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Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Objectives Describe how batteries are sources.

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Presentation on theme: "Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Objectives Describe how batteries are sources."— Presentation transcript:

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2 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Objectives Describe how batteries are sources of voltage. Explain how a potential difference produces a current in a conductor. Define resistance. Calculate the resistance, current, or voltage, given the other two quantities. Distinguish between conductors, superconductors, semiconductors, and insulators. Chapter 16

3 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer 1.Dry cell batteries are a source of mobile electrical power. Name five devices that use dry cell batteries. 2.Give reasons why copper is normally used to wire a home for electricity. 3.Why is it important to unplug a device by pulling the plug instead of by yanking it out of the socket by pulling on the electrical cord? 4.Why are electrical appliances, such as razors, hair dryers, and curling irons, not to be used in the bathtub or shower? Section 2 Current Chapter 16

4 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Voltage and Current Electrical potential energy is the ability to move an electric charge from one point to another. The electrical potential energy of the moving charge decreases because the electric field does work on the charge. The electrical potential energy depends on the distance between two charged objects for both an attractive and a repulsive electric force. Chapter 16

5 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrical Potential Energy Section 2 Current The electrical potential energy between two negative charges decreases as the distance between them increases. Chapter 16

6 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrical Potential Energy and Relative Position Section 2 Current The electrical potential energy of a charge depends on its position in an electric field. Chapter 16

7 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electrical Potential Energy Section 2 Current Chapter 16

8 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Voltage and Current, continued Potential difference is measured in volts. The potential difference between any two points, is the work that must be done against electric forces to move a unit charge from one point to the other. The volt, V, is equivalent to one joule per coulomb (1 J/C). Potential difference is often called voltage. Section 2 Current Chapter 16

9 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Potential Difference Section 2 Current Chapter 16

10 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Voltage Section 2 Current Chapter 16

11 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Voltage and Current, continued There is a voltage across the terminals of a battery. A cell is a device that is a source of electric current because of a potential difference, or voltage, between the terminals. One terminal is positive, and the other is negative. Batteries convert chemical energy into electrical energy. Chapter 16

12 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Battery Section 2 Current Chapter 16

13 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electric Cell Section 2 Current Chapter 16

14 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Voltage and Current, continued A voltage sets charges in motion. Current is the rate that electric charges move through a conductor. The SI unit of current is the ampere, A. 1 amp = 1 C/s A battery is a direct current source because the charges always move from one terminal to the other in the same direction. Conventional current is defined as movement of positive charge. The direction of current in a wire is opposite the direction that electrons move in that wire. Chapter 16

15 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Comparing Direct and Alternating Current Section 2 Current Chapter 16

16 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Conventional Current Section 2 Current Chapter 16

17 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Electrical Resistance Resistance is the opposition posed by a material or a device to the flow of current. Resistance is caused by internal friction, which slows the movement of charges through a conducting material. Resistance can be calculated from current and voltage. Chapter 16 The SI unit of resistance is the ohm, Ω. 1 Ω = 1 V/A A resistor is a special type of conductor used to control current.

18 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Math Skills Resistance The headlights of a typical car are powered by a 12 V battery. What is the resistance of the headlights if they draw 3.0 A of current when turned on? 1.List the given and unknown values. Given: current, I = 3.0 A voltage, V = 12 V Unknown: resistance, R = ? Ω Chapter 16

19 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Math Skills, continued 2.Write the equation for resistance. R = 4.0  Chapter 16 3.Insert the known values into the equation, and solve.

20 Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Current Electrical Resistance, continued Conductors have low resistances. Some materials become superconductors below a certain temperature. Certain metals and compounds have zero resistance when their temperature falls below a certain temperature called the critical temperature. Semiconductors are intermediate to conductors and insulators. The controlled addition of specific atoms of other materials as impurities dramatically increases a semiconductor’s ability to conduct electric charge. Chapter 16

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