Kinetic particle model of matter — Paper 4 · IGCSE Physics 0625

5 Fig. 5.1 shows some gas trapped in a metal cylinder by a piston. metal cylinder piston gas Fig. 5.1 (a) The position of the piston is fixed. The cylinder is moved from a cold room to a warm room. Explain, in terms of molecules, what happens to the pressure of the gas in the cylinder. … … … … … … [4] (b) The piston is now released. It moves to the right and finally stops. Explain these observations in terms of the pressure and the volume of the gas in the cylinder. … … … … [2] [Total: 6]

6 marks

Mark scheme: 5(a) Pressure increases B1 Molecules (of gas) move faster/their kinetic energy increases/their momentum increases B1 (Molecules) collide with walls/piston more often/more frequently OR greater (rate of) change of momentum B1 (Molecules) exert greater/more force (on wall)/hit (walls) harder B1 5(b) Pressure (of gas) falls and volume (of gas) increases B1 Initially there is a larger pressure inside than outside/atmospheric pressure OR (Piston stops when) pressure (of gas) = external/outside/atmospheric pressure B1 Total: 6

This question in 0625/41 May/June 2017

5 A footballer and a referee are discussing a puddle of water that has formed on the pitch. The footballer wears a white shirt whilst the referee wears a black shirt which, apart from its colour, is identical. Fig. 5.1 shows the two men looking at the puddle. white shirt black shirt puddle Fig. 5.1 The weather is bright and sunny. (a) State and explain how the temperature of the white shirt differs from the temperature of the black shirt. … … … [2] (b) The volume of water in the puddle is slowly decreasing. (i) Describe how two changes in the weather conditions could affect the rate at which the puddle dries. change 1 … effect … … change 2 … effect … … [2] (ii) Explain, in terms of the water molecules, what happens as the puddle dries. … … … [2] [Total: 6]

6 marks

Mark scheme: 5(a) white kit cooler OR black kit warmer M1 white poor absorber/good reflector of (IR)radiation/heat/thermal energy OR v.v. for black A1 5(b)(i) any two pairs from: more/less wind; dries quicker/slower temperature increases/decreases/sunnier/cloudier; dries quicker/slower stops/starts raining; dries quicker/slower less/more humid; dries quicker/slower B2 5(b)(ii) molecules with most (kinetic) energy (escape) OR water cools B1 escape liquid/break intermolecular bonds / molecules enter air / evaporate / become vapour B1 Total: 6

This question in 0625/43 May/June 2017

6 Fig. 6.1 shows a child releasing a balloon filled with helium. Fig. 6.1 The pressure of the helium in the balloon keeps the balloon inflated. (a) Explain how the particles of helium produce this pressure. … … … … [3] (b) As the balloon travels upwards through the atmosphere, the volume o f the helium increases. The temperature of the helium remains constant. (i) State an equation th at relates the volume of the helium to its pressure. … [1] (ii) Fig. 6.2 shows how the air pressure in the atmosphere changes with the height above ground level. 120 pressure kPa 100 80 60 40 20 0 0 2000 4000 6000 8000 height / m Fig. 6.2 1. Using Fig. 6.2, determine the pressure at ground level. Give the unit. pressure = … unit = … [2] 2. Using Fig. 6.2, determine the height at which the volume of the helium in the balloon is twice the volume at ground level. height = … [2] [Total: 8]

8 marks

Mark scheme: 6(a) molecules/they move/collide B1 molecules/they move/collide with walls B1 change of momentum OR force on area B1 6(b)(i) pV = constant OR p1V1 = p2V2 B1 6(b)(ii)1 100 (kPa) OR 1.0 × 105 (Pa) M1 Pa OR kPa A1 6(b)(ii)2 (p = )50 (kPa) C1 3700 m < p < 3900 m A1 Total: 8

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4 Fig. 4.1 shows a balloon filled with helium that is used to lift measuring instruments to a great height above the Earth’s surface. Fig. 4.1 (a) Explain, in terms of momentum, how the atoms of helium produce a force on the wall of the balloon. … … … … [3] (b) At ground level, the pressure of the helium in the balloon is 1.0 × 105 Pa. The volume occupied by the helium is 9.6 m3. The balloon is released and it rises quickly through the atmosphere. The volume occupied by the helium increases, but the temperature of the helium may be assumed to stay constant. (i) Explain, in terms of the helium atoms in the balloon, why the pressure in the balloon is smaller than at ground level. … … … [2] (ii) Calculate the pressure of the helium when it occupies a volume of 12 m3. pressure = … [2] [Total: 7]

7 marks

Mark scheme: 4(a) Atoms collide with wall (and rebound) OR atoms rebound from wall B1 (Atoms) undergo change of momentum C1 Force on wall = (total) rate of change of momentum (of atoms) OR = change of momentum (of atoms) per second OR = change of momentum (of atoms) / time A1 4(b)(i) Fewer atoms per unit volume OR density of gas less B1 Rate of collision (with walls of balloon) decreases OR Fewer collisions per unit area B1 4(b)(ii) PV = constant OR P1V2 = P2V 2 OR (P2 =) P1V1 / V2 OR 1.0 × 105 × 9.6 / 12 C1 8.0 × 104 Pa A1

This question in 0625/41 Oct/Nov 2017

4 A beaker contains water at room temperature. Fig. 4.1 shows the beaker placed on a tripod above a Bunsen burner. Fig. 4.1 The Bunsen burner is lit and the temperature of the water begins to increase. (a) The water is evaporating. (i) Describe one difference between evaporation and boiling. … … … [2] (ii) State and explain what happens to the rate at which the water evaporates as its temperature increases. … … … [1] (b) After a few minutes, the water reaches its boiling point temperature. The water continues to gain energy from the Bunsen burner. (i) State what happens to the temperature of the water in the beaker. … … [1] (ii) The specific latent heat of vaporisation of water is 2.3 × 106 J / kg. After the water reaches its boiling point, it takes 12 minutes for 0.095 kg of water to boil away. Calculate the average rate at which energy is being supplied to the water by heating. rate of energy supplied = … [3] [Total: 7]

7 marks

Mark scheme: 4(a)(i) any one of these six: • evaporation: at surface OR no bubbles form) pair 1 • boiling: throughout liquid OR bubbles form ) • evaporation: at any temperature OR no heat needed) pair 2 • boiling: at specific temperature OR heat needed ) • evaporation: affected by draught / surface area) pair 3 • boiling: not affected by draught / surface area ) B1 any one pair of points B1 4(a)(ii) (it / rate) increases AND {more molecules have enough energy to escape OR break bonds} B1 4(b)(i) remains constant B1 4(b)(ii) E = m l in any form OR (E =) m l C1 P = energy / t in any form OR (P =) energy / t C1 (P = 0.095 × 2.3 × 106 / (12 × 60) =) 300 W A1

This question in 0625/42 Oct/Nov 2017

4 (a) The molecules of most liquids are, on average, slightly further apart than the molecules of a solid. State one other difference between the molecular structures of a solid and a liquid. … … [1] (b) A glass tube passes through a stopper and into a glass flask. Fig. 4.1 shows that the flask is completely full of a liquid and that there is also some liquid in the tube. stopper glass tube glass flask liquid Fig. 4.1 The flask is immersed in a large beaker of very hot water. At first, the level of the liquid in the tube falls, but after a short time it rises. (i) Explain why, at first, the level of the liquid in the tube falls. … … … … [3] (ii) Explain why the liquid level in the tube stops falling and starts to rise. … … … [2] [Total: 6]

6 marks

Mark scheme: 4(a) molecules of solid arranged in lattice / in organised pattern / without gaps / orderly / fixed structure B1 4(b)(i) glass heated first or at first liquid not heated / does not expand / takes time (to heat up) or glass poor conductor B1 glass expands B1 capacity / volume of flask increases B1 4(b)(ii) liquid (starts to) warms up B1 liquid expands more than the solid / glass B1

This question in 0625/43 Oct/Nov 2017

4 (a) Describe the movement of the molecules in (i) a solid, … … [1] (ii) a gas. … … [2] (b) A closed box contains gas molecules. Explain, in terms of momentum, how the molecules exert a pressure on the walls of the box. … … … … … … [4] [Total: 7]

7 marks

Mark scheme: 4(a)(i) (Molecules) vibrate 1 4(a)(ii) random/haphazard/in all directions 1 Any one of: with high speed freely zig-zag in straight lines 1 4(b) (Molecules) collide with walls (of box) OR (Molecules) rebound from walls (of box) 1 Change of momentum (occurs) 1 force (on walls) = (total) change of momentum per second 1 Pressure = (total) force ÷ (total) area (of walls) 1

