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_0805 | atoms | T_4147 | Did you ever drink the tea before all the sugar has dissolved? Did you ever notice that some of the sugar is sitting at the bottom of the glass? Q: What could you do to dissolve the sugar faster? A: The rate of dissolving is caused by several factors. These factors include stirring, temperature, and the size of the particles. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0805 | atoms | T_4148 | What would happen if you added sugar to iced tea and did not stir the liquid? Thats right, most of the sugar you added would fall to the bottom of the glass. Like most people, when you add sugar to a liquid, you stir it, but why? For most of us, it is automatic. How many times have you added something to a liquid and immediately grabbed our spoon and started to stir. Have you ever thought about why we stir? So, why do we stir liquids when we add other ingredients? Stirring a liquid while you are mixing in another ingredient speeds up the rate of dissolving. This is because it helps distribute the particles that are being dissolved. What happens when you add sugar (the solute) to iced tea (the solvent) and then stir the tea? The obvious answer is that the sugar will dissolve. The more quickly you stir, the faster the sugar will dissolve. What if you dont stir the tea? Will the sugar still dissolve? It may eventually dissolve, but it will take much longer. You can think of stirring like adding energy to the process. What are other ways to add energy? | text | null |
L_0805 | atoms | T_4149 | What do you think will happen when you add the same amount of sugar to cups of hot and cold tea? Will the sugar dissolve at the same rate? Is that why people start with warm water when they make iced tea? The temperature of the solvent is an important factor in how fast something dissolves. Temperature affects how fast a solute dissolves. Generally, a solute dissolves faster in a warmer solvent. It dissolves more slowly in a cooler solvent. Think about that next time you make iced tea. | text | null |
L_0805 | atoms | T_4150 | There is another factor that affects the rate of dissolving. The particle size of solute particles affects the rate. Smaller particles have greater surface area. Think of a large block of Legos. When all the blocks are stuck together you can measure their surface area. Now take all the blocks apart and measure their individual surface areas. Which has more? Greater surface area provides more contact between the particles and the solvent. For example, if you put granulated sugar in a glass of iced tea, it will dissolve more quickly. If you put a sugar cube in a glass of iced tea, it will dissolve more slowly. Thats because all those tiny particles of granulated sugar have greater surface area than a single sugar cube. | text | null |
L_0805 | atoms | T_4151 | 1. List three factors that affect the rate at which a solute dissolves in a solvent. 2. Gina is trying to dissolve bath salts in her bathwater. How could she speed up the rate of dissolving? | text | null |
L_0805 | atoms | T_4152 | 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_0812 | boiling | T_4173 | Steam actually consists of tiny droplets of liquid water. What you cant see in the picture is the water vapor that is also present in the air above the spring. Water vapor is water in the gaseous state. It constantly rises up from the surface of boiling hot water. Why? At high temperatures, particles of a liquid gain enough energy to completely overcome the force of attraction between them, so they change to a gas. The gas forms bubbles that rise to the surface of the liquid because gas is less dense than liquid. The bubbling up of the liquid is called boiling. When the bubbles reach the surface, the gas escapes into the air. The entire process in which a liquid boils and changes to a gas that escapes into the air is called vaporization. Q: Why does steam form over the hot spring pictured above? A: Steam forms when some of the water vapor from the boiling water cools in the air and condenses to form droplets of liquid water. | text | null |
L_0812 | boiling | T_4174 | Vaporization is easily confused with evaporation, but the two processes are not the same. Evaporation also changes a liquid to a gas, but it doesnt involve boiling. Instead, evaporation occurs when particles at the surface of a liquid gain enough energy to escape into the air. This happens without the liquid becoming hot enough to boil. | text | null |
