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Home Minds On Electric Circuits Mission EC3 Voltage, Power and Energy Help Help 3

Mission EC3 Voltage, Power and Energy

The Question

Two identical light bulbs are turned on in a house. If one is left on for twice the time, it will ____ as the other.

Formula Fix

Mathematically, power is a rate quantity - a time-based quantity. It is the rate at which work is done by a battery upon a charge. Power is also the rate at which energy is used up by an appliance. 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 = ∆E / t.

Think About It

Appliances that are onin a home use up electrical energy. Another way to put it is that they transform the electrical energy into other forms of energy such as light energy, thermal energy, and mechanical energy. The rate at which the energy is used up is known as the power. A light bulb is rated in terms of the rate at which it uses energy when plugged into a 110-120 volt U.S. outlet. A 60-Watt bulb will use 60 Joules of electrical energy per second. Leaving the bulb on for two hours will not change the wattageof the bulb. It will remain a 60-Watt bulb for its entire lifetime. A rearrangement of the equation in the Formula Frenzy section would yield the relationship
∆E = P • t.

As can be seen in this equation, a doubling of the time that a light bulb is on will double the amount of energy used by the bulb.

Bright Idea

Current electricity language can be confusing. Confusing or not, it is the language that will be used to describe and explain the physics of electric circuits. Many of the incorrect responses to this question represent a statement that reflects a lack of understanding of terms. You may find it useful (particularly if you have missed this question frequently) to develop a list of terms with their definition, equation, units and a short and meaningful description. The following terms should be included on the list: current, potential difference (voltage), potential energy (work), electric power, charge, current and resistance.

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