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Mission EC3 Voltage, Power and Energy

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Hold down the T key for 3 seconds to activate the audio accessibility mode, at which point you can click the K key to pause and resume audio. Useful for the Check Your Understanding and See Answers.

The Question

When you pay your electric bill, you pay for the number of kilowatt x hours of electricity that you use. You are paying for the ___ you use.

Formula Fix

Mathematically, power is a rate quantity - a time-based quantity. It is the rate at which a force does work upon a charge. Power (P) is calculated from knowledge of the work done (W) and the time (t) required to do this work. The formula is

P = W / t.

Think About It

The unit kilowatt•hour is a unit of power multiplied by a unit of time. The equation in the Formula Frenzy section relates power, work and time. This equation can be rearranged to the form W = P•t. Once done, it is clear that a unit of power multiplied by a unit of time would be a unit of work. So kilowatt x hour is a unit of work or energy. This makes sense because your electric bill gives an indication of the quantity of electrical energy that a household consumes each month.

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