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
Question
A scientist finds that the temperature of the water at the bottom of waterfalls is greater than the temperature of the water at the tops of those waterfalls.
(a) (i) State the type of energy that falling water has because of its motion.
(ii) In one waterfall, the water falls 300 m.
Calculate the decrease in the gravitational potential energy (g.p.e.) of 1.0 kg of
water as it falls through this distance.
decrease in g.p.e. =
(ii) Assume that the increase in internal energy of the 1.0 kg of water is equal to its decrease in g.p.e.
Calculate the rise in temperature of the water. The specific heat capacity of water is 4200 J / (kg °C).
rise in temperature =
(iv) Suggest a reason why the actual increase in temperature of the water is less than the value calculated in (a)(iii).
(b) State why the thermometer used to measure the temperature of the water in the scientist’s experiment required a high sensitivity.
Answer/Explanation
Answer:
(a) (i) Kinetic
(ii) (GPE=) mgh OR 1.0 × 10 × 300
3000 J
(iii) Q = mcΔθ in any form OR Q÷mc OR 3000÷[(1.0×)4200]
0.71 °C
(iv) Energy used to heat (via air resistance) / Heat lost to surroundings
OR Energy retained as KE of water (at bottom of waterfall)
OR Sound (energy) produced.
(b) Temperature change/difference is (very) small