1. May 6, 2009
In our lab yesterday, what device did we use to measure the current? Voltage?
What causes circuits to become overloaded?

2. Goals To calculate resistance using Ohm’s Law
To define electrical power and short circuit
To calculate electrical power

3. Lab Work Time (15 min) Questions? You have 15 min to work
Anything not finished after that is HOMEWORK!

4. Q: What is electrical power?
Rate at which electrical work is done
Also called power rating.
Energy associated with electrical charges, whether moving or at rest.

5. Q: What is electrical power?
Symbol for electrical power in an equation is P.
Unit: Watt (W)
Calculated by multiplying the total current (I) through a circuit by the total voltage (V) across a circuit.
Equation:

6. Equation: P = IV Givens: Work: P = (9.1 A)(120 V) Ans: P = 1092 W
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?
Equation: P = IV
Givens:
I = 9.1 A, V = 120 V, P = ? W
Work: P = (9.1 A)(120 V)
Ans: P = 1092 W

7. Equation: I = P/V Givens: Work: I = 320 W/120 V Ans: I = 2.67 A
A color TV has a power rating of 320 W. How much current is in the TV when it is connected to a 120 V power outlet?
Equation: I = P/V
Givens:
P = 320 W, V = 120 V, I = ? A
Work: I = 320 W/120 V
Ans: I = 2.67 A

8. Equation: V = P/I Givens: Work: V = 590 W/ 5.0 A Ans: V = 118 V
The current in the heating element of an electric iron is 5.0 A. If the iron dissipates 590 W of power, what is the voltage across it?
Equation: V = P/I
Givens:
P = 590 W, I = 5.0 A, V =? V
Work: V = 590 W/ 5.0 A
Ans: V = 118 V

9. UNITS Reminder
You CANNOT use any prefixes in these calculations. (Just like Ohm’s Law)
For example:
0.15 kW must be converted to W before using as power in calculations!
56 cA must be converted to A before using as current in calculations
100 mV must be converted to V before using as voltage in calculations!