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JAMB Physics 2006 Question 43

Question 43

Quantity of Heat

An immersion heater rated 2.0 A, 240 V is used to boil water from temperature 52°C to 100°C. If the mass of the water is 2.5 kg, determine the time taken to boil the water. [Specific heat capacity of water = 4.2 × 103 Jkg−1 K−1]

  1. A.1.05 × 104s.
  2. B.1.05 × 105s.
  3. C.1.05 × 103s.
  4. D.1.05 × 102s.
Show the answer and explanation

Answer: C (1.05 × 103s.)

Explanation

Heat needed = mcΔθ = 2.5 × 4200 × 48 = 504 000 J. Power = IV = 2 × 240 = 480 W, so t = 504 000 ÷ 480 = 1050 s = 1.05 × 103 s.