Energy Transfer Questions - GCSE Level
Q5. A vacuum flask is designed to reduce the rate of heat transfer.
(a)
(i) Complete the table to show which methods of heat transfer are reduced by each of the features labelled in the diagram. The first row has been done for you.
(2 marks)
| Feature |
Conduction |
Convection |
Radiation |
| vacuum |
|
|
|
| silvered surfaces |
|
|
|
| plastic cap |
|
|
|
(ii) Explain why the vacuum between the glass walls of the flask reduces heat transfer by conduction and convection. (2 marks)
(b) The diagram shows a gas flame patio heater.
(i) Explain why the top surface of the reflecting hood should be a light, shiny surface rather than a dark, matt surface. (2 marks)
(ii) Most of the chemical energy in the gas is transformed into heat. A small amount of chemical energy is transformed into light. Draw and label a Sankey diagram for the patio heater. (2 marks)
(iii) State why the total energy supplied to the patio heater must always equal the total energy transferred by the patio heater. (1 mark)
(5 marks total)
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