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11.1 Current, Potential Difference, and Resistance

Here is a summary of what you will learn in this section:

• An electrochemical cell generates a potential difference by creating an imbalance of charges between its terminals. • Potential difference is the difference in electric charge between two points that will cause current to flow in a closed circuit. • Current is the rate of movement of electrons through a conductor. • An electric circuit is a path along which electrons flow.

• Resistance is the ability of a material to resist the flow of electrons. • Resistance in a wire depends on wire length, material, temperature, and cross- sectional area.

Figure 11.1 The elephantnose fish has tiny electric sensors in its nose that help it find food.

Electric Fish, Eels, and Rays You probably know that when it comes to electrical safety, it is very important to keep electrical devices away from water. For some animals, this safety concern about electricity is not a problem. In fact, they survive because they can use electricity in the water. The elephantnose fish from central Africa has an extended nose that contains about 500 electric sensors (Figure 11.1) These sensors are used to help this tiny fish find food. The elephantnose fish hides for protection during the day and comes out to feed at night. The electric sensors help it find smaller living things crawling along the bottom of the river or swimming in the water. Research has shown that these electric sensors are so sensitive that they can detect chemical pollutants. Further research will Figure 11.2 The electric eel uses determine if this type of sensor can be used to monitor the levels electricity to defend itself and to stun its prey. of pollutants in rivers.

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The electric eel in Figure 11.2 lives in the murky waterways of the Amazon and Orinoco river basins of South America. It’s really a fish and not an eel, but it really is electric — and dangerous. The eel’s electricity comes from a special organ in its long tail that contains thousands of muscle cells that work like tiny batteries. Each cell can produce only a small amount of electricity, but by working together all the cells can produce controlled bursts of electricity equal to five times the energy of a standard wall socket. These electrical bursts are used to stun prey Figure 11.3 A Pacific electric ray can send out a powerful electric when the electric eel is hunting for food. Some electric eels also shock. generate an electric signal to attract a mate. The Pacific electric ray, found along the west coast of North America, has an electric organ located in its head (Figure 11.3). This organ can generate enough electricity to knock down a human. Other types of electric rays use these electric shocks for defense when they are attacked. Rays belong to a category of animals called Torpedo. The name for this category comes from the Latin word torpidus, which means numbness. This term describes what happens to a person who steps on an electric ray.

D12 Quick Lab Light the Lights

In this activity, you will use a combination of wires, Procedure light bulbs, and an electrochemical cell to investigate how a steady, controlled flow of electrons can cause 1. Use wire and the dry cell to make one bulb light the bulbs to light up. up. Record your arrangement. 2. Use wire and the dry cell to make two bulbs light Purpose up. Record your arrangement. To discover how to make flashlight bulbs light up 3. If time allows, try other arrangements for step 1 using a standard battery and step 2.

Questions 4. Explain how to use wire and a dry cell to make Materials & Equipment one bulb light up. Include a labelled sketch in • 1 D dry cell your answer.

• 5 insulated copper wires with both ends bare 5. Explain how to use wire and a dry cell to make • two 2.0 V-flashlight bulbs two bulbs light up. Include a labelled sketch in your answer.

CAUTION: Disconnect the wires if they get hot. Do not use dry cells if they show any sign of corrosion.

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During Reading Current Electricity Illustrations The electricity of the electric eel and the electric ray is similar to Support Understanding of the static charges you have felt from a sweater or the huge static Vocabulary charges of lightning. Unfortunately, static charges are not useful As you read the text, be aware for operating electrical devices. They build up and discharge, but of how the photos, diagrams, or they do not flow continuously. other illustrations support your understanding of unfamiliar To operate electrical devices, you need a steady flow of vocabulary. What term or electrons. Unlike static electricity, a flow of electrons moves concept is illustrated by the continuously as long as two conditions are met. First, the flow of photo or diagram? How does the electrons requires an energy source. Second, the electrons will not illustration make the concept flow unless they have a complete path to flow through. This path easier to understand? If you get is called an electrical circuit. The continuous flow of electrons in stuck on unfamiliar terminology, a circuit is called current electricity. check the illustrations as one way to improve your understanding. Electric Circuits A circuit includes an energy source, a conductor, and a load. An electrical load is a device that converts electrical energy to another form of energy. For example, in Figure 11.4, the light bulb is the load. It converts electrical energy to light and heat. WORDS MATTER Many electric circuits also include a switch. A switch is a The word “circuit” comes from a device that turns the circuit on or off by closing or opening the Latin word meaning to go around. The word “circuit” can also be used circuit. When the switch is closed, the circuit is complete and to describe a complete journey of electrons can flow. An open switch means there is a break in the people or objects, such as the circuit of Earth around the Sun. path, so the electrons cannot flow through the circuit. The circuit is turned off when the switch is open.

