I’m trying to calculate the average power dissipated as the heat in the resistor.

A 12 V amplitude sinusoidal signal is applied across a 500 ohm resistor.

I have determined the current amplitude to be 0.024 A and the root mean square to be 16.97 mA.

I use P = I x V = 0.024 x 12 = 0.288 W

Where P is the power, I is the current and V is the voltage.

Is this correct ?

  • \$\begingroup\$ No. You need to multiply RMS values of both current and voltage. \$\endgroup\$ – Eugene Sh. Dec 21 '18 at 18:12
  • \$\begingroup\$ So it should be 0.144 W ? \$\endgroup\$ – Dan Khan Dec 21 '18 at 18:13
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    \$\begingroup\$ "12V amplitude" - is that 12Vrms, peak, or peak-peak? \$\endgroup\$ – Reinderien Dec 21 '18 at 18:27
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    \$\begingroup\$ @Reinderien - or average (mean )? \$\endgroup\$ – WhatRoughBeast Dec 21 '18 at 18:41
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    \$\begingroup\$ @WhatRoughBeast unlikely. Since there is no mention of a DC rail, the mean would be 0. \$\endgroup\$ – Reinderien Dec 21 '18 at 18:44

With AC the real power is

(From: https://en.wikipedia.org/wiki/Electric_power#Alternating_current)

Cosθ is 1 because you have resisitive load.

Thus you have to calculate with RMS values.

Note that power can also be calculated as

(From: https://en.wikipedia.org/wiki/Electric_power#Resistive_circuits)

and RMS voltage is

RMS voltage

(From: https://en.wikipedia.org/wiki/Root_mean_square)

Thus your power is enter image description here


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