<meta http-equiv="refresh" content="1; url=/nojavascript/"> Electric Power and Electrical Energy Use ( Read ) | Physics | CK-12 Foundation
Dismiss
Skip Navigation

Electric Power and Electrical Energy Use

%
Best Score
Practice
Best Score
%
Practice Now
Electric Power and Electrical Energy Use
 0  0  0

Miranda has to use a hair dryer in order to dry her long hair quickly enough to get to school on time. She has a powerful hair dryer that dries her hair faster than a less powerful hair dryer would. That’s because a more powerful hair dryer changes electric current to thermal energy more quickly.

Electric Power

The rate at which a device changes electric current to another form of energy is called electric power . The SI unit for power—including electric power—is the watt. A watt equals 1 joule of energy per second. High wattages are often expressed in kilowatts, where 1 kilowatt equals 1000 watts. The power of an electric device, such as a hair dryer, can be calculated if you know the voltage of the circuit and how much current the device receives. The following equation is used:

Power (watts) = Current (amps) x Voltage (volts)

Assume that Miranda’s hair dryer is the only electric device in a 120-volt circuit that carries 15 amps of current. Then the power of her hair dryer in kilowatts is:

Power = 15 amps x 120 volts = 1800 watts, or 1.8 kilowatts

Q: If a different hair dryer is plugged into a 120-volt circuit that carries 10 amps of current. What is the power of the other hair dryer?

A:  

Electrical Energy Use

Did you ever wonder how much electrical energy it takes to use an appliance such as a hair dryer? Electrical energy use depends on the power of the appliance and how long it is used. It can be calculated with this equation:

Electrical Energy = Power x Time

If Miranda uses her 1.8-kilowatt hair dryer for 0.2 hours, how much electrical energy does she use?

Electrical Energy = 1.8 kilowatts x 0.2 hours = 0.36 kilowatt-hours

Electrical energy use is typically expressed in kilowatt-hours, as in this example. How much energy is this? One kilowatt-hour equals 3.6 million joules of energy.

Q: Suppose Miranda were to use a 1.2-kilowatt hair dryer for 0.2 hours. How much electrical energy would she use then?

A:  

Summary

  • Electric power is the rate at which a device changes electric current to another form of energy. The SI unit of power is the watt. Electric power can be calculated as current times voltage.
  • Electrical energy use equals the power of the appliance multiplied by the amount of time the appliance is used.

Vocabulary

  • electric power : Rate at which a device changes electric current to another form of energy.

Review

  1. Define electric power. What is the SI unit for power?
  2. A microwave is the only electric device in a 120-volt circuit. If the circuit has 7.5 amps of current, what is the electric power of the microwave?
  3. Calculate the electrical energy use of the microwave in question 2 if it used for 0.05 hours.

Image Attributions

Reviews

Email Verified
Well done! You've successfully verified the email address .
OK
Please wait...
Please wait...

Original text