energy source + electrical load

conducting wires

– switch

Figure 11.4 An electric circuit

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Electrochemical Cells One simple and convenient energy source is a battery. A battery is a combination of electrochemical cells. Each electrochemical cell is a package of chemicals that converts chemical energy into electrical energy that is stored in charged particles. A simple electrochemical cell includes an electrolyte and two electrodes. • An electrolyte is a liquid or paste that conducts electricity because it contains chemicals that form ions. An ion is an atom or a group of atoms that has become electrically charged by losing or gaining electrons. Citric acid is an example of an electrolyte. • Electrodes are metal strips that react with the electrolyte. Two different electrodes, such as zinc and copper, are used in a battery. As a result of the reaction between the electrolyte and electrodes, electrons collect on one of the electrodes, making it negatively charged. The other electrode has lost electrons, so it is positively charged (Figure 11.5).

copper electrode (+) zinc electrode (–)

F

D B Figure 11.5 The citric acid in the grapefruit is the electrolyte. Electrons collect on the zinc C electrode, leaving positive charges on the copper electrode. The meter measures the flow A of electrons.

Wet Cells and Dry Cells E

An electrochemical cell that has a liquid electrolyte is called a wet A – zinc powder and electrolyte, cell. Wet cells are often used as an energy source for cars and where electrons are released other motorized vehicles. An electrochemical cell that uses a paste B – electron collecting rod C – separating fabric instead of a liquid electrolyte is called a dry cell (Figure 11.6). D – manganese dioxide and carbon, You use dry cells in flashlights, hand-held video game devices, where electrons are absorbed cameras, and watches. Each electrode in a dry cell or battery can E – negative terminal, where electrons leave also be called a terminal. Terminals are the end points in a cell or F – positive terminal, where electrons return battery where we make a connection. Figure 11.6 An alkaline dry cell

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Recycling and Recharging Dry Cells Eventually, the chemicals in a dry cell are used up and can no longer separate charges. When you are finished using a dry cell, you should recycle it rather than discard it (Figure 11.7). Dry cells can contain toxic materials, such as the heavy metals nickel, cadmium, and lead. Household dry cells and batteries are responsible for over 50 percent of all the heavy metals found in landfills. Some dry cells are rechargeable cells. Chemical reactions in a rechargeable cell can be reversed by using an external energy source to run electricity back through the cell. The reversed flow of electrons restores the reactants that are used up when the cell produces electricity. Since rechargeable dry cells can be reused many times, they have less impact on

Figure 11.7 During recycling, the chemicals in a dry cell are the environment than non-rechargeable dry separated and can be reused. cells.

Fuel Cells A fuel cell is an electrochemical cell that generates electricity directly from a chemical reaction with a fuel, such as hydrogen (Figure 11.8). The cell is not used up like an ordinary cell would be because as the electricity is produced, more fuel is added. Much of the energy produced by fuel cells is wasted as heat, but their design continues to be refined. Fuel cells are used in electric vehicles and may one day be used in smaller devices such as laptop computers.

Learning Checkpoint

1. How is current electricity different from static electricity? 2. What is an electric circuit? Figure 11.8 A fuel cell converts 3. List three components of an electric circuit. chemical energy into electrical 4. What is the difference between an electrolyte and an electrode? energy. This fuel cell is slightly smaller than this textbook. 5. Why should dry cells be recycled rather than thrown in the trash?

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Potential Difference Each electron has electric potential energy. Potential energy is the energy stored in an object. Picture an apple hanging from a WORDS MATTER low branch on an apple tree (Figure 11.9). The apple has potential The electrochemical cell was first presented to the Royal Society of energy because of its position above the ground. If the apple falls London in 1800 by the Italian down, it will convert its stored energy, or potential energy, into physicist Alessandro Volta. The words “voltage and “volt” are named in his motion. Suppose an apple were on a higher branch. It would have honour. even more potential energy to convert.

