Goals To calculate resistance using Ohms Law To
- Slides: 8
Goals • To calculate resistance using Ohm’s Law • To define electrical power and short circuit • To calculate electrical power
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.
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:
When a hair dryer is plugged into a 0. 12 k. 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
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
The current in the heating element of an electric iron is 500 c. 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
UNITS Reminder • You CANNOT use any prefixes in these calculations. (Just like Ohm’s Law) • For example: – 0. 15 k. W must be converted to W before using as power in calculations! – 56 c. A must be converted to A before using as current in calculations – 100 m. V must be converted to V before using as voltage in calculations!
Homework • Parts 4 & 5 of packet (due tomorrow)