Which quantity is not a direct part of Ohm's Law expression E = I x R?

• A. Heat energy q
• B. Current I
• C. Emf E
• D. Resistance R

Answer: (A)

Ohm's law expresses a direct relationship between voltage, current, and resistance: the voltage (or electromotive force) equals the current times the resistance. The heat energy produced by the current through the resistor isn’t a direct variable in that basic equation. It’s a consequence of the power dissipated as heat. The power is P = I^2 R (or P = VI), and the heat energy generated over a time interval t is Q = P t = I^2 R t (or Q = V I t). So heat energy is related to the current and resistance, but it isn’t one of the quantities that appears in the simple E = I R expression.