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Stormy Knight
Stormy Knight asked in Science & MathematicsPhysics · 1 decade ago

Physics Power Question ?

Why is P sometimes equal to IV and sometimes I^2R

Yet in some cases IV NOT EQUAL TO I^2R

2 Answers

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  • billrussell42
    Lv 7
    1 decade ago
    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
    1 decade ago

    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.

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