Power Calculations

An alarm clock draws 0.5 A of current when connected to a 120 volt circuit. What amount of power is used by the alarm clock?

A subwoofer needs a household voltage of 110 V to push a current of 5.5 A through its coil. What is the power used by the subwoofer?

If a toaster produces 12 watts of power in a 120-volt circuit, what is the amount of current in the circuit?

An electric heater works by passing a current of 50 A though a coiled metal wire, making it red hot, and uses 120 W of power. What voltage must be applied to run the heater?

Which of these is a measurement of power?

• 100 joules

• 100 watts

• 100 meters per second

• 100 hertz

You do 90 joules of work in 30 seconds. How much power have you generated?

• 30 watts

• 3 watts

• 120 watts

• 270 watts

Answer explanation

Power is calculated as work done divided by time. Here, power = 90 joules / 30 seconds = 3 watts. Therefore, the correct answer is 3 watts.

Electrical power can be calculated using

• Resistance x Voltage

• Voltage x Current 

• Voltage ÷ Current

A car engine does 5000 J of work in 5 seconds. Calculate the power output of the engine.

• 1000 W

• 500 W

• 2500 W

• 2000 W

Tags

DOK Level 2: Skill/Concept

A motor does 1500 J of work in 3 seconds. What is the power of the motor?

• 500 W

• 4500 W

• 150 W

• 300 W

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DOK Level 2: Skill/Concept

Which of the following is a unit of power?

• Joule

• Watt

• Newton

• Pascal

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DOK Level 1: Recall