L_0812 | boiling | T_4175 | The temperature at which a substance boils and changes to a gas is called its boiling point. Boiling point is a physical property of matter. The boiling point of pure water is 100 C. Other substances may have higher or lower boiling points. Several examples are listed in the Table 1.1. Pure water is included in the table for comparison. Substance Hydrogen Nitrogen Carbon dioxide Ammonia Pure water Salty ocean water Petroleum Olive oil Sodium chloride Boiling Point ( C) -253 -196 -79 -36 100 101 210 300 1413 Q: Assume you want to get the salt (sodium chloride) out of salt water. Based on information in the table, how could you do it? A: You could heat the salt water to 101 C. The water would boil and vaporize but the salt would not. Instead, the salt would be left behind as solid particles. Q: Oxygen is a gas at room temperature (20 C). What does this tell you about its boiling point? A: The boiling point of oxygen must be lower than 20 C. Otherwise, it would be a liquid at room temperature. | text | null |
L_0818 | calculating derived quantities | T_4190 | Derived quantities are quantities that are calculated from two or more measurements. Derived quantities cannot be measured directly. They can only be computed. Many derived quantities are calculated in physical science. Three examples are area, volume, and density. | text | null |
L_0818 | calculating derived quantities | T_4191 | The area of a surface is how much space it covers. Its easy to calculate the area of a surface if it has a regular shape, such as the blue rectangle in the sketch below. You simply substitute measurements of the surface into the correct formula. To find the area of a rectangular surface, use this formula: Area (rectangular surface) = length width (l w) Q: What is the area of the blue rectangle? A: Substitute the values for the rectangles length and width into the formula for area: Area = 9 cm 5 cm = 45 cm2 Q: Can you use this formula to find the area of a square surface? A: Yes, you can. A square has four sides that are all the same length, so you would substitute the same value for both length and width in the formula for the area of a rectangle. | text | null |
L_0818 | calculating derived quantities | T_4192 | The volume of a solid object is how much space it takes up. Its easy to calculate the volume of a solid if it has a simple, regular shape, such as the rectangular solid pictured in the sketch below. To find the volume of a rectangular solid, use this formula: Volume (rectangular solid) = length width height (l w h) Q: What is the volume of the blue rectangular solid? A: Substitute the values for the rectangular solids length, width, and height into the formula for volume: Volume = 10 cm 3 cm 5 cm = 150 cm3 | text | null |
L_0818 | calculating derived quantities | T_4193 | Density is a quantity that expresses how much matter is packed into a given space. The amount of matter is its mass, and the space it takes up is its volume. To calculate the density of an object, then, you would use this formula: Density = mass volume Q: The volume of the blue rectangular solid above is 150 cm3 . If it has a mass of 300 g, what is its density? A: The density of the rectangular solid is: Density = 300 g = 2 g/cm3 150 cm3 Q: Suppose you have two boxes that are the same size but one box is full of feathers and the other box is full of books. Which box has greater density? A: Both boxes have the same volume because they are the same size. However, the books have greater mass than the feathers. Therefore, the box of books has greater density. | text | null |
L_0818 | calculating derived quantities | T_4194 | A given derived quantity, such as area, is always expressed in the same type of units. For example, area is always expressed in squared units, such as cm2 or m2 . If you calculate area and your answer isnt in squared units, then you have made an error. Q: What units are used to express volume? A: Volume is expressed in cubed units, such as cm3 or m3 . Q: A certain derived quantity is expressed in the units kg/m3 . Which derived quantity is it? A: The derived quantity is density, which is mass (kg) divided by volume (m3 ). | text | null |
L_0825 | changes of state | T_4214 | The water droplets of fog form from water vapor in the air. Fog disappears when the water droplets change back to water vapor. These changes are examples of changes of state. A change of state occurs whenever matter changes from one state to another. Common states of matter on Earth are solid, liquid, and gas. Matter may change back and forth between any two of these states. Changes of state are physical changes in matter. They are reversible changes that do not change matters chemical makeup or chemical properties. For example, when fog changes to water vapor, it is still water and can change back to liquid water again. | text | null |
L_0825 | changes of state | T_4215 | Several processes are involved in common changes of state. They include melting, freezing, sublimation, deposition, condensation, and evaporation. The Figure 1.1 shows how matter changes in each of these processes. Q: Which two processes result in matter changing to the solid state? A: The processes are deposition, in which matter changes from a gas to a solid, and freezing, in which matter changes from a liquid to a solid. | text | null |
