Question
(a) Fig. 6.1 shows a cross-section of the inside of an electric oven.
The heater is switched on.
(i) On Fig. 6.1, draw two arrows to show how thermal energy moves throughout the oven by convection.
(ii) Explain how thermal energy moves throughout the oven by convection. Use your ideas about density and expansion.
(iii) Use a word from the box to complete the sentence.
conduction expansion insulation radiation
Thermal energy travels at the speed of light by…………………………………………………………………………………….
(b) The oven is in a kitchen that is fitted with a smoke detector.
Warm, moving air can carry smoke particles.
Suggest the best position for the smoke detector in the kitchen.
Answer/Explanation
Answer:
(a)(i) arrow upwards from heating element
arrow across top OR down on opposite side
(a)(ii) warm air expands
(air) becomes less dense
(air) rises
(a)(iii) radiation
(b) on ceiling
Question
A thermometer is used to measure the temperature inside a room in a house.
(a) State a physical property that varies with temperature and can be used in a thermometer.
(b) Fig. 6.1 shows how the temperature of the room changes between 6:00 pm and 11:00 pm.
A heater in the room is switched on at 6 pm. The room has a large window. A large amount of thermal energy is transferred through the window. The window in the room has thick curtains. Closing the curtains reduces the loss of thermal energy from the room.
(i) Suggest the time at which the heater is switched off.
(ii) Suggest the time at which the curtains were closed and explain your answer. Use information from the graph.
time …………………………………………………………………………………………………………………..
explanation ……………………………………………………………………………………………………….
(c) In cool climates, people use mineral wool to reduce heat loss from houses. Mineral wool is made of fibres and trapped air, as shown in Fig. 6.2.
Use words from the box to complete the sentences. Each word may be used once, more than once, or not at all.
conductor conduction convection emitter insulator radiation radiator
Air is a good …………………………………….. .
When air is trapped between fibres, it reduces heat loss by ………………………………. and by …………………………………. .
Answer/Explanation
Answer:
(a) expansion / voltage / potential difference / emf
length / colour / pressure / volume / resistance / density
(b)(i) 8:30 pm
(b)(ii) 9:00 pm
(explanation) Slope / gradient of graph is less
or temperature drops / falls (more) slowly / slower
(c) insulator
conduction
convection