This question in 0625/41 May/June 2018

4 (a) Fig. 4.1 represents an atom. Fig. 4.1 Representing atoms by circles approximately the same size as in Fig. 4.1, sketch (i) on Fig. 4.2, the arrangement of atoms in a crystalline solid, [1] (ii) on Fig. 4.3, the arrangement of atoms in a gas. [1] solid gas Fig. 4.2 Fig. 4.3 (b) (i) Describe the motion of the atoms in a solid. … [1] (ii) A sculptor makes a statue from a block of crystalline rock using a cutting tool. Explain why he must apply a large force to the tool to remove a small piece of rock. … … [2] (c) A helium-filled balloon in the room of a house suddenly bursts. State and explain, in terms of atoms, what happens to the helium from the balloon after the balloon has burst. … … … [2] [Total: 7]

7 marks

Mark scheme: 4(a)(i) atoms drawn close to each other and in rows 1 4(a)(ii) atoms drawn far apart and randomly positioned 1 4(b)(i) (atoms) vibrate/oscillate 1 4(b)(ii) attractive forces between atoms/molecules (in the rock) OR energy/work to separate atoms/molecules 1 force (applied must be large enough) to overcome forces between atoms/molecules OR work/energy (large) enough to separate atoms/molecules 1 4(c) helium spreads/diffuses/moves freely/collides with air (molecules) 1 the helium atoms travel in all directions/randomly/at high speed 1 OR helium rises (1) helium has low density OR He atoms high speed (1)

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4 A beaker contains some water at room temperature. A student places a mercury-in-glass thermometer in the water with the bulb of the thermometer just beneath the surface of the water. Fig. 4.1 shows the arrangement. thermometer water Fig. 4.1 The student uses an electric fan to blow air across the open top of the beaker. She notices that the reading on the thermometer begins to decrease. (a) Explain, in terms of water molecules, why the temperature of the water at the surface begins to decrease. … … … … … [3] (b) The student places the thermometer near the bottom of the beaker. The electric fan continues to blow air across the top of the beaker. After some time, the student observes that the temperature of the water at the bottom of the beaker is decreasing. State the name of the thermal transfer method causing this and explain what is happening in the water. … … … … … [3] (c) The thermometer used in this experiment has a small range and a large sensitivity. (i) State what is meant by 1. range, … … [1] 2. sensitivity. … … [1] (ii) State and explain the effect on the range of the thermometer of using a smaller bulb that contains less mercury. … … [1] [Total: 9]

9 marks

Mark scheme: 4(a) more energetic molecules escape/evaporate B1 less energetic molecules remain B1 average kinetic energy of molecules decreases OR temperature depends on kinetic energy B1 4(b) convection B1 surface/colder water more dense OR contracts B1 (cold water) sinks OR warmer water rises B1 4(c)(i)1 difference between the maximum temperature and minimum temperature it can measure B1 4(c)(i)2 distance moved by the thread per °C OR per unit temperature change B1 4(c)(ii) (range) increases and less expansion/increase in volume (of mercury per unit temperature rise) B1

This question in 0625/43 May/June 2018

5 (a) A microscope that produces a very high magnification is used to observe the Brownian motion of smoke particles in air. Fig. 5.1(a) shows the apparatus used with the microscope. Fig. 5.1(b) represents the view through the microscope and shows one of the smoke particles being observed. smoke particle microscope air molecules light and smoke particles Fig. 5.1(a) Fig. 5.1(b) (i) On Fig. 5.1(b), draw a possible path for the smoke particle. [2] (ii) Describe how air molecules cause the smoke particle to follow the observed path. … … … … [2] (b) Fig. 5.2 shows a volume of gas in a cylinder. piston gas air at atmospheric pressure Fig. 5.2 The piston in the cylinder is free to move. The piston moves to the left when the temperature of the gas is decreased. Explain, in terms of the molecules of the gas, why this happens. … … … … … [4] [Total: 8]

8 marks

Mark scheme: 5(a)(i) path shows three or more straight line sections B1 with sudden changes of direction and at least two different lengths B1 5(a)(ii) air molecules travelling in random (directions) B1 collide with the smoke particle B1 5(b) (average) speed of the molecules decreases B1 molecules collide less often (on the piston and the walls of the cylinder) B1 smaller momentum change molecules (on collision) B1 piston now has a greater force on its right-hand side OR pressure less than atmospheric B1

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6 (a) State three factors that determine the rate of evaporation of water. 1. … 2. … 3. … [3] (b) A person climbs out of a swimming pool and stands in the open air. Explain why evaporation of water from the surface of the person’s body causes the person to feel cold. … … … … [2] [Total: 5]

5 marks

Mark scheme: 6(a) Any three from: Temperature (of liquid / water) Surface area (of liquid / water) Draught / wind / movement of air (over surface) Temperature of surroundings Humidity (of surrounding air) B3 6(b) Any two from: More energetic / faster molecules escape Less energetic / slower molecules remain OR remaining water is colder Thermal energy / heat flows from body / skin to colder water (and person feels colder) OR (for one mark each) (Evaporation requires) latent heat of vaporisation Thermal energy / heat flows from body / skin B2

This question in 0625/41 Oct/Nov 2018

7 (a) In Fig. 7.1, the small circles represent molecules. The arrows refer to the change of state from the arrangement of molecules on the left to the arrangement of molecules on the right. X Y Fig. 7.1 Complete the following by writing solid, liquid or gas in each of the blank spaces. 1. Change of state X is from … to … . 2. Change of state Y is from … to … . [2] (b) Explain, in terms of the forces between their molecules, why gases expand more than solids when they undergo the same rise in temperature. … … … … [2] (c) A cylinder of volume 0.012 m3 contains a compressed gas at a pressure of 1.8 × 106 Pa. A valve is opened and all the compressed gas escapes from the cylinder into the atmosphere. The temperature of the gas does not change. Calculate the volume that the escaped gas occupies at the atmospheric pressure of 1.0 × 105 Pa. volume = … [3]

7 marks

Mark scheme: 7(a) 1. Solid to liquid B1 2. Liquid to gas / vapour B1 7(b) (Neighbouring) molecules of solid have (strong) forces of attraction between them OR Gas molecules have no / weak forces of attraction between them B1 Easier to increase separation of gas molecules (than solid molecules) (gas expands more easily so) gas molecules move farther apart B1 7(c) PV = constant OR P1V1= P2V2 OR 0.012 × 1.8 × 106 = V2 × 1.0 × 105 C1 V2 = 0.216 m3 OR 0.22 m3 A1 (Volume of escaped gas = 0.22 – 0.012 =) 0.21 m3 B1

This question in 0625/42 Feb/March 2019

3 A cube of side 0.040 m is floating in a container of liquid. Fig. 3.1 shows that the surface of the liquid is 0.028 m above the level of the bottom face of the cube. air 0.040 m cube liquid 0.028 m valve pump Fig. 3.1 The pressure of the air above the cube exerts a force on the top face of the cube. The valve is closed. (a) Explain, in terms of air molecules, how the force due to the pressure of the air is produced. … … … … [3] (b) The density of the liquid in the container is 1500 kg / m3. Calculate: (i) the pressure due to the liquid at a depth of 0.028 m pressure = … [2] (ii) the force on the bottom face of the cube caused by the pressure due to the liquid. force = … [2] (c) The valve is opened and liquid is pumped into the container. The surface of the liquid rises a distance of 0.034 m. The cube remains floating in the liquid with its bottom face 0.028 m below the surface of the liquid. (i) Calculate the work done on the cube by the force in (b)(ii). work done = … [2] (ii) Suggest one reason why this is not an efficient method of lifting up the cube. … … [1] [Total: 10]

10 marks

Mark scheme: 3(a) (air) molecules / they move / collide B1 (air) molecules / they collide with cube / (upper) surface (of cube) / wall B1 impulse exerted (on surface) OR momentum change (of molecules) B1 3(b)(i) p = hρ g in any form OR (p =) hρ g OR 0.028 × 1500 × 10 C1 420 Pa A1 3(b)(ii) F = pA in any form words, symbols or numbers OR (F =) pA OR 420 × 4.02 OR 420 × 0.0402 OR 420 × 16 OR 420 × 1.6 × 10–3 C1 0.67 N A1 3(c)(i) W = Fd in any form words, symbols or numbers OR (W =) Fd OR 0.67 × 0.034 C1 0.023 A1 3(c)(ii) lifting liquid as well OR friction between liquid and container / pipe B1

