Specific Heat Capacity
Q1.
An electric immersion heater is used to heat the water in a domestic hot water tank.
When the immersion heater is switched on the water at the bottom of the tank gets hot.
 
(a)     Complete the following sentence.
The main way the energy is transferred through the copper wall of the water tank is
by the process of ________________________________________ .
(1)
(b)     The immersion heater has a thermostat to control the water temperature.
When the temperature of the water inside the tank reaches 58°C the thermostat switches the heater off. The thermostat switches the heater back on when the temperature of the water falls to 50°C.
Graph A shows how the temperature of the water inside a hot water tank changes with time. The tank is not insulated.
 
Time in hours
(i)      The temperature of the water falls at the fastest rate just after the heater switches off.
Explain why.
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(2)
(ii)     To heat the water in the tank from 50°C to 58°C the immersion heater transfers 4032 kJ of energy to the water.
Calculate the mass of water in the tank.
Specific heat capacity of water = 4200 J/kg°C 
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Mass = _______________________________ kg
(3)
(iii)    An insulating jacket is fitted to the hot water tank.
Graph B shows how the temperature of the water inside the insulated hot water tank changes with time.
 
Time in hours
An insulating jacket only costs £12.
By comparing Graph A with Graph B, explain why fitting an insulating jacket to a hot water tank saves money.
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(3)
(Total 9 marks)