Figure 11.9 The greater the height of an apple above the ground, the greater its potential energy.

A battery has chemical potential energy in the electrolyte in its electrochemical cells. The chemicals in the electrolyte react with the electrodes. This causes a difference in the amount of electrons between the two terminals. One terminal in a battery has mainly negative charges (electrons). The other terminal has – – – – + + mainly positive charges (Figure 11.10). The negative charges are – + – – + electrons, which can move. They are attracted to the positive + + + charges at the positive terminal. If a conductor, such as a copper wire, is connected to both terminals, then the electrons flow from the negative terminal to the positive terminal. The difference in electric potential energy between two points in a circuit is called the potential difference or voltage (V). This difference causes current to flow in a closed circuit. The Figure 11.10 An electrochemical higher the potential difference in a circuit, the greater the cell or battery gives electrons potential energy of each electron. electric potential energy.

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Measuring Potential Difference The potential difference between two locations in a circuit is measured with a voltmeter. For example, you could place the connecting wires of the voltmeter across the positive and negative terminals of a battery like the rectangular yellow box shown in Figure 11.11. The voltmeter would then display the potential difference of the battery. The SI unit for measuring potential difference is the volt (V).

How Electrons Transfer Energy in a Circuit When you turn on the light switch on a wall, you close the circuit and immediately the light comes on. How do the electrons get from the switch to the light bulb so fast? It may surprise you to Figure 11.11 The orange device is a learn that electrons do not travel from the switch to the bulb. You voltmeter. It is showing a reading of can picture electrons in a wire as being like water in a hose. If a 1.50 V. The yellow device is a battery. hose connected to a tap already has water in it and you turn the tap on, water comes out of the end of the hose immediately. Electrons in a wire work in a similar way. When an energy source is connected to a circuit, electrons in the conductor “push” or repel other electrons nearby. As soon as one electron starts to move at one end of the wire, it pushes the next one, which pushes the next one and so on. By pushing the first electron, you make the last electron move (Figure 11.12). That is why when you flip the switch, the light goes on instantly even though the electrons themselves have not moved from the switch to the light bulb.

Figure 11.12 Electrons in a wire are like marbles in a tube. If you push a marble at one end of the tube, the energy is transmitted through all the marbles. When electrons in a wire are “pushed” from one end, energy is transmitted all along the electrons in the wire.

Learning Checkpoint

1. What is another name for stored energy? 2. How is an apple falling from a tree like the potential difference in a battery? 3. What does potential difference measure? 4. What is another name for potential difference? 5. When you walk into a dark room and turn the light on, do the electrons travel all the way from the switch to the light? Explain your answer.

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Current Electric current is a measure of the amount of electric charge that passes by a point in an electrical circuit each second. Think of the continuous flow of electric current as being like water flowing in a stream. The water keeps on flowing unless its source dries up. As long as the battery continues to separate charges on its terminals, the electrons continue to flow. Because the current flows in only one direction it is called direct current (DC). The flow of current from batteries is DC, but the current that flows through cords plugged into the wall sockets in your home is called alternating current. Alternating current (AC) flows back and forth at regular intervals called cycles. This is the current that comes from generators and is carried by the big power lines to your home.

Measuring Current WORDS MATTER Current in a circuit is measured using an ammeter, as shown in “Ampere” and “ammeter” are named Figure 11.13. The unit of electric current is the ampere (A). An in honour of André-Marie Ampère (1775–1836), a French physicist who ampere is a measure of the amount of charge moving past a point studied electricity and magnetism. in the circuit every second.

Figure 11.13 These ammeters show a reading of 0.50 A. The meter on the right has amperes on the scale below the black curved line.

Current Electricity and Static Electricity Current electricity is different from static electricity because current electricity is the flow of electrons in a circuit through a conductor. Static electricity is the electric charge that builds up on the surface of an object. Static electricity discharges when it is given a path, but it does not continue to flow.

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Electron Flow and Conventional Current Throughout this unit, we refer to current in terms of electrons flowing from a negative terminal to a positive terminal in a battery. However, when scientists studied electricity several hundred years ago, they did not yet know about electrons. They inferred that when electric current flowed from one object to another, it did so because one object had a greater amount of electricity, so the electricity flowed from the higher or more positive source to the lesser or more negative source. The mathematical equations and conventions developed afterward followed this assumption. This view is called conventional current, and it is a different way of describing the movement of electrons in a circuit (Figure 11.14).