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5 Liquids and gases are two states of matter. (a) In both boiling and evaporation, a liquid changes into a gas. (i) State two ways in which boiling differs from evaporation. 1. … … 2. … … [2] (ii) Before injecting a patient, a doctor wipes a small amount of a volatile liquid on to the patient’s skin. Explain, in terms of molecules, how this procedure cools the patient’s skin. … … … … … [4] (b) Gases can be compressed but liquids are incompressible. Explain, in terms of molecules, why liquids are incompressible. … … … [2] [Total: 8]

8 marks

Mark scheme: 5(a)(i) any two from: occurs throughout the liquid OR bubbles formed occurs at one temperature / boiling point does not produce cooling OR unaffected by draught / surface area / humidity B2 5(a)(ii) (more) energetic molecules escape (from the liquid) OR molecules gain energy and escape OR molecules overcome intermolecular forces / break bonds B1 average speed decreases OR molecules with less (kinetic) energy left behind B1 temperature of liquid decreases B1 (thermal) energy conducted / gained from skin / body OR (thermal) energy lost by skin / body B1 5(b) molecules touching OR no space between molecules B1 large (repulsive / intermolecular) forces (when moved closer) B1

This question in 0625/41 May/June 2019

4 (a) State and explain, in terms of molecules, any change in the pressure of a gas when the volume is reduced at a constant temperature. Statement … Explanation … … … … … … [3] (b) Complete Table 4.1 to give the relative order of magnitude of the expansion of gases, liquids and solids for the same increase of temperature. Write one of these words in each blank space: gas liquid solid Table 4.1 expands most expands least [2] [Total: 5]

5 marks

Mark scheme: 4(a) pressure increases B1 any two from : • molecules travel shorter (average) distance between collisions with walls NOT molecules change speed • molecules hit walls more often OR more collisions (per unit area) with walls • {greater force OR greater (rate of) change of momentum of molecules} per unit area on walls B2 4(b) 1st box gas B1 2nd box solid B1

This question in 0625/42 May/June 2019

5 (a) (i) A liquid is heated so that bubbles of its vapour rise to the surface and molecules escape to the atmosphere. State the name of this process … [1] (ii) At a lower temperature than in (a)(i), molecules escape from the surface to the atmosphere. State the name of this process … [1] (b) (i) Fig. 5.1 shows apparatus used to determine the power output of a heater. thermometer electric heater metal block Fig. 5.1 The metal block has a mass of 2.7 kg. The metal of the block has a specific heat capacity of 900 J / (kg °C). In 2 min 30 s, the temperature of the block increases from 21 °C to 39 °C. Calculate the power of the heater. power = … [4] (ii) State and explain a precaution that can be taken to improve the accuracy of the experiment. Statement … Explanation … … [2] [Total: 8]

8 marks

Mark scheme: 5(a)(i) boiling B1 5(a)(ii) evaporation B1 5(b)(i) E=mc∆T in any form OR (E=) mc∆T OR (E=) 2.7 × 900 × 18 C1 44 000 (J) A1 E=Pt in any form OR (P=) E/t OR (P= ) 43 740/150 C1 (P= ) 290 W A1 5(b)(ii) lagging/insulation/named insulator (around/on block) M1 reduction of thermal energy/heat losses A1

This question in 0625/42 May/June 2019

4 (a) Water molecules escape to the atmosphere from water boiling in a pan. Water molecules evaporate from the surface of a bowl of cool water and also escape to the atmosphere. State two ways in which boiling is different from evaporation. 1. … … 2. … … [2] (b) Fig. 4.1 shows a heater in a metal block. thermometer electric heater metal block Fig. 4.1 The power of the heater is 370 W and it is switched on for 4.0 minutes. The metal block has a specific heat capacity of 420 J / (kg °C) and a mass of 5.0 kg. Calculate the increase of temperature of the block. Assume all the thermal energy from the heater is transferred to the block. temperature increase = … [4] [Total: 6]

6 marks

Mark scheme: 4(a) Any two from: bubbles form OR occurs throughout liquid only occurs at one temperature/boiling point does not produce cooling OR not affected by surface area / humidity / draught OR does not lower KE of molecules left in the liquid. B2 4(b) E = Pt in any form OR (E) = 370 × 240 C1 = 89 000 (J) A1 E = mc∆T in any form C1 (temperature increase =) 89 000 / {5.0 × 420} = ) 42 °C A1

This question in 0625/43 May/June 2019

3 Fig. 3.1 shows a shooting competition, where air rifles fire soft metal pellets at distant targets. target air rifle Fig. 3.1 When an air rifle is fired, it exerts an impulse of 0.019 N s on the pellet. (a) Define impulse. … … [1] (b) The pellet has a mass of 1.1 × 10–4 kg. Determine: (i) the speed with which the pellet leaves the rifle speed = … [2] (ii) the kinetic energy of the pellet as it leaves the rifle. kinetic energy = … [3] (c) The pellet melts when it strikes the target. Describe how the molecular structure of the liquid metal differs from that of the solid metal. … … … … [3] [Total: 9]

9 marks

Mark scheme: 3(a) B1 3(b)(i) v = I / m or 0.019 / 0.00011 in any form words, symbols or numbers or (v =) I / m 170 m / s C1 A1 3(b)(ii) KE = ½mv2 in any form words, symbols or numbers or (KE =) ½mv2 0.50 × 0.00011 × 1702 1.6 J or 1.7 J C1 C1 A1 3(c) accept reverse comments if clearly about how the molecular structure of a solid differs from that of a liquid (molecules / they) have an irregular arrangement / not ordered / random arrangement (molecules / they) are (slightly) further apart (on average) (molecules / they are) not fixed in place B1 B1 B1

This question in 0625/41 Oct/Nov 2019

4 Solids have a fixed shape. Liquids adapt to the shape of their container. Gases fill their container. Explain in terms of forces between molecules and arrangement of molecules, why solids, liquids and gases have these properties. Solids … … … Liquids … … … Gases … … … [6] [Total: 6]

6 marks

Mark scheme: 4 Solids – molecules in lattice arrangement B1 solids – strong forces between molecules B1 liquids – molecules not fixed in place OR molecules have an irregular arrangement OR molecules (slightly) further apart (on average) than in solids OR spaces between the molecules B1 liquids – (average) forces too weak to keep molecules in a definite pattern OR forces just enough to hold molecules in the bulk of the liquid B1 gases – molecules far apart B1 gases – weak / no forces between molecules (except during collisions) B1

This question in 0625/43 Oct/Nov 2019

3 Fig. 3.1 shows gas trapped in the sealed end of a tube by a dense liquid. open end sealed end trapped gas cm3 10 20 30 40 50 60 70 dense liquid Fig. 3.1 The scale marked on the sealed end of the tube is calibrated to read the volume of gas trapped above the liquid surface. Fig. 3.1 shows that initially the volume V1 of the gas is 60 cm3. The pressure of the atmosphere is 1.0 × 105 Pa. (a) State how Fig. 3.1 shows that the pressure of the trapped gas is equal to the pressure of the atmosphere. … … [1] (b) Explain, in terms of the momentum of its molecules, why the trapped gas exerts a pressure on the walls of the tube. … … … … [3] (c) More of the dense liquid is poured into the open end of the tube. The level of the liquid surface in both the sealed and the open ends of the tube rises as shown in Fig. 3.2. The temperature of the trapped gas and atmospheric pressure both remain constant. open end 15 cm sealed trapped gas end cm3 10 20 30 40 50 60 70 dense liquid Fig. 3.2 (i) In the sealed end of the tube, the volume V2 of the trapped gas is 50 cm3. In the open end of the tube, the liquid surface is 15 cm above the new level in the sealed tube. Calculate the pressure p2 of the trapped gas. pressure p2 = … [2] (ii) Calculate the density of the liquid in the tube. density = … [2] [Total: 8]

8 marks

Mark scheme: 3(a) liquid levels in the two limbs of the tube are equal B1 3(b) molecules collide with the walls (of the container) B1 momentum of molecules changes (reverses) B1 this causes a force AND force spread out (over area of walls) B1 3(c)(i) (p2 =) p1V1 / V2 = 1.0 × 105 × 60 / 50 C1 1.2 × 105 Pa A1 3(c)(ii) p2 = patm + hρg OR 1.2 × 105 – 1.0 × 105 OR 2.0 × 104 OR (ρ =) 2.0 × 104 / (0.15 × 10) C1 1.3 × 104 kg m–3 A1

This question in 0625/41 May/June 2020

4 (a) Describe, in terms of molecules, what happens when a liquid evaporates. … … … … … … [4] (b) Fig. 4.1 shows wet clothes drying on a washing line in an outside area. washing line Fig. 4.1 State two changes in the weather that help the wet clothes to dry more quickly. 1. … 2. … [2] [Total: 6]

