Science (086) — AI-generated practice question

Joule's Law of Heating: The heat produced in a resistor is directly proportional to (i) the square of current (I²), (ii) the resistance (R), and (iii) the time (t) for which current flows.
$$H = I^2 R t$$

Calculation:

Given: R = 25 Ω, V = 200 V, t = 30 min = 30 × 60 = 1800 s

Current, $I = \dfrac{V}{R} = \dfrac{200}{25} = 8$ A

Heat produced:
$$H = I^2 R t = (8)^2 \times 25 \times 1800$$
$$H = 64 \times 25 \times 1800 = 28,80,000 \text{ J} = 2.88 \times 10^6 \text{ J}$$

Source: Chapter 11, Section 11.7 (Heating Effect of Electric Current)

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• The law statement must mention all three factors (I², R, t) — each is a potential 1-mark point.
• First find current using Ohm's law (V = IR), then apply H = I²Rt. Convert minutes to seconds.
• Final answer 2.88 × 10⁶ J must be clearly stated. Leaving units out or forgetting the conversion of time are the most common errors.