An amplifier produces an output of 12V rms. In a test it's connected to an 8ohm resistor.?

Question

What is the rms power and the peak power dissipated in the resistor?

Answer 1

rms power should just be E^2/R = 144/8 = 18 watts

But peak voltage is sqrt(2) x RMS. And squaring that gives you 2 x RMS^2, or simply 2 x the RMS power = 36 watts

That's why you see that advertisers of amplifiers often use peak power. They can double the apparent power output just by including the word "peak".

Answer 2

There is truly no "Peak" power.

As others have pointed out it is a mechanism of the audio electronics industry to inflate the statistics of their amplifiers and speakers. In other words, its just a number.

Power is the ability to do work, or to "create smoke" as my electronics Prof used to say. That is calculated using rms figures only.

The calculation is actually p=V^2/R * cos (phase angle) with the phase angle defined as the amount that the current and voltage are out of phase. in a purely resistive circuit the phase angle is 0 and cos(0) is 1, so its not considered.

However, a speaker is an impedance meaning there are reactive elements (largely inductive, but with some resistance and parasitic capacitance) which will put current out of phase. So depending on that phase angle So you may not get exactly 18W

Answer 3

I hate to be picky but 12*sqrt(2) is 16.968 which plugged into
E^2/8 = 35.99 or as near 36 as makes no difference, not 38 i.e. Peak power is twice RMS power.

Answer 4

P = E^2/R
P = 12^2/8
P = 18 Watts

Peak voltage (based on a pure sine wave) is 1.414 * Vrms = 17 volts

17^2 / 8 = 38 Watts peak

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Answer 5

18 w of power