6 marks

Mark scheme: 4(a) molecules escape from the surface of the liquid B1 more energetic / faster moving molecules escape B1 slower / less energetic molecules are left behind B1 temperature of liquid decreases because average K.E. of remaining molecules is lower B1 4(b) any two from: air temperature increases more wind cloud stops covering the Sun B2

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4 A large test-tube contains a liquid at room temperature. An electric heater is immersed in the liquid and is switched on. Thermal energy is supplied to the liquid by the heater. The temperature of the liquid increases until it reaches its boiling point. The liquid then starts to change into gas. (a) Describe, in terms of molecules and their motion, how a liquid differs from a gas. … … … … … [3] (b) Describe what happens to molecules of the liquid as its temperature begins to increase. … … … [2] (c) (i) Explain, in terms of molecules, why a supply of thermal energy is needed to change the liquid into a gas. … … [1] (ii) The density of the liquid in the test-tube is 0.86 g / cm3. The volume of liquid in the test- tube is 50 cm3. The liquid reaches its boiling point. It now absorbs 18 000 J of thermal energy and all of the liquid changes into a gas. Calculate the specific latent heat of vaporisation of this liquid. specific latent heat = … [3] [Total: 9]

9 marks

Mark scheme: 4(a) molecules close(r) B1 molecules move only small distances (between collisions) or do not move freely B1 molecules move in clusters or slide past each other B1 4(b) molecules (in liquid) move faster or gain energy B1 molecules move apart (on average) B1 4(c)(i) molecules overcome forces / gain potential energy as the liquid boils B1 4(c)(ii) (m =) ρV (in any form) or 0.86 × 50 or 43 (g) C1 (lv =) Q ÷ m (in any form) or 18 000 / 43 or 18 000 / (0.86 × 50) C1 420 J / g or 4.2 × 105 J / kg A1

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4 In Fig. 4.1, the circles represent molecules in different states of matter. A B C Fig. 4.1 (a) Identify the states A, B and C. A ……………………………………………………….. B ……………………………………………………….. C ……………………………………………………….. [2] (b) Explain, in terms of forces between molecules, why gases expand more than liquids when they have the same rise in temperature. Assume that the pressure remains constant. … … … [2] (c) Fig. 4.2 shows a cylinder and piston. cylinder piston gas Fig. 4.2 The volume of gas in the cylinder is 3400 cm3. The pressure of the gas in the cylinder is 0.90 × 105 Pa. (i) The piston is moved to the left and fixed in a new position. The pressure of the gas in the cylinder increases to 2.5 × 105 Pa. Assume that the temperature of the gas does not change. Calculate the new volume of the gas. volume = … [3] (ii) The gas in the cylinder is now heated. The piston remains fixed in the same position as in (c)(i). State and explain, in terms of molecules, any change in the pressure of the gas. statement … explanation … … [3] [Total: 10]

10 marks

Mark scheme: 4(a) A liquid B solid C gas B2 4(b) average distance between molecules greater (in gas) B1 (attractive) forces between molecules lower or zero in gas B1 4(c)(i) p1V1 = p2V2 in any form OR 0.9 × 105 × 3400 = 2.5 × 105 × V2 C1 (V2 = ) p1V1÷ p2 OR (V2 = ) 0.9 × 3400 ÷ 2.5 C1 1200 cm3 A1 Question Answer Marks 4(c)(ii) pressure increases B1 molecules move / collide faster OR have greater momentum B1 molecules collide more frequently (with piston) OR with greater change in momentum B1

This question in 0625/43 Oct/Nov 2020

3 (a) Explain, in terms of molecules, why liquids are very difficult to compress. … … … [2] (b) Fig. 3.1 shows a device that uses liquid pressure to lift heavy boxes. boxes cylinder piston moving oil oil pump Fig. 3.1 The boxes are lifted by pumping oil into the cylinder. The force upwards on the piston due to the oil, and the force downwards on the piston due to the air above the piston, combine to produce a constant force of 8800 N. The pressure of the air is 1.0 × 105 Pa and the cross-sectional area of the bottom surface of the piston is 0.016 m2. (i) Calculate the pressure of the oil at the bottom surface of the piston. pressure = … [3] (ii) As the boxes are lifted, the depth of the oil increases. Explain why the pump must exert an increasing pressure on the oil as the depth of the oil increases. … … … [2] (iii) Suggest one reason why the force of 8800 N in (b) cannot lift boxes of weight 8800 N. … … [1] [Total: 8]

8 marks

Mark scheme: 3(a) molecules (already very) close / touching B1 (repulsive) forces (very) large B1 3(b)(i) 6.5 × 105 Pa A3 (p =) F / A in any form or 8800 / 0.016 or (Fair =)1.0 × 105 × 0.016 C1 5.5 × 105 or 5.5 × 105 (+ 1.0 × 105) or (1600 + 8800) / 0.016 C1 3(b)(ii) pressure due to (increased height of) oil in cylinder mentioned or pressure (in liquid) increases as depth increases B1 to keep the upwards force constant or to lift the (extra) oil or to counteract / oppose the increased pressure / force / weight of the oil B1 3(b)(iii) (initial) force has to be greater than 8800 N to start the motion or the upwards force (just) balances the weight (so no movement) or piston / oil has weight or friction (between moving parts) B1

This question in 0625/41 May/June 2021

4 An aluminium saucepan with a plastic handle contains cold water. Fig. 4.1 shows the saucepan on a hotplate. aluminium saucepan plastic handle water hotplate Fig. 4.1 (a) State why the pan is made from aluminium but the handle is made from plastic. … … [1] (b) The hotplate is switched on and, as the temperature of the water increases, the internal energy of the water increases. (i) State, in terms of molecules, what is meant by an increase in internal energy. … … [1] (ii) Explain, in terms of the atomic lattice and electrons, how thermal energy is transferred through the aluminium. … … … … [3] (iii) Eventually, the water reaches boiling point. Thermal energy from the hotplate is still being transferred to the water. Explain, in terms of molecules, the effect of this thermal energy on the water. … … … … [3] (iv) The mass of the water decreases by 0.11 kg in 300 s. The specific latent heat of vaporisation of water is 2.3 × 106 J / kg. Calculate the rate at which the water gains thermal energy. rate of gain of energy = … [3] [Total: 11]

11 marks

Mark scheme: 4(a) aluminium is a (good) conductor (of heat) and plastic is a poor conductor / does not conduct (heat) B1 4(b)(i) increase in kinetic energy of molecules or increase in potential energy of molecules B1 4(b)(ii) any three from: • atoms (touching the hotplate) / lattice vibrate (faster) • atoms pass on energy / vibration to neighbouring atoms / to other atoms by collision • atoms pass on energy to electrons • electrons hit distant atoms or electrons move (through lattice) B3 4(b)(iii) molecules escape from the liquid (as a vapour) B1 bonds broken / (attractive) forces overcome B1 molecules gain potential energy or work done (to separate molecules / break bonds / overcome forces) B1 4(b)(iv) 840 W A3 (E =) mlv in any form or 0.11 × 2.3 × 106 or 2.53 × 105 C1 (rate =) mlv / t in any form or 0.11 × 2.3 × 106 / 300 or 2.53 × 105 / 300 C1

This question in 0625/41 May/June 2021

5 Fig. 5.1 shows the structure of a liquid-in-glass thermometer. bulb glass 0 10 20 30 40 50 60 70 80 90 100°C liquid Fig. 5.1 The bulb of the thermometer is placed into a beaker of warm water. As the liquid expands, it moves along the tube. (a) Explain, in terms of molecules, why a liquid expands when heated. … … … [2] (b) Explain, in terms of molecules, why a liquid expands more than a solid when heated. … … … [2] (c) A second thermometer has a larger bulb that contains more of the same liquid than the thermometer shown in Fig. 5.1. It has a different scale. In every other way, it is identical. (i) Explain how the sensitivity of the second thermometer compares with the sensitivity of the thermometer in Fig. 5.1. … … … [2] (ii) Explain how the range of the second thermometer compares with the range of the thermometer in Fig. 5.1. … … [1] (d) (i) State one everyday problem that is a result of thermal expansion. … … [1] (ii) Suggest and explain one way of solving this problem. … … … [2] [Total: 10]

10 marks

Mark scheme: 5(a) molecules / they speed up or gain kinetic energy B1 molecules move further apart or push others away B1 5(b) forces between liquid molecules weak(er than in solids) B1 less energy / work done to separate molecules or greater separation for same work done / same increase in energy B1 5(c)(i) greater sensitivity B1 volume increase (of liquid in second thermometer) is greater or liquid moves a greater distance (for the same temperature increase) B1 5(c)(ii) smaller range and either of: • smaller temperature increase for liquid / meniscus to reach end of tube • expands more / greater sensitivity and tube of same length B1 5(d)(i) statement of problem (e.g. bridges buckle (in hot weather)) B1 5(d)(ii) suggested solution to problem stated in 5(d)(i) (e.g. allow gaps at the ends of the bridge) B1 more detail (e.g. as the bridge expands the gaps close) B1

