Joule's law describes the relationship between heat generated in a conductor and which electrical quantity?

• A. Voltage times current
• B. Current squared times resistance
• C. Current times resistance
• D. Charge times energy

Answer: (B)

Heat produced in a resistor comes from the electrical energy being dissipated as the charges collide with atoms. The rate at which this heat is generated, i.e., the power converted to heat, is described by P = I^2 R. Over a period of time, the total heat Q is Q = I^2 R t. So the heat generated depends on the current squared and the resistance.

That’s why current squared times resistance is the best choice. Voltage times current is the overall electrical power and, via V = IR, is related to I^2 R, but the direct expression for heat generation in terms of the resistor’s properties is I^2 R. Current times resistance gives voltage, not heat, and charge times energy isn’t the right relationship here.