Electric Power

Answer Me!!!

How is the brightness of a light bulb measured? What do you think is the significance of this?

Electric Power

Power is the rate at which work is done or energy is expended.

Electrical Power is the rate at which electrical energy is expended.

Electrical Power

Electric power is the product of electric current and potential difference

P = V·I Power is still measured in Watts:

watt1second

Joule11ampere1volt

second

Coulomb1

Coulomb

Joule11ampere1volt

Electrical Power and Ohm’s Law

R

VRIVIP

22

Electrical Energy

Since work is define by:

Electrical energy is measured in Joules. Energy is a scalar quantity.

R

tVRtIVItW

PtW2

2

Practice Problem 1

A microwave oven operating at 120 V is used to heat a hot dog. If the oven draws 12.5 A of current for 45 seconds, what is the power dissipated by the oven?

Practice Problem 2

If the potential drop across an operating 300 W floodlight is 120 V, what is the current through the floodlight?

Practice Problem 3

A potential drop of 50 V is measured across a 250 ohm resistor. What is the power developed in the resistor?

Practice Problem 4

As the potential difference across a given resistor is increased, the power expended in moving the charge through the resistor will _____________.

Practice Problem 5

A toaster dissipates 1500 W of power in 90 seconds. What is the amount of electric energy used by the toaster?

Practice Problem 6

An electric iron operating at 120 V draws 10 A of current. How much heat energy is delivered by the iron in 30 seconds?

Practice Problem 7

An electric dryer consumes 6.0 x 106 J of energy when operating at 220 V for 30 minutes. During operation, the dryer draws how much current?

Practice Problem 8

An operating electric heater draws a current of 10 A and has a resistance of 12 ohms. How much energy does the heater use in 60 seconds?