Question
Fig. 7.1 shows a domestic hot water system.
(a) The heater is placed at the bottom of the storage tank.
(i) Name the process by which water in contact with the heater becomes hot.
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(ii) 1. Explain how the water at the top of the storage tank becomes hot. Include the word density in your answer.
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2. State the name given to this process.
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(b) Hot water storage tanks are often covered in a material such as polystyrene or a ‘jacket’ made from a woollen material.
(i) State the purpose of this covering.
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(ii) Suggest two reasons why the use of such a material is important.
1. ………………………………………………………………………………………………………………………
2. ………………………………………………………………………………………………………………………
Answer/Explanation
Answer:
(a) (i) conduction
(ii) 1. water expands when heated
density (of warm water) decreases OR reverse argument
warm water rises
2. convection
(b) (i) reduce heat losses OR to act as insulation
(ii) any two from:
• economic reason: lower costs OR cheaper OR more efficient
• environmental reason: less greenhouse gases OR maintain fuel reserves
• reason to do with system: maintain temperature of water OR less energy needed to keep water hot OR water stays hotter for longer