MCAT Physics Question 80: Answer and Explanation

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Question: 80

5. A transformer is a device that takes an input voltage and produces an output voltage that can be either larger or smaller than the input voltage, depending on the transformer design. Although the voltage is changed by the transformer, energy is not, so the input power equals the output power. A particular transformer produces an output voltage that is 300 percent of the input voltage. What is the ratio of the output current to the input current?

A. 1:03
B. 3:01
C. 0.25
D. 300:01:00

Correct Answer: A

Explanation:

We are told that transformers conserve energy so that the output power equals the input power. Thus P_out = P_in, or I_outV_out = I_inV_in. There is therefore an inverse proportionality between current and voltage. If the output voltage is 300% of the input voltage (3 times its amount), then the output current must be

of the input voltage. This can be represented as a 1:3 ratio.

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