Electrical Power and Energy

Electrical Power

• We briefly discussed power (P = W/T), where P = power, W = Work, and T = Time– Power was defined as the rate at which work is

done– Electricity can do work• Examples: Hair dryers, fans, power tools etc.

• Electrical Power is defined as the rate at which electrical energy is converted to another form of energy

Calculating Power• Electrical Power just like power is measured in

Watts• The amount of power used by an appliance is

calculated as:Power = Current x Voltage

orWatts = Amperes x Volts

or P = I x V

Example

• A calculator has a 0.01 A current flowing though it. It operates with a potential difference of 9 V. How much power does it use?– What do we know? P = I x V• P = ? I = 0.01A V = 9V

P = 0.01A x 9VP = 0.09W

Another Example

• A microwave oven uses 1000 W of power. The voltage source is 120 V. What is the current flowing through the microwave?

• P = I x V, however we need to calculate for I• I = P/V• I = 1000W/ 120V• I = 8.3A