Recall that power is the rate of doing work. The rate at which electrical energy is converted to another form of energy is electric power. The unit of electric power is the joule per second, or watt (W). Power often is measured in thousands of watts, or kilowatts (kW). Electric power can be calculated by multiplying voltage by current.
Every time you use a 1875-watt hair dryer or turn on a 75-watt light bulb you use electric power. Appliances vary in the amount of power they use.
Calculating Electric Power
An electric oven is connected to a 240-volt line, and it uses 34 amps of current. What is the power used by the oven?
Read and Understand
What information are you given?
Current = I = 34 amps
Voltage = V = 240 volts
Plan and Solve
What unknown are you trying to calculate?
What formula contains the given quantities and the unknown?
Replace each variable with its known value.
= 8200 watts
Look Back and Check
Is your answer reasonable?
The answer is reasonable because an electric oven should use much more power than a 1875-watt hair dryer.
A clothes dryer uses about 27 amps of current from a 240-volt line. How much power does it use?
A camcorder has a power rating of 2.3 watts. If the output voltage from its battery is 7.2 volts, what current does it use?
A power tool uses about 12 amps of current and has a power rating of 1440 watts. What voltage does the tool require?