L_0825 | changes of state | T_4216 | Suppose that you leave some squares of chocolate candy in the hot sun. A couple of hours later, you notice that the chocolate has turned into a puddle like the one pictured in the Figure 1.2. Q: What happened to the chocolate? A: The chocolate melted. It changed from a solid to a liquid. In order for solid chocolate to melt and change to a liquid, the particles of chocolate must gain energy. The chocolate pictured in the Figure 1.2 gained energy from sunlight. Energy is the ability to cause changes in matter, and it is always involved in changes of state. When matter changes from one state to another, it either absorbs energyas when chocolate meltsor loses energy. For example, if you were to place the melted chocolate in a refrigerator, it would lose energy to the cold air inside the refrigerator. As a result, the liquid chocolate would change to a solid Q: Why is energy always involved in changes of state? A: The energy of particles of matter determines the matters state. Particles of a gas have more energy than particles of a liquid, and particles of a liquid have more energy than particles of a solid. Therefore, in order for matter to change from a solid to a liquid or from a liquid to a gas, particles of matter must absorb energy. In order for matter to change from a gas to a liquid or from a liquid to a solid, particles of matter must lose energy. | text | null |
L_0825 | changes of state | T_4216 | Suppose that you leave some squares of chocolate candy in the hot sun. A couple of hours later, you notice that the chocolate has turned into a puddle like the one pictured in the Figure 1.2. Q: What happened to the chocolate? A: The chocolate melted. It changed from a solid to a liquid. In order for solid chocolate to melt and change to a liquid, the particles of chocolate must gain energy. The chocolate pictured in the Figure 1.2 gained energy from sunlight. Energy is the ability to cause changes in matter, and it is always involved in changes of state. When matter changes from one state to another, it either absorbs energyas when chocolate meltsor loses energy. For example, if you were to place the melted chocolate in a refrigerator, it would lose energy to the cold air inside the refrigerator. As a result, the liquid chocolate would change to a solid Q: Why is energy always involved in changes of state? A: The energy of particles of matter determines the matters state. Particles of a gas have more energy than particles of a liquid, and particles of a liquid have more energy than particles of a solid. Therefore, in order for matter to change from a solid to a liquid or from a liquid to a gas, particles of matter must absorb energy. In order for matter to change from a gas to a liquid or from a liquid to a solid, particles of matter must lose energy. | text | null |
L_0827 | chemical and solar cells | T_4218 | Chemical cells are found in batteries. They produce voltage by means of chemical reactions. Chemical cells have two electrodes, which are strips of different materials, such as zinc and carbon. The electrodes are suspended in an electrolyte. This is a substance that contains free ions, which 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. The Figure 1.1 shows how a battery works. The diagram represents the simplest type of battery, one that contains a single chemical cell. 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. Electrons flow through the electrolyte from the negative to positive electrode. The electrodes extend out of the battery for the attachment of wires that carry the current. The current can be used to power a light bulb or other electric device. | text | null |
L_0827 | chemical and solar cells | T_4219 | Solar cells convert the energy in sunlight to electrical energy. Solar cells are also called photovoltaic (PV) cells because they use light (photo-) to produce voltage (-voltaic). Solar cells contain a material such as silicon that absorbs light energy. The energy knocks electrons loose so they can flow freely and produce a difference in electric potential energy, or voltage. The flow of electrons creates electric current. Solar cells have positive and negative contacts, like the terminals in chemical cells. If the contacts are connected with wire, current flows from the negative to positive contact. The Figure 1.2 shows how a solar cell works. | text | null |
L_0827 | chemical and solar cells | T_4219 | Solar cells convert the energy in sunlight to electrical energy. Solar cells are also called photovoltaic (PV) cells because they use light (photo-) to produce voltage (-voltaic). Solar cells contain a material such as silicon that absorbs light energy. The energy knocks electrons loose so they can flow freely and produce a difference in electric potential energy, or voltage. The flow of electrons creates electric current. Solar cells have positive and negative contacts, like the terminals in chemical cells. If the contacts are connected with wire, current flows from the negative to positive contact. The Figure 1.2 shows how a solar cell works. | text | null |
