an-experiment-with-soap-water-pepper-and-surface-tension http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Viscosity-840.html (1:40) MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0769 | solids liquids gases and plasmas | T_3939 | Water vapor is an example of a gas. A gas is matter that has neither a fixed volume nor a fixed shape. Instead, a gas takes both the volume and the shape of its container. It spreads out to take up all available space. You can see an example in Figure 4.6. | text | null |
L_0769 | solids liquids gases and plasmas | T_3940 | Youre probably less familiar with plasmas than with solids, liquids, and gases. Yet, most of the universe consists of plasma. Plasma is a state of matter that resembles a gas but has certain properties that a gas does not have. Like a gas, plasma lacks a fixed volume and shape. Unlike a gas, plasma can conduct electricity and respond to magnetism. Thats because plasma contains charged particles called ions. This gives plasma other interesting properties. For example, it glows with light. Where can you find plasmas? Two examples are shown in Figure 4.7. The sun and other stars consist of plasma. Plasmas are also found naturally in lightning and the polar auroras (northern and southern lights). Artificial plasmas are found in fluorescent lights, plasma TV screens, and plasma balls like the one that opened this chapter. You can learn more about plasmas at this URL: (2:58). MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0769 | solids liquids gases and plasmas | T_3941 | Why do different states of matter have different properties? Its because of differences in energy at the level of atoms and molecules, the tiny particles that make up matter. | text | null |
L_0769 | solids liquids gases and plasmas | T_3942 | Energy is defined as the ability to cause changes in matter. You can change energy from one form to another when you lift your arm or take a step. In each case, energy is used to move matter you. The energy of moving matter is called kinetic energy. | text | null |
L_0769 | solids liquids gases and plasmas | T_3943 | The particles that make up matter are also constantly moving. They have kinetic energy. The theory that all matter consists of constantly moving particles is called the kinetic theory of matter. You can learn more about it at the URL below. | text | null |
L_0769 | solids liquids gases and plasmas | T_3944 | Particles of matter of the same substance, such as the same element, are attracted to one another. The force of attraction tends to pull the particles closer together. The particles need a lot of kinetic energy to overcome the force of attraction and move apart. Its like a tug of war between opposing forces. The kinetic energy of individual particles is on one side, and the force of attraction between different particles is on the other side. The outcome of the "war" depends on the state of matter. This is illustrated in Figure 4.8 and in the animation at this URL: http://w In solids, particles dont have enough kinetic energy to overcome the force of attraction between them. The particles are packed closely together and cannot move around. All they can do is vibrate. This explains why solids have a fixed volume and shape. In liquids, particles have enough kinetic energy to partly overcome the force of attraction between them. They can slide past one another but not pull completely apart. This explains why liquids can change shape but have a fixed volume. In gases, particles have a lot of kinetic energy. They can completely overcome the force of attraction between them and move apart. This explains why gases have neither a fixed volume nor a fixed shape. | text | null |
L_0771 | changes of state | T_3950 | What causes clouds to form? And in general, how does matter change from one state to another? As you may have guessed, changes in energy are involved. | text | null |
L_0771 | changes of state | T_3951 | Changes of state are physical changes in matter. They are reversible changes that do not involve changes in matters chemical makeup or chemical properties. Common changes of state include melting, freezing, sublimation, deposition, condensation, and vaporization. These changes are shown in Figure 4.18. Each is described in detail below. | text | null |
L_0771 | changes of state | T_3952 | Energy is always involved in changes of state. Matter either loses or absorbs energy when it changes from one state to another. For example, when matter changes from a liquid to a solid, it loses energy. The opposite happens when matter changes from a solid to a liquid. For a solid to change to a liquid, matter must absorb energy from its surroundings. The amount of energy in matter can be measured with a thermometer. Thats because a thermometer measures temperature, and temperature is the average kinetic energy of the particles of matter. You can learn more about energy, temperature, and changes of state at this URL: http://hogan.chem.lsu.edu/matter/chap26/animate3/an2 | text | null |
L_0771 | changes of state | T_3953 | Think about how you would make ice cubes in a tray. First you would fill the tray with water from a tap. Then you would place the tray in the freezer compartment of a refrigerator. The freezer is very cold. What happens next? | text | null |
L_0771 | changes of state | T_3954 | The warmer water in the tray loses heat to the colder air in the freezer. The water cools until its particles no longer have enough energy to slide past each other. Instead, they remain in fixed positions, locked in place by the forces of attraction between them. The liquid water has changed to solid ice. Another example of liquid water changing to solid ice is pictured in Figure 4.19. The process in which a liquid changes to a solid is called freezing. The temperature at which a liquid changes to a solid is its freezing point. The freezing point of water is 0C (32F). Other types of matter may have higher or lower freezing points. For example, the freezing point of iron is 1535C. The freezing point of oxygen is -219C. | text | null |