This question in 0625/41 May/June 2021

4 (a) Pollen particles are mixed into a liquid. They are seen to move when observed through a microscope. (i) Describe this movement. … [1] (ii) Explain this movement in terms of the molecules of the liquid and the pollen particles. … … … [3] (b) (i) Medical professionals sometimes rub ethanol over the skin of a patient. Ethanol evaporates readily at room temperature and has a high specific latent heat of vaporisation. State whether the patient experiences heating, cooling or neither at the site where the ethanol is applied. Explain your answer. statement … explanation … … … [3] (ii) State any effect on the rate of evaporation of ethanol when a fan blows air over the patient’s skin. … [1] [Total: 8]

8 marks

Mark scheme: 4(a)(i) random / haphazard / zig-zag / irregular B1 4(a)(ii) (liquid / water) molecules move fast OR (pollen) particles massive B1 collide / bombard B1 uneven collisions / collisions from different directions (cause random movement) OR (liquid / water) molecules move randomly B1 4(b)(i) cooling B1 (thermal) energy used / needed to evaporate (ethanol) / overcome attractive forces(between molecules / particles) B1 thermal energy taken from skin / patient / person B1 alternative route for last two m.p.s more / most energetic (liquid) molecules / particles escape OR less / least energetic (liquid) remain (B1) less / least energetic molecules / particles linked to lower temp (of skin) (B1) 4(b)(ii) greater / increases / faster / higher B1

This question in 0625/42 May/June 2021

4 (a) (i) Define specific latent heat of fusion. … … [2] (ii) A cup of water contains 250 cm3 of water at a temperature of 0 °C. An identical cup contains 250 cm3 of a mixture of ice and water at a temperature of 0 °C. The temperature of the surrounding air is 20 °C. State and explain which cup contains the liquid with the lower temperature after 10 minutes. statement … explanation … … [2] (b) (i) On a hot day, sweat forms on a person’s skin and then evaporates. Explain, in terms of molecules, how the evaporation of sweat cools the person. … … … … … [3] (ii) Explain why this process is more effective when a wind is blowing. … … [1] [Total: 8]

8 marks

Mark scheme: 4(a)(i) Energy transferred when 1 kg / unit mass of a substance freezes or melts A2 Energy transferred when a substance freezes/melts/changes state C1 4(a)(ii) cup containing mixture of ice and water M1 mixture of ice and water will remain at 0 °C until all ice is melted (but temperature of water at 0 °C rises) or reverse argument OR energy needed for change of state so temperature doesn’t rise until this has taken place A1 4(b)(i) in evaporation more – energetic / faster moving molecules / molecules with high(er) kinetic energy escape (from surface) B1 low(er) energy / slow molecules remain OR so remaining liquid is cooler B1 thermal energy is taken from person to liquid (so person cools down) B1 4(b)(ii) (great(er) / fast(er) evaporation of sweat as) wind blows fast moving molecules away OR molecules do not re-enter the liquid B1

This question in 0625/43 May/June 2021

2 A student carries out an experiment using a plastic beaker that contains 0.24 kg of water at 17 °C. The thermal capacity (heat capacity) of the beaker is negligible. (a) Define thermal capacity. … … … [2] (b) Several ice cubes are at a temperature of 0 °C. The ice cubes are dropped into the water and the internal energy of the water decreases. (i) Give a simple molecular account of this decrease in internal energy. … … … [2] (ii) The specific heat capacity of water is 4200 J / (kg °C). Calculate the decrease in the internal energy of the water as its temperature decreases from 17 °C to 0 °C. decrease in internal energy = … [2] (c) As the temperature of the water decreases, some of the ice melts. (i) Explain why this ice melts. … … … [2] (ii) Describe how to determine the specific latent heat of fusion of ice using this experiment. State any other measurements that the student needs to make. … … … … … [3] [Total: 11]

11 marks

Mark scheme: 2(a) (quantity of thermal) energy or energy (to increase temperature) or energy (transferred by heating) C1 energy to increase temperature (of an object) per degree Celsius 1 °C A1 2(b)(i) (internal energy) depends on kinetic energy (of molecules) B1 kinetic energy (of molecules) decreases or potential energy (of molecules) decreases B1 2(b)(ii) (ΔE =) mcΔT in any form or 0.24 × 4200 × 17 C1 1.7 × 104 J A1 2(c)(i) k.e. of molecules / (thermal) energy absorbed (from water / surroundings) or energy absorbed from (cooling) water B1 supplies latent heat or energy used to overcome intermolecular forces / to break bonds B1 2(c)(ii) any determination of mass B1 determine change in mass (of ice) / increase in mass of water or dry the ice or ensure water is at 0 °C / equilibrium is established or insulate the beaker B1 use (lf =) E / m in any form B1

This question in 0625/41 Oct/Nov 2021

3 Fig. 3.1 shows a balloon inflated with air. Fig. 3.1 The pressure of the air at the inner surface of the balloon keeps the rubber stretched. (a) Explain, in terms of the momentum of the molecules, why there is a pressure at the inner surface of the balloon. … … … … [3] (b) The volume of the air in the balloon is 630 cm3 and the pressure of the air in the balloon is 1.0 × 105 Pa. The balloon is tied to a heavy stone and dropped into a lake. The balloon is pulled down quickly and the temperature of the air inside does not change. (i) Calculate the volume of the air when the pressure of the air is 1.4 × 105 Pa. volume = … [2] (ii) The balloon and stone stop moving when the stone hits the bottom of the lake. The temperature of the air now begins to decrease. Explain why the volume of the air in the balloon decreases as the temperature decreases. … … … … [2] [Total: 7]

7 marks

Mark scheme: 3(a) any three of: they / molecules collide with inner surface momentum (of a molecule) changes / reverses force exerted / impulse force spread over area / surface or p = F / A B3 3(b)(i) (V2 =) p1V1 / p2 in any form or 630 × 1.0 × 105 / 1.4 × 105 C1 450 cm3 or 4.5 × 10–4 cm3 or 0.45 dm3 A1 3(b)(ii) any two of: molecules move more slowly / have less kinetic energy pressure (inside balloon) decreases or pressure is directly proportional to temperature or p ∝ T volume is directly proportional to temperature or V ∝ T molecular collisions less frequent molecular collisions less violent / hard / exert smaller impulse water / external pressure compresses balloon or water pressure greater (and balloon compressed) B2

This question in 0625/41 Oct/Nov 2021

4 Explain what happens to the pressure of a constant volume of air when the temperature of the air increases. Use ideas of momentum of molecules in your explanation. … … … … … … … [4]

4 marks

Mark scheme: 4 B4 (temperature of air increases) so molecules move faster / their KE increases B1 molecules collide with walls of container and change momentum B1 greater change of momentum when temperature is higher OR collisions more frequent OR harder collisions OR force = rate of change of momentum B1 (higher force and hence) higher pressure B1

This question in 0625/43 Oct/Nov 2021

3 During a picnic on a warm, dry day, a metal can of lemonade is wrapped in a damp cloth. Evaporation cools the water in the cloth. (a) Explain, in terms of molecules, how evaporation cools the water in the cloth. … … … … [3] (b) As the water in the cloth cools, so does the lemonade. Explain how electrons transfer thermal energy through the metal of the can. … … … … [3] [Total: 6]

6 marks

Mark scheme: 3(a) fast(er) / high(er) speed / (more) energetic molecules escape (into air) B1 average speed / average kinetic energy of molecules decreases B1 temperature related to speed / energy of molecules or slow(er) / low(er) speed / less energetic molecules remain (in water) B1 3(b) any three from: atoms / ions vibrate (vibrating) atoms / ions hit electrons electrons propelled / travelling through metal / moving through metal electrons hit (distant) atoms free electrons / delocalised electrons mentioned B3

This question in 0625/41 May/June 2022

6 Fig. 6.1 shows a road next to the sea. Fig. 6.1 (a) On a sunny day, the Sun warms the road. Describe how energy from the Sun reaches the Earth and warms the road. … … … … [3] (b) The temperature of the road is greater than the temperature of the sea. The surface of the road is black. Suggest one reason why the temperature of the road is greater than that of the sea. … … [1] (c) The air above the road is heated by the warm road. (i) Describe how this affects the molecules of the air. … … … [2] (ii) A cyclist travelling along the road notices that a cool breeze is blowing from the sea to the land. Explain how convection produces this breeze. You may include a diagram if it helps your answer. … … … … [3] [Total: 9]

