(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

The power supply for a stereo amp develops an output of 22 volts at 2.8 amps. If the overall efficiency of the power supply is 78%, what is the input current that it will draw from a 117 volt source.

2. Relevant equations

P = EI

3. The attempt at a solution

Eo = 22 V

Io = 2.8 Amps

Po = 22 * 2.8 = 61.6 watts

Pi = 61.6 / .78 (efficiency) = 79.0 watts

Ei = 117 V

Ii = 117 / 79.0 = 1.48 amps

Basically is this right?

I thought what you put in always has to be bigger then what you get out?

if so then how can 1.48 amps in = 2.8 amps out?

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# Homework Help: Effocoency Question

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