Heat, Temperature and Heat Transfer — O/L Science

How do I practise Heat, Temperature and Heat Transfer?

1 question with a worked solution · 6 marks

1. 2019 · Paper II · 6 marks
   Question 5 gives an electric heater of stated power warming a fixed mass of water through a stated temperature rise, with the specific heat capacity supplied. It asks you to calculate the thermal energy the water absorbs, then the time the heater takes at full efficiency, and to explain why a metal spoon in hot tea becomes hotter than a wooden one.
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   (i) Q = mcΔT = 2 × 4200 × (70 − 20) = 2 × 4200 × 50 = 420 000 J (ii) P = Q / t → t = Q / P = 420 000 / 1 500 = 280 s (iii) Metal is a GOOD conductor of heat; free electrons transfer thermal energy quickly from the hot tea to the hand. Wood is a poor conductor (insulator); it does not transfer heat quickly, so it feels cooler.
   Source: Department of Examinations, Sri Lanka — G.C.E. O/L Science 2019, Paper II, Question 5 · https://doenets.lk/pastpapers

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