9 marks

Mark scheme: 6(a) any three from: radiation light / infrared / electromagnetic (radiation) travel through space / vacuum absorbed by road B3 6(b) road / black surfaces are good absorbers (of radiation) or sea is a poor absorber (of radiation) B1 6(c)(i) they / molecules speed up or gain kinetic energy B1 they / molecules move further apart B1 6(c)(ii) density (of air above road) decreases or density (of hot air) decreases B1 air (above land / road) rises or air (that is hot) rises B1 air (above road) replaced by cool air / air from above sea B1

This question in 0625/41 May/June 2022

4 (a) Fig. 4.1 shows apparatus used to observe the motion of smoke particles (Brownian motion). microscope glass cover smoke glass cell Fig. 4.1 The glass cell has light shining on it from the side. The smoke particles are seen as bright specks of light when looking through the microscope. (i) Draw the path of one of the bright specks of light. [2] (ii) Explain, in terms of forces and the motion of air molecules, the cause of the motion of the smoke particles. … … … … … [4] (b) The temperature of the air in a sealed glass container is increased. (i) Explain, in terms of molecules, why the internal energy of the air increases. … … [1] (ii) Explain, in terms of molecules, why the pressure of the air also increases. … … … [2] [Total: 9]

9 marks

Mark scheme: 4(a)(i) zig zag motion / random changes of direction B1 random length of path in each direction B1 Question Answer Marks 4(a)(ii) any four from:  air molecules bombard smoke particles  air molecules are small (compared to smoke particles) / have small(er) mass  air molecules are very fast moving  air molecules move in random directions  (collisions exert unbalanced) forces on smoke particles B4 4(b)(i) kinetic energy (and potential energy) of molecules increase (hence internal energy increases) B1 4(b)(ii) bigger change in momentum of molecules OR molecules hit (the walls) harder B1 (molecules hit) more often / more frequently B1

This question in 0625/43 May/June 2022

4 A quantity of gas is trapped by a piston in a cylinder with thin metal walls. The piston is free to move without friction within the cylinder. Fig. 4.1 shows the cylinder and piston. gas cylinder piston Fig. 4.1 The cylinder is placed inside a freezer. (a) The air in the freezer is at atmospheric pressure, which is 1.0 × 105 Pa. The area of the piston in contact with the air in the freezer is 2.4 × 10–3 m2. (i) Calculate the force exerted on the piston by the air in the freezer. force = … [2] (ii) When the cylinder is first placed into the freezer, the temperature of the gas in the cylinder decreases and the air pushes the piston into the cylinder. Calculate the work done on the piston by the air in the freezer as the air pushes the piston a distance of 0.021 m into the cylinder. work done = … [2] (b) The initial temperature of the cylinder and the gas is 21 °C and, in the freezer, the temperature of the cylinder decreases to –18 °C. The thermal capacity of the cylinder is 89 J / °C. Calculate the change in the internal energy of the cylinder. change in internal energy = … [2] (c) When the temperature reaches –18 °C, the pressure of the gas in the cylinder is still equal to that of the atmosphere. Explain, in terms of the particles of the gas, how the pressure remains equal to its original value. … … … … … … [3] (d) As the temperature of the metal cylinder decreases, the volume of the metal decreases. The decrease in the volume of the metal is much less than the decrease in the volume of the gas. Explain, in terms of the particles of the metal, why the decrease in the volume of the metal is less than that of the gas. … … … [2] [Total: 11]

11 marks

Mark scheme: 4(a)(i) 240 N A2 F = pA in any form or 1.0  105  2.4  10–3 C1 4(a)(ii) 5.0 J A2 WD = Fx‖ or 240  0.021 C1 4(b) (–)3.5  103 J A2 E = CDT in any form or 89  (21 – (–18) or 89  (3) or 89  39 C1 4(c) B3 (as the volume decreases) the particles collide more often B1 (as the temperature decreases) the particles collide less violently B1 two effects cancel (to leave the pressure unchanged) or particles collide with walls / piston / cylinder B1 4(d) B2 (attractive) forces between (any two) particles large(r than in gases) B1 particles close(r) together (than gas particles) or particles already touching B1

This question in 0625/41 Oct/Nov 2022

5 (a) Three identical dishes, A, B and C, contain an equal volume of water. Dish A is outside in sunlight and experiences no wind during the day. Dish B is outside in sunlight and experiences a strong wind during the day. Dish C is in a dark room. Water evaporates from each dish. After 12 hours, a student measures the volume of water in each dish. Dish C contains the largest volume of water and dish B contains the smallest volume of water. Explain, in terms of particles, why the three dishes have different volumes of water. … … … … … … … [4] (b) Define specific latent heat of vaporisation. … … … [2] (c) Fig. 5.1 shows an insulating beaker, crushed ice, an immersion heater and a thermometer. thermometer to the power supply insulating immersion heater beaker crushed ice Fig. 5.1 The initial temperature of the ice is –60 °C. The immersion heater is switched on and the temperature is recorded at equal intervals of time. Fig. 5.2 shows the temperature–time graph. D temperature C B A time Fig. 5.2 Describe what occurs in each of the sections A, B, C and D. A … B … C … D … [3] [Total: 9]

9 marks

Mark scheme: 5(a) energy from the Sun transfers to / is absorbed by (water) molecules, (so KE of (water) molecules increases) B1 molecules with high(er) energy / KE / fast(er) moving molecules escape (from the surface) B1 wind removes molecules when they have left the surface (so they do not re-enter the liquid) B1 any one from: B1 • wind increases the rate of evaporation • (absorption of) energy from the Sun increases the rate of evaporation • least / less water evaporates / lower rate of evaporation from dish C • most / more water evaporates / higher rate of evaporation from dish B 5(b) energy to change 1 kg / unit mass from liquid to gas / gas to liquid (without changing its temperature) A2 energy to change from liquid to gas / gas to liquid C1 OR energy to change state of 1 kg 5(c) A: temperature (of solid / ice) increases AND C: temperature (of liquid / water) increases B1 B: solid / ice changes to liquid / water OR solid / ice melts (at constant temperature) B1 D: liquid / water changes to gas / steam OR liquid / water boils (at constant temperature) B1

This question in 0625/43 Oct/Nov 2022

4 Fig. 4.1 shows a metal pan on an electric hotplate. The pan contains 200 cm3 of water. water metal pan hotplate Fig. 4.1 The pan is heated. The temperature of the water in the pan increases. (a) Thermal energy is transferred through the metal pan by conduction. State and explain the two ways that thermal energy is conducted in a metal. … … … … … [3] (b) (i) The water boils and leaves the liquid as a gas. Explain, in terms of forces and distances between particles, why the gas occupies a much greater volume than it does as a liquid. … … … … [2] (ii) State two ways in which boiling differs from evaporation. 1 … 2 … [2] (c) The water is replaced with 200 cm3 of milk. The initial temperature of the milk is 20.0 °C. The boiling point of milk is 95.0 °C. The milk starts to boil when 60 700 J of thermal energy has been transferred to it. The density of milk is 1.03 g / cm3. Calculate the value of the specific heat capacity of milk. Give your answer to 3 significant figures. specific heat capacity = … [4] [Total: 11]

11 marks

Mark scheme: 4(a) delocalised / free / mobile electrons B1 electrons move through metal OR electrons collide with distant particles OR electrons carry energy through the metal B1 lattice vibrations transfer energy to neighbouring particles OR particles vibrate and cause nearby / adjacent particles to B1 vibrate OR vibrating particles collide with particles transferring energy 4(b)(i) (attractive) forces (between particles are much) greater in liquids (than in gases) B1 particles in gases are (much) further apart (than in liquids) B1 4(b)(ii) occurs at a fixed temperature B1 takes place throughout the liquid B1 4(c) 3.93 J / (g °C) OR 3930 J / (kg °C) A4 = m / V OR (m =) V OR 1.03  200 OR 206 SEEN (C1) c = E / m∆OR (c = ) E / m∆OR 60 700 / (206  75) OR 60700 / (1.03  200  75) (C1) (m =) 206 (g) OR (∆) = 75 (°C) (C1)

This question in 0625/42 Feb/March 2023

3 A rubber balloon is inflated with helium and sealed so that no helium escapes. The balloon is positioned immediately below the ceiling in a room. Heaters are switched on and the temperature of the air in the room increases. (a) When the heaters are first switched on, the temperature of the air immediately below the ceiling increases more quickly than the temperature of the air in the rest of the room. Explain why this happens. … … … [2] (b) The temperature of the helium in the balloon increases and as the rubber stretches, the volume occupied by the helium increases. (i) State what happens to the motion of the helium particles as the temperature increases. … … [1] (ii) As the rubber stretches and the volume of the helium increases, the pressure of the helium remains constant. Explain, in terms of the particles of helium, how the pressure of the helium remains constant. … … … … [3] [Total: 6]

