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JAMB Physics 2009 Question 21

Question 21

Quantity of Heat

An electric heater rated 220 V, 1000 W is immersed into a bucket full of water. Calculate the mass of water if the temperature changes from 30°C to 100°C and the current flows for 300 seconds. [specific heat capacity of water = 4200 J kg−1 K−1]

  1. A.4.28 kg.
  2. B.42.86 kg.
  3. C.1.02 kg.
  4. D.7.14 kg.
Show the answer and explanation

Answer: C (1.02 kg.)

Explanation

Heat given = Pt = 1000 × 300 = 300 000 J = mcΔθ. m = 300 000 ÷ (4200 × 70) ≈ 1.02 kg.