# electric power and electrical energy use

## 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 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 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: She would use: Electrical Energy = 1.2 kilowatts 0.2 hour = 0.24 kilowatt-hours

## electric power

The rate at which a device changes electric current to another form of energy is called electric power. The SI unit for powerincluding electric poweris 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) Voltage (volts) Assume that Mirandas 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 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: Substitute these values in the power equation: Power = 10 amps 120 volts = 1200 watts, or 1.2 kilowatts

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

electric power is the rate at which an electric device changes electrical energy to another form of energy.

``````-->  a. true

b. false
``````

which equation can be used to calculate the power of an electric device?

``````-->  a) power = current x voltage

b) power = current/voltage

c) power = voltage/current

d) none of the above
``````

a watt equals one

``````a) volt per second.

b) amp per second.

c) ohm per second.

-->  d) joule per second.
``````

one kilowatt equals 100 watts.

``````a. true

-->  b. false
``````

if an electric device in a 120-volt circuit uses 10 amps of current, then the power of the device is

``````-->  a) 1200 watts.

b) 130 watts.

c) 110 watts.

d) 12 watts.
``````

which equation can be used to calculate the electrical energy used by an appliance?

``````a) energy = power/time

-->  b) energy = power x time

c) energy = time/power

d) energy = power + time
``````

## diagram questions

No diagram questions associated with this lesson