6 marks

Mark scheme: 3(a) heated / hot(ter) / warm(er) air is less dense OR cool(er) air is more dense B1 heated / hot(ter) / warm(er) air rises (to ceiling displacing cooler air) OR cool(er) air falls (displaced by warm(er) air) B1 3(b)(i) speed / velocity (of particles) increases OR (they) move faster B1 3(b)(ii) (higher temperature means) particles collide (with rubber) harder / with more force / with greater momentum (change) B1 (larger volume means) particles collide (with rubber) less frequently OR (larger volume means) larger (surface) area (for particle collisions) B1 effect of larger volume cancels effect of increased temperature / owtte OR the effect of larger area cancels the effect of larger force / owtte OR P = F / A so the two changes cancel each other / owtte B1

This question in 0625/41 May/June 2023

4 (a) The temperature of a fixed mass of gas at constant volume is decreased. State and explain, in terms of particles, how the pressure of the gas changes. … … … … [3] (b) (i) State the value of absolute zero in °C. value of absolute zero = … °C [1] (ii) Explain what is meant by the term absolute zero. Refer to particles in your answer. … … … [2] (c) Cylinder 1 contains 350 cm3 of gas at a pressure of 9.0 × 104 Pa. The gas is transferred to cylinder 2 and the pressure increases to 1.6 × 105 Pa. The temperature remains constant. Calculate the volume of cylinder 2. volume = … [3] [Total: 9]

9 marks

Mark scheme: 4(a) pressure decreases AND particles have smaller velocity / momentum / smaller EK / kinetic energy (when temperature is lower) B1 lower rate / frequency of collision of particles B1 particles collide with smaller force OR smaller impulse change B1 Question Answer Marks 4(b)(i) –273 (°C) B1 4(b)(ii) (temperature at which) particles have least EK / kinetic energy B1 lowest possible temperature B1 4(c) 200 cm3 A3 pV = constant OR 9.0  104  350 = 1.6  105  V2 C1 V2 = [9.0  104  350] / 1.6  105 OR V2 = 2.0  10N OR 1.97  10N C1

This question in 0625/42 May/June 2023

3 Liquids are difficult to compress whereas gases can be compressed easily. (a) Explain, in terms of particles, why it is difficult to compress liquids. … … … [2] (b) Fig. 3.1 shows a rectangular block floating in water. The density of the water is 1000 kg / m3. rectangular block atmosphere water 0.087 m base Fig. 3.1 The area of the base of the block is 0.014 m2. The base of the block is at a depth of 0.087 m below the surface of the water. (i) Show that the pressure due to the water at the base of the block is approximately 850 Pa. [2] (ii) Calculate the force F on the base of the block caused by the pressure given in (b)(i). F = … [2] (iii) Force F is equal to the weight of the block. Calculate the mass of the block. mass = … [2] [Total: 8]

8 marks

Mark scheme: 3(a) particles (of liquid) are touching / close to each other B1 forces (of repulsion) between particles (of liquid) are large B1 3(b)(i) (p =) g()h B1 1000  9.8  0.087 OR (p =) 852.6 (Pa) B1 3(b)(ii) 12 N A2 p = F / A OR (F =) pA OR 850  0.014 C1 3(b)(iii) 1.2 kg A2 g = W / m OR (m =) F / g OR 12 / 9.8 C1

This question in 0625/41 Oct/Nov 2023

2 Fig. 2.1 shows an electric tumble dryer used to dry wet clothes. drum hot air blows into drum clothes heating element cool air condenser leaves condenser water Fig. 2.1 (a) Hot air blows into the drum. The air gains water vapour from the clothes and then leaves the drum. The moist air enters the condenser. Cool air leaves the condenser, passes through the heating element and enters the drum again. (i) State the process by which the hot air removes water from the wet clothes. … [1] (ii) The air is cooled as it passes through the condenser. Describe and explain one other way in which the air leaving the condenser is different from the air entering the condenser. description … explanation … … [2] (b) The drum of the tumble dryer rotates, lifting up the wet clothes which then fall down through the hot air. (i) Name the force that causes the clothes to fall down. … [1] (ii) When the drum rotates too fast the clothes remain in contact with the wall of the drum. State the direction of the resultant force on the clothes during the circular motion. … [1] (c) Suggest why using a clothesline to dry clothes in the open air is better for the environment than using an electric tumble dryer. … … [1] [Total: 6]

6 marks

Mark scheme: 2(a)(i) evaporation B1 2(a)(ii) air is drier B1 because water vapour has condensed / turned back to liquid in the condenser B1 2(b)(i) gravitational (force) OR weight B1 2(b)(ii) (force is) perpendicular to the motion (of the clothes) B1 2(c) uses (solar / wind) energy which is renewable OR energy (re)sources not used to generate electricity OR B1 greenhouse gases not produced OR does not use (fossil) fuels

This question in 0625/42 Oct/Nov 2023

4 Fig. 4.1 shows a bottle part-filled with water. The air inside the bottle is at the same pressure as the air outside the bottle. The bottle and its contents are at room temperature. bottle air water Fig. 4.1 (a) The temperature of the bottle and its contents are increased. (i) Explain, in terms of particles, how the air pressure inside the bottle changes as the temperature increases. … … … … [3] (ii) The lid is removed from the bottle. State and explain how the air pressure inside the bottle changes. statement … explanation … … [2] (b) The mass of water in the bottle is 0.18 kg. The specific heat capacity of water is 4200 J / (kg °C). Calculate the thermal energy needed to increase the temperature of the water by 20 °C. thermal energy = … [2] (c) Another plastic bottle is filled to the top with water. The height of the bottle is 40.0 cm. The density of water is 1.0 × 103 kg / m3. Calculate the pressure difference between the top and bottom of the water. pressure difference = … [2] [Total: 9]

9 marks

Mark scheme: 4(a)(i) any three from: B3 • increase in the (average) KE / speed of air particles • more frequent collisions of (air) particles (with bottle) • more forceful collisions of (air) particles (with bottle) • greater force per unit area gives greater pressure • volume unchanged and so pressure increases 4(a)(ii) (pressure decreases as) B1 air (particles) escape from the bottle / into the air until pressure (inside the bottle) is same as (air) pressure outside the bottle OR until pressure (inside the bottle) is same as B1 atmospheric pressure 4(b) 1.5  104 J A2 c = (∆)E / m∆𝜃 (∆E =) mc∆𝜃 OR (∆E =) 0.18  4200  20 C1 4(c) 3900 Pa A2 (∆p =) ρg(∆)h OR (∆p =) 1.0  103  9.8  0.4 OR C1 (∆p =) 1.0  103  9.8  40 OR (∆p =) 3.9  10N

This question in 0625/42 Oct/Nov 2023

3 (a) A car has a weight of 13 000 N. The car is supported by 4 tyres. The area of each tyre in contact with the road is 0.016 m2. (i) Calculate the pressure on the road due to the weight of the car. pressure = … [2] (ii) Explain, in terms of particles, why the air pressure in the tyres increases when the car travels along the road. … … … … … [4] (b) A gas cylinder contains helium gas at a pressure of 2.0 × 106 Pa. A volume of 0.026 m3 of the compressed gas is released from the cylinder into balloons. Each balloon contains 0.015 m3 of helium at atmospheric pressure (1.0 × 105 Pa). The temperature remains constant. Calculate the maximum number of balloons that can be filled. maximum number of balloons = … [3] [Total: 9]

9 marks

Mark scheme: 3(a)(i) 2.0  105 Pa OR 200 000 Pa OR 200 kPa A2 (P =) F / A OR 13 000 / (0.016  4) (C1) 3(a)(ii) Any four from: B4 • friction between road and tyre • temperature of air / tyre increases • particles (of air in tyre) move faster • particles (of air) collide harder with the walls (of the tyre) OR particles (of air) collide more frequently with the walls (of the tyre) • force (on the tyre wall) increases, AND area (of tyre) is constant (so tyre pressure increases) 3(b) (maximum number = ) 34 A3 pV = constant OR {2.0  106  0.026} = 1.0  105  V2 (C1) V2 = 0.52 (m3) OR (V2 =) {2.0  106  0.026} / 1.0  105 (C1) OR (number of balloons =) {2.0  106  0.026} / {1.0  105  0.015}

