According to Joule's law of heating, the heat produced in a resistor is directly proportional to the square of: MCQ with Answer and Explanation

Explanation:
Power factor = cosφ, where φ is phase angle between voltage and current. Also, power factor = R/Z (resistance/impedance) for series circuits, and = true power (W) / apparent power (VA). Thus both (a) and (c) are correct definitions. Memory tip: 'Power factor = cosφ = R/Z = P/S; ideal = 1 (purely resistive)'. This definition question tests AC circuit knowledge, crucial for competitive exams. Always link power factor to energy efficiency: low power factor means more current for same power, increasing losses.

Explanation:
F = (9/5)C + 32. Given F = 2C: 2C = 1.8C + 32 ⇒ 0.2C = 32 ⇒ C = 160°. Verify: F = 2×160 = 320°; formula: (9/5)×160+32 = 288+32 = 320°. Memory aid: Solve linear equation for temperature conversion problems. Algebraic manipulation of scale relations frequently tested in competitive exams.

Explanation:
Volume V = (4/3)πr³, so ΔV/V = 3 Δr/r. Percentage error in volume = 3 × 2% = 6%.