L_0829 | chemical change | T_4223 | A chemical change occurs whenever matter changes into an entirely different substance with different chemical properties. A chemical change is also called a chemical reaction. Many complex chemical changes occur to produce the explosions of fireworks. An example of a simpler chemical change is the burning of methane. Methane is the main component of natural gas, which is burned in many home furnaces. During burning, methane combines with oxygen in the air to produce entirely different chemical substances, including the gases carbon dioxide and water vapor. Click image to the left or use the URL below. URL: | text | null |
L_0829 | chemical change | T_4224 | Most chemical changes are not as dramatic as exploding fireworks, so how can you tell whether a chemical change has occurred? There are usually clues. You just need to know what to look for. A chemical change has probably occurred if bubbles are released, there is a change of color, or an odor is produced. Other clues include the release of heat, light, or loud sounds. Examples of chemical changes that produce these clues are shown in the Figure 1.1. Q: In addition to iron rusting, what is another example of matter changing color? Do you think this color change is a sign that a new chemical substance has been produced? A: Another example of matter changing color is a penny changing from reddish brown to greenish brown as it becomes tarnished. The color change indicates that a new chemical substance has been produced. Copper on the surface of the penny has combined with oxygen in the air to produce a different substance called copper oxide. Q: Besides food spoiling, what is another change that produces an odor? Is this a chemical change? A: When wood burns, it produces a smoky odor. Burning is a chemical change. Q: Which signs of chemical change do fireworks produce? A: Fireworks produce heat, light, and loud sounds. These are all signs of chemical change. | text | null |
L_0829 | chemical change | T_4225 | Because chemical changes produce new substances, they often cannot be undone. For example, you cant change ashes from burning logs back into wood. Some chemical changes can be reversed, but only by other chemical changes. For example, to undo tarnish on copper pennies, you can place them in vinegar. The acid in the vinegar combines with the copper oxide of the tarnish. This changes the copper oxide back to copper and oxygen, making the pennies reddish brown again. You can try this at home to see how well it works. | text | null |
L_0832 | chemical properties of matter | T_4232 | Chemical properties are properties that can be measured or observed only when matter undergoes a change to become an entirely different kind of matter. For example, the ability of iron to rust can only be observed when iron actually rusts. When it does, it combines with oxygen to become a different substance called iron oxide. Iron is very hard and silver in color, whereas iron oxide is flakey and reddish brown. Besides the ability to rust, other chemical properties include reactivity and flammability. | text | null |
L_0832 | chemical properties of matter | T_4233 | Reactivity is the ability of matter to combine chemically with other substances. Some kinds of matter are extremely reactive; others are extremely unreactive. For example, potassium is very reactive, even with water. When a pea- sized piece of potassium is added to a small amount of water, it reacts explosively. You can observe this reaction in the video below. (Caution: Dont try this at home!) In contrast, noble gases such as helium almost never react with any other substances. Click image to the left or use the URL below. URL: | text | null |
L_0832 | chemical properties of matter | T_4234 | Flammability is the ability of matter to burn. When matter burns, it combines with oxygen and 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, whereas 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, as well as fuels made from petroleum, such as gasoline and kerosene. Substances made of wood, such as paper and cardboard, are also flammable. | text | null |
L_0842 | condensation | T_4266 | The drops of water on the spider web are dewdrops. They formed overnight when warm moist air came into contact with the cooler spider web. Contact with the cooler web cooled the air. When air cools, it can hold less water vapor, so some of the water vapor in the air changed to liquid water. The process in which water vaporor another gaschanges to a liquid is called condensation. Another common example of condensation is pictured in the Figure 1.1. | text | null |
