Calculate the quantity of heat produced in a 20 Ω resistor carrying 2.5 A current in 5 minutes.

Given: R = 20 Ω, I = 2.5 A, t = 5 minutes = 5 × 60 = 300 s

Heat produced, H = I²Rt = (2.5)² × 20 × 300 = 6.25 × 20 × 300 = 125 × 300 = 37 500 J

Quantity of heat produced = 37 500 J (37.5 kJ)

Convert the time to seconds before anything else. The joule is defined per second, so leaving t as 5 gives 625 J — out by a factor of 60.

The current is SQUARED. Using 2.5 instead of 6.25 gives 15 000 J. If you are given current and resistance, H = I²Rt is the form to reach for; if you are given voltage and resistance, use H = V²t/R; with voltage and current, H = VIt. All three are the same law, and picking the one that matches the data you were given saves a step.