1. Vocabulary Ch. 13 static electricity law of conservation of charges
conductor
insulator
charging by contact
charging by induction

2. Vocabulary Ch. 13 electric current voltage difference
circuit parallel circuit
resistance electrical power
Ohm’s law
series circuit

3. Chapter 13
Electricity

4. I. Electric Charge
A. Review Vocabulary: Atom → the smallest particle of an element.
B. What does it mean to be electrically neutral? An atom contains equal numbers of protons and electrons, the positive and negative charges cancel out and the atom has no net electric charge.
C. Static Electricity → the accumulation of excess electric charge on an object.

5. D. Law of Conservation of Charge → states that charge can be transferred from one object to another but cannot be created or destroyed. E. How does an object become charged? Electric charges move from one place to another. F. Charges exert forces on each other: Unlike charges (repel, attract) each other; like charges (repel, attract) each other.

7. G. The force between electric charges also depends on the distance between charges. H. Surrounding every electric charge is an electric field that exerts forces on other electric charges. I. Conductor → a material in which electrons can move easily. J. The best electrical conductors are metals. Why? The atoms in metals have electrons that are able to move easily through the material.

8. K. Insulator → a material in which electrons are not able to move easily. L. What are some good insulators? Plastics, wood, rubber, and glass. M. Charging by Contact → the process of transferring charge between objects by touching or rubbing. N. Charging by Induction → the process of rearranging electrons on a neutral object by bringing a charged object close to it.

9. O. What is lightning? A large static discharge; a transfer of charge between clouds and the ground because of a buildup of static electricity. P. What is thunder? The heat from a lightning bolt causes the air molecules to expand very rapidly, producing sound waves we hear as thunder.

11. Q. Grounding 1. A discharge can occur any time that charge builds up in one area. 2. Providing a path for charge to reach Earth prevents any charge from building up. 3. Earth is a large, neutral object that is also a conductor of charge. 4. Grounding → connecting an object to Earth with a conductor to transfer any excess electric charge.

12. 5. What is the purpose of a lightning rod
5. What is the purpose of a lightning rod? To provide a conducting path from the highest point of a building to the ground.
What else may act as a path to ground? Plumbing fixtures, such as metal faucets, sinks, and pipes,…

13. R. What instrument can we use to detect the presence of electrical charge? electroscope

14. II. Electric Current → the net movement of electric charges in a single direction. A. Electric current is measured in amperes (A). B. One ampere is equal to 6,250 million billion electrons flowing past a point every second. C. Voltage Difference → is related to the force that causes electric charges to flow. D. Voltage difference is measured in volts (V).

15. E. Circuit → a closed conducting loop through which an electric current can flow.
F. Batteries 1. Dry-Cell Batteries → consists of two electrodes surrounded by a material called an electrolyte; called a dry cell because the electrolyte is a moist paste, not a liquid solution.

16. Wet-Cell Batteries → contains two connected plates made of different metals or metallic compounds in a conducting solution; contains several wet-cells connected together.
3. Lead-Acid Batteries → contains a series of six wet cells made up of lead and lead dioxide plates in a sulfuric acid solution; most car batteries are lead-acid batteries.

18. G. Resistance → the tendency for a material to oppose electron flow and change electrical energy into thermal energy and light. H. Electrical (conductors, insulators) have much less resistance than (conductors, insulators). I. Resistance is measured in ohms (Ω). J. The electric resistance of most materials usually (increases, decreases) as the temperature of the material increases.

19. K. The resistance of a wire, or any conductor, (increases, decreases) as the wire becomes longer. L. The resistance (increases, decreases) as the wire becomes thinner. M. A simple circuit contains: 1. A source of voltage difference. (Such as a battery) 2. A device that has resistance. (Such as a lightbulb)

20. 3. Conductors that connect the device to the battery terminals.

21. N. Ohm’s Law → states that the current in a circuit equals the voltage difference divided by the resistance.
Ohm’s law can be written as an equation:
I = V/R
P. Where:
I = current measured in amperes.
V = voltage difference measured in volts.
R = resistance measured in ohms.

22. Q. Example: Calculate the voltage difference in a circuit with a resistance of 25 Ω if the current is 0.5 A. 1. I = V/R V = IR 2. V = (0.5 A)(25 Ω) 3. V = 12.5 volts

23. R. Example: A current of 0.5 A flows in a 60 Watt lightbulb when the voltage difference between the ends of the filament is 120 V. What is the resistance of the filament? 1. I = V/R R = V/I 2. R = 120 V/0.5 A 3. R = 240 Ω

24. III. Electrical Energy A
III. Electrical Energy A. Series Circuit → a circuit in which electric current has only one path to follow.
B. When any part of a series circuit is disconnected, no current flows through the circuit, this is called an open circuit.

25. C. Parallel Circuits → a circuit in which electric current has more than one path to follow.
D. What are the advantages to parallel circuits? When one branch of the circuit is opened, current continues to flow through the other branches.

27. E. What is the purpose of an electrical fuse. How does it work
E. What is the purpose of an electrical fuse? How does it work? To prevent electric circuits from over heating. A small piece of metal melts if the current becomes too high; when it melts it causes a break in the circuit, stopping the flow of current.

28. F. What is the purpose of a circuit breaker. How does it work
F. What is the purpose of a circuit breaker? How does it work? It prevents a circuit from overheating and causing a fire. A circuit breaker contains a piece of metal that bends when the current is so large that it gets hot. The bending causes a switch to flip and open the circuit.

29. G. Why is electricity so useful
G. Why is electricity so useful? Electricity can easily be converted into other types of energy. H. Electrical Power  the rate at which electrical energy is converted to another form of energy.

30. I. Electrical power can be calculated by the following equation: P = IV J. Where: P = electrical power measured in watts. I = current measured in amperes. V = voltage difference measured in volts.

31. K. Example: A toaster oven is plugged into an outlet that provides a voltage difference of 120 V. What power does the oven use if the current is 10 A? 1. P = IV 2. P = (10 A)(120 V) 3. P = 1200 Watts

32. L. A VCR that is not playing still uses 10. 0 W of power
L. A VCR that is not playing still uses 10.0 W of power. What is the current if the VCR is plugged into a 120 V electrical outlet? 1. P = IV I = P/V 2. I = 10.0 W/120 V 3. I = 0.83 Amperes

33. M. Electric companies charge by the amount of electrical energy used. N. Electrical energy is usually measured in units of kilowatt-hours (kWh).

34. O. Electrical energy can be expressed as an equation: E = Pt P
O. Electrical energy can be expressed as an equation: E = Pt P. Where: E = electrical energy measured in kWh. P = electrical power measured in kW. t = time measured in hours.

35. Q. Example: A refrigerator operates on average for 10. 0 hours a day
Q. Example: A refrigerator operates on average for 10.0 hours a day. If the power rating of the refrigerator is 700 W, how much electrical energy does the refrigerator use in one day? 1. E = Pt 2. E = (0.7 kW)(10.0 h) 3. E = 7 kWh

36. Additional Questions for Chapter 13 Test p. 884, #’s 140, 141, 146, 147