(c) (b)

– + (d) (a)

Figure 11.14 Conventional current describes current as leaving the source from the positive terminal (a) and entering the meter at its positive terminal (b). Then, the current is described as passing through the meter and leaving through the negative terminal (c). It then returns to the negative terminal of the source (d).

When you connect an ammeter or voltmeter to a circuit, you need to think in terms of conventional current rather than electron flow (Figure 11.15). There are two terminals on a meter that you use to connect to a circuit. The negative (–) terminal is often black, and the positive (+) terminal is often red. Always connect the positive terminal of the meter to the positive terminal of the electrical source. Connect the negative terminal of the meter to the negative terminal of the electrical source.

Figure 11.15 When you connect an electrical meter, follow the rule “positive to positive, and negative to negative.” The positive red terminal of the meter is connected to the circuit. The positive red terminal of the battery is also connected to the circuit. The negative black terminals of the meter and the battery are connected directly.

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Resistance Resistance is the degree to which a substance opposes the flow of electric current through it. All substances resist electron flow to some extent. Conductors, such as metals, allow electrons to flow freely through them and have low resistance values. Insulators resist electron flow greatly and have high resistance values. Resistance is measured in ohms (⍀) using an ohmmeter. An ohmmeter is a device for measuring resistance. An ohmmeter is usually part of a multifunctional meter called a multimeter (Figure 11.16). When a substance resists the flow of electrons, it slows down the current and converts the electrical energy into other forms of energy. The more resistance a substance has, the more energy it Figure 11.16 Multimeters can be gains from the electrons that pass through it. The energy gained used to measure potential by the substance is radiated to its surroundings as heat and/or difference, current, or resistance. light energy (Figure 11.17).

WORDS MATTER The symbol for ohm, ⍀, is the Greek Figure 11.17 When electrons pass through a resistor, such as the element on this electric letter omega. heater, their electrical energy is converted to heat and to light.

Resistance in a Circuit The more resistance a component has, the smaller its conductivity. For example, current in a circuit might pass through the filament in a light bulb (Figure 11.18). The filament is a resistor, which is any material that can slow current flow. The filament’s high resistance to the electron’s electrical energy causes it to heat up and produce light.

filament

Figure 11.18 The filament in a light bulb is an example of a resistor.

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Resistors and Potential Difference high potential energy Resistors can be used to control current or potential difference in a circuit. When you work with resistors, you should always be aware that they can heat up and cause burns. Use caution when handling them. In a circuit, electrons have a higher potential difference as they enter a resistor compared to when they leave the resistor because they use up some energy in passing through the resistor. You can picture electrons entering a resistor as being at the high potential energy converted end of a ramp, where they have a lot of potential energy. In this to another form of energy analogy, electrons leaving the resistor are at the bottom end of the

Figure 11.19 An electron entering a ramp, where their potential energy has been converted to another resistor is similar to a ball at the form of energy (Figure 11.19). high end of a ramp, where potential energy is greater. Types of Resistors A wide variety of resistors are made for different applications, especially in electronics (Figure 11.20). For example, televisions contain dozens of different resistors. Resistors can be made with a number of techniques and materials, but the two most common types are wire-wound and carbon-composition. A wire-wound resistor has a wire made of heat-resistant metal wrapped around an insulating core. The longer and thinner the wire, the higher the resistance. Wire-wound resistors are available with values from 0.1 ⍀ up to 200 k⍀. The wire for a 200-k⍀ resistor is very thin. Carbon-composition resistors are made of carbon mixed with other materials. The carbon mixture is moulded into a cylinder with a wire at each end. By varying the size and composition of Figure 11.20 Resistors come in the cylinder, manufacturers produce resistances from 10 ⍀ to many shapes and sizes. The type of ⍀ material the resistor is made from 20 M . Moulded carbon resistors are cheaper to make than wire- affects its resistance. wound resistors but less precise.

Learning Checkpoint

1. What is electric current? 2. What does “resistance” refer to in terms of electron flow? 3. Copy and complete the following table in your notebook. Some answers are provided for you.