L_0842 | condensation | T_4267 | When air is very humid, it doesnt have to cool very much for water vapor in the air to start condensing. The temperature at which condensation occurs is called the dew point. The dew point varies depending on air temperature and moisture content. It is always less than or equal to the actual air temperature, but warmer air and moister air have dew points closer to the actual air temperature. Thats why glasses of cold drinks sweat more on a hot, humid day than they do on a cool, dry day. Q: What happens when air temperature reaches the dew point? A: When air temperature reaches the dew point, water vapor starts condensing. It may form dew (as on the spider web in the opening image), clouds, or fog. Dew forms on solid objects on the ground. Clouds form on tiny particles in the air high above the ground. Fog is a cloud that forms on tiny particles in the air close to the ground. | text | null |
L_0842 | condensation | T_4267 | When air is very humid, it doesnt have to cool very much for water vapor in the air to start condensing. The temperature at which condensation occurs is called the dew point. The dew point varies depending on air temperature and moisture content. It is always less than or equal to the actual air temperature, but warmer air and moister air have dew points closer to the actual air temperature. Thats why glasses of cold drinks sweat more on a hot, humid day than they do on a cool, dry day. Q: What happens when air temperature reaches the dew point? A: When air temperature reaches the dew point, water vapor starts condensing. It may form dew (as on the spider web in the opening image), clouds, or fog. Dew forms on solid objects on the ground. Clouds form on tiny particles in the air high above the ground. Fog is a cloud that forms on tiny particles in the air close to the ground. | text | null |
L_0842 | condensation | T_4268 | The water cycle continuously recycles Earths water. Condensation plays an important role in this cycle. Find condensation in the water cycle Figure 1.3. It changes water vapor in the atmosphere to liquid water that can fall to Earth again. Without condensation, the water cycle would be interrupted and Earths water could not recycle. Q: In the water cycle, what happens to water after it condenses? A: After water condenses, it may form clouds that produce precipitation such as rain. | text | null |
L_0844 | conservation of mass | T_4271 | It may seem as though burning destroys matter, but the same amount, or mass, of matter still exists after a campfire as before. Look at the sketch in Figure 1.1. It shows that when wood burns, it combines with oxygen and changes not only to ashes but also to carbon dioxide and water vapor. The gases float off into the air, leaving behind just the ashes. Suppose you had measured the mass of the wood before it burned and the mass of the ashes after it burned. Also suppose you had been able to measure the oxygen used by the fire and the gases produced by the fire. What would you find? The total mass of matter after the fire would be the same as the total mass of matter before the fire. Q: What can you infer from this example? A: You can infer that burning does not destroy matter. It just changes matter into different substances. | text | null |
L_0844 | conservation of mass | T_4272 | This burning campfire example illustrates a very important law in science: the law of conservation of mass. This law states that matter cannot be created or destroyed. Even when matter goes through a physical or chemical change, the total mass of matter always remains the same. Q: How could you show that the mass of matter remains the same when matter changes state? A: You could find the mass of a quantity of liquid water. Then you could freeze the water and find the mass of the ice. The mass before and after freezing would be the same, showing that mass is conserved when matter changes state. | text | null |
L_0855 | density | T_4306 | Density is an important physical property of matter. It reflects how closely packed the particles of matter are. When particles are packed together more tightly, matter has greater density. Differences in density of matter explain many phenomena, not just why helium balloons rise. For example, differences in density of cool and warm ocean water explain why currents such as the Gulf Stream flow through the oceans. 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 are about the same size, but the bowling ball feels much heavier than the volleyball. Thats because the bowling ball is made of solid plastic, which contains a lot of tightly packed particles of matter. The volleyball, in contrast, is full of air, which contains fewer, more widely spaced particles of matter. In other words, the matter inside the bowling ball is denser than the matter inside the volleyball. Q: If you ever went bowling, you may have noticed that some bowling balls feel heavier than others even though they are the same size. How can this be? A: Bowling balls that feel lighter are made of matter that is less dense. | text | null |
