Topic 6 Practice Paper: Thermal physics — mark scheme (print)

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QQ/IGCSE-PHYS/T6

IGCSE · Cambridge IGCSE Physics (Extended (Core + Supplement))

Mark scheme

Thermal physics

Topic 6 Practice Paper · Maximum mark: 30

Notes for markers

Award one mark for each point marked [1], up to the marks shown for the part.
Accept answers worded differently that show the same understanding.
Units are required where the answer line shows one. ecf: allow an error carried forward.

Section A: Multiple-choice questions[10 marks]

Question	Answer and marking points	Marks
	Total for Question 1	1
	Total for Question 2	1
	Total for Question 3	1
	Total for Question 4	1
	Total for Question 5	1
	Total for Question 6	1
	Total for Question 7	1
	Total for Question 8	1
	Total for Question 9	1
	Total for Question 10	1

Section B: Structured questions[20 marks]

Question	Answer and marking points	Marks
11(a)	Brownian motion [1]	1
11(b)	The invisible air molecules move fast and randomly, bombarding each smoke speck from all sides; uneven numbers of impacts from moment to moment push the speck in changing directions. air molecules collide with the specks [1] impacts are uneven/random so the speck jitters [1]	2
11(c)	That air is made of tiny particles in constant random motion — the kinetic particle model. evidence for the kinetic particle model [1]	1
11(d)	Microscopic particles (as opposed to the molecules or atoms of the air). [1]	1
	Total for Question 11	5
12(a)	E = Pt = 42 × 600 = 25 200 J. time converted to 600 s [1] 25 200 J [1]	2
12(b)	Δθ = ΔE/(mc) = 25 200 ÷ (2.5 × 900) = 25 200 ÷ 2250 = 11.2 °C. rearranged Δθ = ΔE/(mc) [1] 11.2 °C [1]	2
12(c)	Some of the electrical energy heats the surroundings (air, insulation) instead of the block, so the block receives less than 25 200 J. energy lost to surroundings / heater [1] so the block receives less energy [1]	2
	Total for Question 12	6
13(a)	27 °C = 300 K; 12 °C = 285 K. 300 K and 285 K [1]	1
13(b)	Cooler particles move more slowly, so they hit the can’s walls less often and with less force — the force per unit area (pressure) decreases. particles slower [1] fewer/weaker wall collisions → lower pressure [1]	2
13(c)	It would fall towards zero as the particles’ kinetic energy falls towards its minimum at absolute zero (−273 °C). pressure falls towards zero at −273 °C [1]	1
	Total for Question 13	4
14(a)	Air touching the tea’s surface is warmed, expands, becomes less dense and rises; cooler denser air sinks and replaces it, carrying energy away in a convection current. warm air expands / less dense and rises [1] cooler air replaces it, circulating [1]	2
14(b)	It reduces radiative transfer: the shiny surface reflects the infrared back towards the tea instead of absorbing and re-emitting it, so less radiation escapes. shiny surface reflects infrared [1] so less radiation leaves the tea [1]	2
14(c)	Matt black is a better absorber of radiation than shiny silver, so it takes in the tea’s radiated energy faster. matt black absorbs radiation better [1]	1
	Total for Question 14	5

— End of mark scheme —