P=I^2 p=v^2/r?

given that p=I^r , and p=v^2/r ,would you want a high or low resistance or a high resistance for maximum power output, like and electric chainsaw for example.

Comments

One Response to “P=I^2 p=v^2/r?”
  1. devilsadvocate1728 says:
    July 13, 2010 at 12:10 pm

    If the source voltage has a low series resistance as is the usual case for commercial power sources, you can treat the voltage as a constant. You can also ignore the first equation P = I²R and focus on the second, P = V²/R. Dividing a constant voltage by a low number will give a higher power than dividing by a high number, so you want the resistance to be low for high power.

    In practice, for the case in which the resistance of the source is not negligible, maximum power is delivered to the load when the load resistance is equal to the source resistance – but at that point, as much power is dissipated in the source as in the load, so you can expect the wiring or something upstream to start heating up with a load like that.


 
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