1. Chapter 17 Electrical Energy and Current
17 – 4 Electric Power

2. Sources and Types of Currents
Both batteries and generators maintain a potential difference across terminals by converting other forms into electrical energy
In all batteries they convert chemical energy into electrical energy
Generators convert mechanical energy into electrical energy.

3. Types of current
There are two types of currents: direct current (dc) and alternating current (ac).
In direct current, charges move in only one direction.
Due to frequent collisions, the motion is partially random, but with a gradual net movement in one direction.

4. Alternating current
In altering current, the charges continuously oscillate back and forth.
There is no net movement of the electrons in the wire.

5. Electric Power
Electric power is the rate at which charge carriers do work.
P = I ΔV
Remember SI unit of power is the Watt (J/s)

6. Sample Problem
A computer is connected across a 110 V power supply. The computer dissipates 130 W of power in the form of EM radiation and heat. Calculate the resistance of the computer.

7. V = 110 V, P = 130 W, R =?
P = IV
I = P/V = 130W/110 V =
V = I R
R = V/I = 110 V/ =

8. Relating kilowatt∙hours to joules

9. Converting from kilowatt∙hours to Joules

10. Sample Problem
How much would it cost to run the computer in the previous problem for 5 hours. Assume the electric company charges $0.95/kW∙h.