Physics Power Question ?
Why is P sometimes equal to IV and sometimes I^2R
Yet in some cases IV NOT EQUAL TO I^2R
Why is P sometimes equal to IV and sometimes I^2R
Yet in some cases IV NOT EQUAL TO I^2R
billrussell42
Favorite Answer
For DC circuits, or AC circuits involving only resistances, no reactances:
P is always equal to I*V, not sometimes.
P is always equal to I²R, not sometimes
P is always equal to V²/R.
They are all the same, just substitution using Ohm's law.
For example
P = I*V but V = IR, so substituting
P = I*I*R = I²R
the other example
P = I*V but I = V/R, so substituting
P = V*V/R = V²/R
.
Anonymous
P=IV subst (V=IR) P= I^2R every time. The only time this would be wrong would be if it was AC volts and there was a reactance involved.