Quantity Abbreviation Unit Symbol Suggested Activities • Potential difference D13 Quick Lab on page 444 ampere D14 Quick Lab on page 445 D15 Design a Lab on page 446 ⍀

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Resistance in a Wire Take It Further The flow of water in pipes is another useful model of electricity A number of rechargeable dry (Figure 11.21). Not all pipes transport water equally well. The cells are available, such as NiCd, NiMH, and lithium ion. Research longer and thinner a pipe is, the more resistance it has to the flow the different types of rechargeable of water. A pipe with a bigger diameter has less resistance, which dry cells. Compare their allows a greater flow of water. composition, lifetime, cost, and ability to hold charges. Begin your Similarly, the amount of resistance in a circuit affects the research at ScienceSource. electrical current. For any given potential difference, current decreases if you add resistance. As with water flow, you get the least resistance with a short, wide path with no obstructions. The shorter and thicker the wire, the less resistance it creates for electrons. Other factors affecting the resistance of a wire include the material it is made from and its temperature, as shown in Table 11.1.

Figure 11.21 Resistance in a pipe reduces the flow of water. The smaller the pipe, the greater the resistance, so the flow is less. Resistance in a conductor reduces the flow of electrons.

Table 11.1 Factors Affecting the Resistance of a Wire

Factor How Factor Affects Resistance Material Silver has the least resistance but is very expensive to use in wires. Most conducting wires are made from copper.

Temperature As the temperature of the wire increases, its resistance increases and its conductivity decreases. In other words, a colder wire is less resistant than a warmer wire.

Length Longer wires offer more resistance than shorter wires. If the wire doubles in length, it doubles in resistance.

Cross-sectional area Wider wires offer less resistance than thinner wires. If the wire doubles in width, its resistance is half as great. Conducting wires that carry large currents need large diameters to lessen their resistance.

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D13 Quick Lab Make Your Own Dimmer Switch

Some homes have dimmer switches on their lights. Procedure A dimmer switch allows you to adjust light levels in a room from nearly dark to very bright by moving a 1. Connect the battery to the light bulb, and set up lever or turning a knob. the Nichrome™ wire on the board as shown in Figure 11.22. Make sure the Nichrome™ wire is Purpose connected at one end but not the other, leaving To use resistance to control the amount of current your circuit open. Have your teacher approve flowing through a light bulb your set-up before you proceed further. 2. Close your circuit by connecting the other end of the Nichrome™ wire, maximizing the length of the wire in the circuit. Note the brightness of the Materials & Equipment bulb (Figure 11.22(a)).

• battery 3. Move the alligator clips on the Nichrome™ wire • connecting wires with alligator clips closer together (Figure 11.22(b)). Note the • flashlight bulb (2.5 W) and socket brightness of the bulb. • 40-cm of 32-gauge Nichrome™ wire 4. Continue to observe the brightness of the bulb • piece of wood with screws (see Figure 11.22) as you move one of the alligator clips along the Nichrome™ wire.

Questions 5. (a) How did the brightness of the bulb change as you moved the alligator clips? (b) Explain why the brightness changed as the length of wire changed.

6. How do your observations in this activity help explain how a dimmer switch works?

(a) (b)

Figure 11.22 The brightness of the bulb changes, depending on whether the space between the clips on the wire is (a) larger or (b) smaller.

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D14 Quick Lab Modelling Potential Difference, Current, and Resistance

A model in science can help you picture a process or 6. While the water is running, pinch the end of the object that may be hidden from view or that may be tubing slightly. Observe what happens to the too large or too small to view directly. You can also flow. Empty the bucket (if using) when you have use a scientific model to help you communicate your finished timing. ideas. 7. Record the time it takes to fill the beaker or Purpose bucket using the slightly pinched length of tubing. Empty the container when you have To model interactions among potential difference, finished timing. current, and resistance using water flowing in a hose 8. Record the time it takes to fill the beaker or bucket using an open length of tubing.

9. Record the time it takes to fill the beaker or Materials & Equipment bucket using an open length of tubing and the • 50-cm or longer length • 1000-mL beaker or water turned on full. Empty the container when of rubber tubing bucket you have finished timing.

• water tap and sink or • stopwatch 10. Follow your teacher’s instructions for cleaning bucket up.