L_0855 | density | T_4307 | The density of matter is actually the amount of matter in a given space. The amount of matter is measured by its mass, and 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_0856 | deposition | T_4308 | Deposition refers to the process in which a gas changes directly to a solid without going through the liquid state. For example, when warm moist air inside a house comes into contact with a freezing cold windowpane, water vapor in the air changes to tiny ice crystals. The ice crystals are deposited on the glass, often in beautiful patterns like the leaves on the window above. Be aware that deposition has a different meaning in Earth science than in chemistry. In Earth science, deposition refers to the dropping of sediments by wind or water, rather than to a change of state. | text | null |
L_0856 | deposition | T_4309 | Deposition as a change of state often occurs in nature. For example, when warm moist air comes into contact with very cold surfacessuch as the ground or objects on the groundice crystals are deposited on them. These ice crystals are commonly called frost. Look at the dead leaf and blades of grass in the Figure 1.1. They are covered with frost. If you look closely, you can see the individual crystals of ice. You can watch a demonstration of frost forming on the side of a very cold can at the URL below. (Click on the mulitmedia choice Ice on a Can.). The ice in the can has been cooled to a very low temperature by adding salt to it. Q: In places with very cold winters, why might frost be more likely to form on the ground in the fall than in the winter? A: Frost forms when the air is warmer than the ground. This is more likely to be the case in the fall. In the winter, the air is likely to be as cold as the ground. Deposition also occurs high above the ground when water vapor in the air changes to ice crystals. In the atmosphere, the ice crystals are deposited on tiny dust particles. These ice crystals form clouds, generally cirrus clouds, which are thin and wispy. You can see cirrus clouds in the Figure 1.2. Q: Cirrus clouds form only at altitudes of 6 kilometers or higher above sea level. Do you know why? A: At this altitude, the atmosphere is always very cold. Unless the air is cold, water vapor will condense to form water droplets instead of ice crystals. | text | null |
L_0856 | deposition | T_4309 | Deposition as a change of state often occurs in nature. For example, when warm moist air comes into contact with very cold surfacessuch as the ground or objects on the groundice crystals are deposited on them. These ice crystals are commonly called frost. Look at the dead leaf and blades of grass in the Figure 1.1. They are covered with frost. If you look closely, you can see the individual crystals of ice. You can watch a demonstration of frost forming on the side of a very cold can at the URL below. (Click on the mulitmedia choice Ice on a Can.). The ice in the can has been cooled to a very low temperature by adding salt to it. Q: In places with very cold winters, why might frost be more likely to form on the ground in the fall than in the winter? A: Frost forms when the air is warmer than the ground. This is more likely to be the case in the fall. In the winter, the air is likely to be as cold as the ground. Deposition also occurs high above the ground when water vapor in the air changes to ice crystals. In the atmosphere, the ice crystals are deposited on tiny dust particles. These ice crystals form clouds, generally cirrus clouds, which are thin and wispy. You can see cirrus clouds in the Figure 1.2. Q: Cirrus clouds form only at altitudes of 6 kilometers or higher above sea level. Do you know why? A: At this altitude, the atmosphere is always very cold. Unless the air is cold, water vapor will condense to form water droplets instead of ice crystals. | text | null |
L_0858 | direct and alternating current | T_4313 | When current flows in just one direction, it is called direct current (DC). The diagram below shows how direct current flows through a simple circuit. An example of direct current is the current that flows through a battery- powered flashlight. In addition to batteries, solar cells and fuel cells can also provide direct current. | text | null |
L_0858 | direct and alternating current | T_4314 | When current keeps reversing direction, it is called alternating current (AC). You can see how it works in the two diagrams below. The current that comes from a power plant and supplies electricity to homes and businesses is alternating current. The current changes direction 60 times per second. It happens so quickly that the light bulb doesnt have a chance to stop glowing when the reversals occur. Q: Which type of current flows through the wires in your home? A: Alternating current from a power plant flows through the wires in a home. | text | null |
L_0860 | discovery of electromagnetism | T_4318 | Magnetism produced by electricity is called electromagnetism. Today, electromagnetism is used in many electric devices. However, until electromagnetism was discovered, scientists thought that electricity and magnetism were unrelated. A Danish scientist named Hans Christian Oersted (pictured in the Figure 1.1) changed all that. He made the important discovery that electric current creates a magnetic field. But like many other important discoveries in science, Oersteds discovery was just a lucky accident. | text | null |