L_0771 | changes of state | T_3955 | If you took ice cubes out of a freezer and left them in a warm room, the ice would absorb energy from the warmer air around it. The energy would allow the particles of frozen water to overcome some of the forces of attraction holding them together. They would be able to slip out of the fixed positions they held as ice. In this way, the solid ice would turn to liquid water. The process in which a solid changes to a liquid is called melting. The melting point is the temperature at which a solid changes to a liquid. For a given type of matter, the melting point is the same as the freezing point. What is the melting point of ice? What is the melting point of iron, pictured in Figure 4.20? | text | null |
L_0771 | changes of state | T_3956 | If you fill a pot with cool tap water and place the pot on a hot stovetop, the water heats up. Heat energy travels from the stovetop to the pot, and the water absorbs the energy from the pot. What happens to the water next? | text | null |
L_0771 | changes of state | T_3957 | If water gets hot enough, it starts to boil. Bubbles of water vapor form in boiling water. This happens as particles of liquid water gain enough energy to completely overcome the force of attraction between them and change to the gaseous state. The bubbles rise through the water and escape from the pot as steam. The process in which a liquid boils and changes to a gas is called vaporization. The temperature at which a liquid boils is its boiling point. The boiling point of water is 100C (212F). Other types of matter may have higher or lower boiling points. For example, the boiling point of table salt is 1413C. The boiling point of nitrogen is -196C. | text | null |
L_0771 | changes of state | T_3958 | A liquid can also change to a gas without boiling. This process is called evaporation. It occurs when particles at the exposed surface of a liquid absorb just enough energy to pull away from the liquid and escape into the air. This happens faster at warmer temperatures. Look at the puddle in Figure 4.21. It formed in a pothole during a rain shower. The puddle will eventually evaporate. It will evaporate faster if the sun comes out and heats the water than if the sky remains cloudy. | text | null |
L_0771 | changes of state | T_3959 | If you take a hot shower in a closed bathroom, the mirror is likely to "fog" up. The "fog" consists of tiny droplets of water that form on the cool surface of the mirror. Why does this happen? Some of the hot water from the shower evaporates, so the air in the bathroom contains a lot of water vapor. When the water vapor contacts cooler surfaces, such as the mirror, it cools and loses energy. The cooler water particles no longer have enough energy to overcome the forces of attraction between them. They come together and form droplets of liquid water. The process in which a gas changes to a liquid is called condensation. Other examples of condensation are shown in Figure 4.22. A gas condenses when it is cooled below its boiling point. At what temperature does water vapor condense? | text | null |
L_0771 | changes of state | T_3959 | If you take a hot shower in a closed bathroom, the mirror is likely to "fog" up. The "fog" consists of tiny droplets of water that form on the cool surface of the mirror. Why does this happen? Some of the hot water from the shower evaporates, so the air in the bathroom contains a lot of water vapor. When the water vapor contacts cooler surfaces, such as the mirror, it cools and loses energy. The cooler water particles no longer have enough energy to overcome the forces of attraction between them. They come together and form droplets of liquid water. The process in which a gas changes to a liquid is called condensation. Other examples of condensation are shown in Figure 4.22. A gas condenses when it is cooled below its boiling point. At what temperature does water vapor condense? | text | null |
L_0771 | changes of state | T_3960 | Solids that change to gases generally first pass through the liquid state. However, sometimes solids change directly to gases and skip the liquid state. The reverse can also occur. Sometimes gases change directly to solids. | text | null |
L_0771 | changes of state | T_3961 | The process in which a solid changes directly to a gas is called sublimation. It occurs when the particles of a solid absorb enough energy to completely overcome the force of attraction between them. Dry ice (solid carbon dioxide, CO2 ) is an example of a solid that undergoes sublimation. Figure 4.23 shows a chunk of dry ice changing directly to carbon dioxide gas. Sometimes snow undergoes sublimation as well. This is most likely to occur on sunny winter days when the air is very dry. What gas does snow become? | text | null |
L_0771 | changes of state | T_3962 | The opposite of sublimation is deposition. This is the process in which a gas changes directly to a solid without going through the liquid state. It occurs when gas particles become very cold. For example, when water vapor in the air contacts a very cold windowpane, the water vapor may change to tiny ice crystals on the glass. The ice crystals are called frost. You can see an example in Figure 4.24. | text | null |
L_0805 | atoms | T_4146 | Identify the conditions that will speed up or slow down the dissolving process. | text | null |
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