Procedure Questions 1. Create a data table with headings like the ones 11. (a) How did the exit times compare for the tubes shown below. Give your data table a title. in step 3 and step 5? 2. Attach one end of the tubing to a tap. Place the (b) How would you explain any difference in other end of the tubing in a bucket or sink as far times? from the tap as the tubing will reach without 12. What part of this activity modelled electric bending. current in a circuit? 3. Turn on the cold water to a medium flow. Record 13. (a) How does the size of the opening in the the time it takes for water to exit the tubing. tubing affect water flow? 4. Pinch the end of the tubing, and then turn off (b) Relate the size of the opening of the tubing to the water. Keep the end pinched. Empty the resistance in wires. bucket (if using) when you have finished timing. 14. (a) How does how far a tap is opened affect 5. Turn on the cold water to a midway point, and water flow through the tubing? release the end of the tubing at the same time. (b) Relate how far a tap is opened to potential Record the time it takes for water to exit the difference in a circuit. tubing into the sink or bucket.

Time to Exit Empty Time to Exit Time to Fill Beaker Time to Fill Beaker Time to Fill Beaker Tube (s) Pinched Tube (s) or Bucket with or Bucket with or Bucket with Pinched Tube (s) Open Tube (s) Water on Full (s)

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SKILLS YOU WILL USE Skills Reference 2  Using equipment, materials, D15 Design a Lab and technology accurately and safely  Adapting or extending Investigating Conductivity procedures

Question 4. Place the metal tips of the conductivity tester in How does the conductivity of different solutions the distilled water (Figure 11.23). Record the compare? conductivity reading of the distilled water in your table. If your conductivity tester is a light bulb, describe the brightness of the bulb.

5. Repeat steps 3 and 4 with 50-mL samples of tap Materials & Equipment water, salt water, vinegar, copper(II) sulphate • 100-mL graduated • vinegar solution, and any other solutions your teacher provides for you to use. After each conductivity cylinder • copper(II) • 250-mL beaker sulphate solution measurement, empty the beaker as directed by your teacher and rinse it with distilled water. • distilled water • other solutions Also, wipe off the tips of the conductivity tester. • conductivity tester provided by your teacher Make sure that you insert the tips to the same • tap water depth in each solution. • salt water 6. Clean up your work area. Make sure to follow your teacher’s directions for safe disposal of materials. Wash your hands thoroughly.

Part 2

7. Plan an investigation to compare the conductivity of other solutions. Have your teacher approve your plan, and then conduct your investigation.

Analyzing and Interpreting

8. How did you determine whether there were differences in conductivity between the solutions you tested? Figure 11.23 Conductivity tester 9. Rank the substances in order of high Procedure conductivity to low conductivity. Part 1 10. How did your results compare with your predictions? 1. Read through the procedure. Then, design a Skill Practice data table to record your predictions and your conductivity readings of the solutions you will 11. Make an hypothesis about why there were test. Give your table a title. differences in conductivity between the 2. Predict which solutions will be the best conductors solutions. and which will be the poorest conductors. Record Forming Conclusions your predictions and the characteristics on which you are basing your predictions. 12. Write a summary of your results that answers the question “How does the conductivity of different 3. Put 50 mL of distilled water into a 250-mL solutions compare?” beaker.

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11.1 CHECK and REFLECT

Key Concept Review 13. Make a list of similarities between the flow of water and an electric circuit. 1. (a) Describe the two main components of an electrochemical cell. 14. A student is planning to test several different electrode combinations to see which would (b) How does a wet cell produce electricity? produce the greatest potential difference in a 2. What direction do electrons flow in a wet cell. State whether each of her choices circuit? will work. Explain why or why not. Her choices for electrodes are as follows: 3. (a) What device measures potential (a) both zinc difference? (b) zinc and copper (b) What are the units for measuring potential difference? (c) both copper

4. (a) What device measures current? 15. The illustration below shows a design for a dry cell. How does this design differ from the (b) What are the units for measuring dry cell shown in Figure 11.6 on page 435? current? insulator positive 5. What is the difference between potential insulated terminal zinc can casing difference and current? (negative electrode) 6. What is the difference between DC electricity and AC electricity?

7. (a) What is the function of an electrical load in a circuit? (b) List four examples of electrical loads. carbon 8. What does resistance refer to in a circuit? electrode negative electrolyte terminal paste 9. What is the role of a resistor in a circuit? insulator

10. What are four factors affecting resistance in Question 15 a wire? Reflection Connect Your Understanding 16. What do you now understand about current 11. Why must a circuit be closed in order for a electricity that you did not know before current to flow? reading this chapter? 12. Use a three-circle Venn diagram to compare and contrast alternating current, direct For more questions, go to ScienceSource. current, and static electricity.

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