L_0860 | discovery of electromagnetism | T_4319 | In 1820, Oersted was presenting a demonstration to some science students. Ironically, he was trying to show them that electricity and magnetism are not related. He placed a wire with electric current flowing through it next to a compass, which has a magnetic needle. As he expected, the needle of the compass didnt move. It just kept pointing toward Earths north magnetic pole. After the demonstration, a curious student held the wire near the compass again, but in a different direction. To Oersteds surprise, the needle of the compass swung toward the wire so it was no longer pointing north. Oersted was intrigued. He turned off the current in the wire to see what would happen to the compass needle. The needle swung back to its original position, pointing north once 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 needle of the nearby compass. | text | null |
L_0860 | discovery of electromagnetism | T_4320 | Oersted wanted to learn more about the magnetic field created by a current. He placed a compass at different locations around a wire with current flowing through it. You can see what he found in the Figure 1.2. The lines of magnetic force circle around the wire in a counterclockwise direction. | text | null |
L_0860 | discovery of electromagnetism | T_4321 | Just about a decade after Oersted discovered that electric current can produce a magnetic field, an English scientist named Michael Faraday discovered that the opposite is also true. A magnetic field can produce an electric current. This is known as Faradays law. The process by which a magnetic field produces current is called electromagnetic induction. It occurs when a conductor, such as a wire, crosses lines of force in a magnetic field. This can happen when a wire is moving relative to a magnet or a magnet is moving relative to a wire. | text | null |
L_0867 | electric charge and electric force | T_4338 | 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. In the Figure 1.1, you can see that positively charged protons (+) are located in the nucleus of the atom, while negatively charged electrons (-) move around the nucleus. | text | null |
L_0867 | electric charge and electric force | T_4339 | When it comes to electric charges, opposites attract, so positive and negative particles attract each other. You can see this in the Figure 1.2. This attraction explains why negative electrons keep moving around the positive nucleus of the atom. Like charges, on the other hand, repel each other, so two positive or two negative charges push apart. This is also shown in the diagram. The attraction or repulsion between charged particles is called electric force. The strength of electric force depends on the amount of electric charge on the particles and the distance between them. Larger charges or shorter distances result in greater force. Q: How do positive protons stay close together inside the nucleus of the atom if like charges repel each other? A: Other, stronger forces in the nucleus hold the protons together. | text | null |
L_0867 | electric charge and electric force | T_4339 | When it comes to electric charges, opposites attract, so positive and negative particles attract each other. You can see this in the Figure 1.2. This attraction explains why negative electrons keep moving around the positive nucleus of the atom. Like charges, on the other hand, repel each other, so two positive or two negative charges push apart. This is also shown in the diagram. The attraction or repulsion between charged particles is called electric force. The strength of electric force depends on the amount of electric charge on the particles and the distance between them. Larger charges or shorter distances result in greater force. Q: How do positive protons stay close together inside the nucleus of the atom if like charges repel each other? A: Other, stronger forces in the nucleus hold the protons together. | text | null |
L_0868 | electric circuits | T_4340 | 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. Home circuits generally have a safe upper limit of about 20 or 30 amps. | text | null |
L_0868 | electric circuits | T_4341 | All electric circuits have at least two parts: a voltage source and a conductor. They may have other parts as well, such as light bulbs and switches, as in the simple circuit seen in the Figure 1.1. The voltage source of this simple circuit 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 the Figure 1.1, the wires are connected to both terminals of the battery, so they form a closed loop. Most circuits have devices such as light bulbs that convert electrical energy to other forms of energy. In the case of a light bulb, electrical energy is converted to light and thermal energy. Many circuits have switches to control the flow of current. 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_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 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.