Power of an ac source

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iVenki

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Here is the sentence that I read in the book.

For a generator of emf E volts (rms) and internal resistance R, the available power is E^2/4R.

But I thought the power of an ac source =E^2/R.

How did you get that 4 in the denominator?

Thanks in advance.:wink:
 
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Because of the internal resistance R the voltage that is available to be applied to a load resistance R (power matching conditions) is only E/2. Thus: Power=(E/2)^2/R.
 

You mean there are two resistances with value R?

---------- Post added at 08:24 ---------- Previous post was at 08:22 ----------

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The maximum power available into a load is when the load resistance equals the source resistance. So, to find the maximum power available into a load resistor you need to consider two resistors in your calculations - the source resistor and the load resistor.

Keith
 
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