Heat produced is proportional to the square of current strength. Which current-law statement describes this relationship?

• A. Direct current
• B. Alternating current
• C. Joule's law
• D. Ohm's law

Answer: (C)

Heat produced in a conductor comes from electrical energy being converted into thermal energy. The rate of heat generation is the electric power P, which equals VI. If the conductor has resistance R, then V = IR, so P = I^2R. This shows that for a given resistance, the heat produced per unit time is proportional to the square of the current. Over a time interval, the total heat is Q = I^2Rt. This specific relationship is Joule's law.

Direct current and alternating current describe the type of current, not the heating rule, and Ohm's law relates voltage, current, and resistance. The heating relation that ties heat to the square of current is Joule's law, applicable to both DC and AC (using RMS current for AC).