1. Electric Power and Electrical Energy
Chapter 16
Section 3 Circuits
Electric Power and Electrical Energy
Electrical energy is the energy that is associated with charged particles because of their positions.
Electric power is the rate at which electrical energy is used in a circuit.
The rate at which electrical work is done is called electric power.
The SI unit for power is the watt (W).
1 W = 1 A  1 V

2. Electric Power and Electrical Energy, continued
Chapter 16
Section 3 Circuits
Electric Power and Electrical Energy, continued
If you combine the electric power equation above with the equation V = IR, the power lost, or dissipated, by a resistor can be calculated.
Electric companies measure energy consumed in kilowatt-hours.
1 kW•h = 3.6  106 J.

3. Equation for Electric Power
Chapter 16
Section 3 Circuits
Equation for Electric Power

4. Chapter 16
Section 3 Circuits
Math Skills
Electric Power When a hair dryer is plugged into a 120 V outlet, it has a 9.1 A current in it. What is the hair dryer’s power rating?
1. List the given and unknown values.
Given: voltage, V = 120 V
current, I = 9.1 A
Unknown: electric power, P = ? W

5. Chapter 16 Math Skills, continued
Section 3 Circuits
Math Skills, continued
2. Write the equation for electric power.
power = current × voltage
P = IV
3. Insert the known values into the equation, and solve.
P = (9.1 A)(120 V)
P = 1.1 × 103 W

6. Fuses and Circuit Breakers
Chapter 16
Section 3 Circuits
Fuses and Circuit Breakers
When electrical wires carry more than a safe level of current, the circuit is said to be overloaded.
A short circuit can happen if a wire’s insulation wears down, two wires may touch, creating an alternative pathway for current.
Fuses melt to prevent circuit overloads.
A fuse an electrical device that contains a metal strip that melts when current in the circuit becomes too great.

7. Fuses and Circuit Breakers
Chapter 16
Section 3 Circuits
Fuses and Circuit Breakers
Circuit breakers open circuits with high current.
A circuit breaker a switch that opens a circuit automatically when the current exceeds a certain value.
The circuit breaker acts as a switch.
Unlike fuses, circuit breakers can be reset by turning the switch back on.

8. Chapter 16
Section 3 Circuits
Fuse

9. Chapter 16
Section 3 Circuits
Concept Mapping

10. Understanding Concepts
Chapter 16
Standardized Test Prep
Understanding Concepts
1. A 12-volt battery is connected to a light bulb that has a resistance of 240 ohms. Calculate the amount of current in amperes drawn by the circuit.
A A
B. 0.5 A
C. 2.0 A
D A

11. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
1. A 12-volt battery is connected to a light bulb that has a resistance of 240 ohms. Calculate the amount of current in amperes drawn by the circuit.
A A
B. 0.5 A
C. 2.0 A
D A

12. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
2. Which of the following statements is true?
F. Electrical forces exist between any two neutral particles.
G. Electrical forces exist between any two charged particles.
H. Electrical forces exist only between particles with the same charge.
I. Electrical forces exist only between particles with opposite charges.

13. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
2. Which of the following statements is true?
F. Electrical forces exist between any two neutral particles.
G. Electrical forces exist between any two charged particles.
H. Electrical forces exist only between particles with the same charge.
I. Electrical forces exist only between particles with opposite charges.

14. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
3. What happens to an object that is charged by induction?
A. It acquires excess electrons.
B. It remains electrically neutral.
C. It acquires a net charge from the object that is inducing the charge.
D. A current exists between it and the object that is inducing the charge.

15. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
3. What happens to an object that is charged by induction?
A. It acquires excess electrons.
B. It remains electrically neutral.
C. It acquires a net charge from the object that is inducing the charge.
D. A current exists between it and the object that is inducing the charge.

16. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
4. A stream of water is deflected when a negatively charged rod is held close to it. Use the concept of induced charge to explain what happens.

17. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
4. A stream of water is deflected when a negatively charged rod is held close to it. Use the concept of induced charge to explain what happens.
Answer: A charge is induced on the water by the charged rod. Attraction between the charged part of the stream and the rod deflects the flow.

18. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
5. How does a fuse protect a circuit from overloading?

19. Understanding Concepts, continued
Chapter 16
Standardized Test Prep
Understanding Concepts, continued
5. How does a fuse protect a circuit from overloading?
Answer: The fuse has a thin wire with a low melting point. When electrical resistance increases the temperature too high, it melts and breaks the circuit.

20. Chapter 16 Reading Skills
Standardized Test Prep
Reading Skills
In 1909 Robert Millikan measured the charge on an electron in what is known as the oil-drop experiment. He sprayed oil droplets into a chamber. Two plates with opposite charges produced an electric field. Some of the drops acquired a negative charge. The field was adjusted so there was an upward force equal to the downward pull of gravity. From the strength of this force, Millikan could calculate the amount of the electric charge on the drop.
6. Analyze how the electric field could cause an oil drop to float inside the chamber.

21. Reading Skills, continued
Chapter 16
Standardized Test Prep
Reading Skills, continued
6. Analyze how the electric field could cause an oil drop to float inside the chamber.
Answer: Electrical forces between the charged particle an the charged plates balance the downward pull of gravity.

22. Interpreting Graphics
Chapter 16
Standardized Test Prep
Interpreting Graphics
7. Which metal would be the best choice for a power line, based on electrical resistance?
F. aluminum
G. iron
H. lead
I. silver

23. Interpreting Graphics
Chapter 16
Standardized Test Prep
Interpreting Graphics
7. Which metal would be the best choice for a power line, based on electrical resistance?
F. aluminum
G. iron
H. lead
I. silver

24. Interpreting Graphics
Chapter 16
Standardized Test Prep
Interpreting Graphics
8. Which metal would most likely be then best substitute for the tungsten filament in an incandescent light bulb based on resistance?
A. aluminum
B. iron
C. lead
D. silver

25. Interpreting Graphics
Chapter 16
Standardized Test Prep
Interpreting Graphics
8. Which metal would most likely be then best substitute for the tungsten filament in an incandescent light bulb based on resistance?
A. aluminum
B. iron
C. lead
D. silver