Q39 of 72 Page 12

A heater coil connected to a 220 V has a resistance of 150 ohm. How long will it take for this coil to heat 1 kg of water from 200C to 600C, assuming that all heat is taken up by water?

Mass of the water, m = 1 kg
Specific heat capacity of water, C = 4200 J / kg / 0C
Change in temperature, (t2 - t1) = 600C – 200C = 40 0C
Therefore the heat required to raise the temperature of 1 kg of water from 200C to 600C Q = mC(t2-t1)
   = 1 × 4200 × 40
  = 168000 joulesHeat produced Q = joules
i.e. 168000 =
Therefore time taken t = = 520.66 s

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