Transcript File

Power
January 12, 2016
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: P= I x V
◦ Remember P= Power
I= Current
V=Voltage
When a hair dryer is plugged into a
0.12 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

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 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

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!
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
