1. Power
January 12, 2016

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

3. 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.

4. 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: P= I x V
Remember P= Power I= Current V=Voltage

5. When a hair dryer is plugged into a 0. 12 kV outlet, it has a 9
When a hair dryer is plugged into a kV 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

6. A color TV has a power rating of 320 W
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

7. 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 500 cA. 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

8. 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!

9. Now Finish Up Your Circuits Lab
If lab is finished complete parts 4&5 in your homework packet.
Test will be Wednesday- January 20th
Next lab will be this Thursday