This question in 0625/42 Feb/March 2024

3 Fig. 3.1 shows a small block of ice floating in a beaker of warm water. block of ice warm water Fig. 3.1 (a) State one way in which the motion of the particles in ice differs from the motion of the particles in water. … … [1] (b) Energy is transferred from the water to the block of ice. (i) State the name of the thermal process that transfers energy from the water to the ice. … [1] (ii) Initially, there is 0.34 kg of water in the beaker. The specific heat capacity of water is 4200 J / (kg °C). Calculate the energy transferred from this water as its temperature decreases from 28 °C to 10 °C. energy transferred = … [2] (iii) The temperature of the water near the ice decreases first. Explain how convection causes the temperature of all the water in the beaker to decrease. … … … … [3] (iv) State what happens to the internal energy of the water as the temperature of the water decreases. Describe the change in terms of the energy of the particles. … … … [2] [Total: 9]

9 marks

Mark scheme: 3(a) (they / particles in ice) vibrate (about a fixed position) OR particles in water move throughout the liquid B1 3(b)(i) conduction B1 3(b)(ii) 2.6  104 J A2 c = (E / m OR (E =) mcOR 0.34  4200  18 OR 2.6  10N (J) C1 3(b)(iii) density (of water next to the ice) increases B1 cold(er) water sinks B1 warm(er) water replaces cold water OR warm(er) water rises OR making a convection current B1 Question Answer Marks 3(b)(iv) internal energy decreases AND (average) kinetic energy (of particles) decreases A2 kinetic energy decreases C1

This question in 0625/41 May/June 2024

4 (a) State two ways that evaporation differs from boiling. 1 … 2 … [2] (b) Fig. 4.1 shows part of a container used to store a mixture of liquid and gaseous oxygen. steel walls of container vacuum Fig. 4.1 The temperature of the liquid oxygen is –160 °C. (i) Determine the temperature of the liquid oxygen in K. temperature = … K [1] (ii) The container is made of steel and there is a vacuum between the inner and outer walls. The outer wall of the container is at room temperature. State two methods of thermal energy transfer that a vacuum prevents. 1 … 2 … [2] (c) Describe, in terms of particles, how a gas exerts a pressure on the walls of its container. … … … … [3] [Total: 8]

8 marks

Mark scheme: 4(a) (evaporation:) (only) at the surface OR boiling: happens throughout the liquid B1 (evaporation:) takes place at any temperature OR boiling: takes place at a specific temperature / boiling point B1 4(b)(i) 113 (K) B1 4(b)(ii) conduction B1 convection B1 4(c) particles collide with the walls / container B1 (particles) exert a force on the walls OR collision with walls produces a change in momentum (of particles) B1 pressure is force per unit area OR p = F / A OR pressure is rate of change of momentum per unit area B1

This question in 0625/42 May/June 2024

4 Fig. 4.1 shows a stainless-steel saucepan being heated on an electric cooker. The saucepan contains water. Fig. 4.1 (a) State what happens to the water particles as the water temperature increases. … [1] (b) The saucepan contains 250 cm3 of water. The specific heat capacity of water is 4200 J / (kg °C). The density of water is 1000 kg / m3. (i) Show that the mass of the water in the saucepan is 0.25 kg. [2] (ii) Calculate the energy required to increase the water temperature from 20 °C to 65 °C. energy = … [3] (iii) The heater supplies enough power to heat the water in 39 s. A student measures the time taken to heat the water as 115 s. Suggest why the actual time taken to heat the water is longer. Assume that the student takes accurate measurements. … … [1] (c) The stainless-steel saucepan is replaced with an aluminium saucepan of the same mass. It contains the same volume of water. The specific heat capacity of stainless steel is 500 J / (kg °C). The specific heat capacity of aluminium is 890 J / (kg °C). Explain how using an aluminium saucepan will affect the time taken to heat the water. … … … [2] [Total: 9]

9 marks

Mark scheme: 4(a) (average) KE of particles increases / particles move faster B1 4(b)(i)  = m / v OR (m =) v M1 1 cm3 = 1  10–6 m3 OR 250 cm3 = 2.5  10–4 m3 OR 1000  2.5  10–4 (= 0.25 kg) A1 4(b)(ii) 47000 J A3 ( =) 65 – 20 °C OR ( =) 45 °C C1 E = mc OR (E =) mc OR (E =) 0.25  4200  45 C1 4(b)(iii) thermal energy also transferred to the pan / surroundings OR thermal energy escapes from the water (as it is being heated) B1 4(c) any two from:  (aluminium saucepan) takes longer to heat the water  more (thermal) energy is needed (with aluminium pan for the same increase in temperature)  (because aluminium) has a higher specific heat capacity B2

This question in 0625/43 May/June 2024

6 (a) A car windscreen is covered in condensation (small droplets of water). Thermal energy is used to remove the droplets of water. The thermal energy is provided by three resistors on the windscreen. Fig. 6.1 shows two possible circuits for the three resistors. The three resistors are identical. 12 V car battery 12 V car battery Circuit A Circuit B Fig. 6.1 (i) Describe two advantages of using Circuit B. 1 … … 2 … … [2] (ii) Describe, in terms of the water particles, the process by which the water droplets are removed from the car windscreen using the heater. … … … … [2] (b) Fig. 6.2 shows a circuit containing two resistors, P and Q. The circuit is powered by a 12 V battery. 12 V 90 Ω P 70 Ω Q Fig. 6.2 (i) Calculate the current in resistor Q. current = … [2] (ii) Calculate the energy transferred electrically when the current calculated in (b)(i) is present in resistor Q for 5 minutes. energy = … [3] (iii) Energy is transferred from the battery by the electrical current. State the energy store in the battery. … [1] (iv) Calculate the total resistance of the circuit. total resistance = … [2] [Total: 12]

12 marks

Mark scheme: 6(a)(i) any two from: B2 • if one resistor fails / breaks the others will still work • each resistor gets the full voltage / 12 V or lower (total) resistance or higher current • higher power 6(a)(ii) any two from: B2 • evaporation / water evaporates • energy (from heater) transfers to particles OR particles gain energy (from the heater) • more energetic particles escape (from water / droplet) • particles leave from the surface (of the water / droplet) 6(b)(i) 0.17 A A2 R = V / I OR (I =) V / R OR (I =) 12 / 70 C1 6(b)(ii) 610 J OR 620 J A3 E = I  V  t OR (E =) V  I  t OR (E =) 12  0.17  300 C1 300 (s) OR 5  60 C1 6(b)(iii) chemical A1 6(b)(iv) 39  A2 1 / RT = 1 / R1 + 1 / R2 OR 1 / RT = 1 / 90 + 1 / 70 OR (RT =) 1 / (1 / R1 + 1 / R2) OR (RT =) 1 / (1 / 90 + 1 / 70) C1

This question in 0625/43 Oct/Nov 2024

4 Fig. 4.1 shows gas trapped in a cylinder by a piston. gas cylinder piston Fig. 4.1 (a) The volume of gas is 240 cm3. The piston is pushed to the left and is held in its new position. (i) The pressure of the gas increases from 1.0 × 105 Pa to 1.4 × 105 Pa. The temperature of the gas remains constant. Calculate the volume of the gas when the piston is in its new position. volume = … cm3 [3] (ii) The area of the piston in contact with the gas is 1.9 × 10–3 m2. Calculate the force exerted on the piston by the gas when the piston is held in its new position. force = … [2] (iii) The distance moved by the piston is 0.036 m. The average force exerted by the piston as it moves is 220 N. Calculate the mechanical work done by the piston. State the equation you use. work done = … [2] (b) Explain, in terms of particles, why gases can be compressed but liquids cannot. … … … [1] [Total: 8]

8 marks

Mark scheme: 4(a)(i) 170 (cm3) A3 pV = constant OR 1.0  105  240 = 1.4  105  V2 C1 (V2 =) {1.0  105  240} / 1.4  105 OR 1.7  10N C1 4(a)(ii) 270 N A2 (F =) pA OR (F =) 1.4  105  1.9  10-3 C1 4(a)(iii) (W =) Fd in words or symbols M1 7.9 J A1 4(b) distance between gas particles is much larger (than distance between liquid particles) B1 OR particles in liquid are touching AND particles in gas are far apart owtte

This question in 0625/42 Oct/Nov 2025

5 (a) There is a large puddle of water on a road. The water in the puddle evaporates. (i) Describe how evaporation from the puddle occurs. Use ideas about particles in your answer. … … … [2] (ii) State and explain one change in the weather that causes a faster rate of evaporation. Statement … Explanation … … … [2] (b) A car travels on a dry road. The driver presses the brakes. The car travels a distance before it comes to rest. This distance is called the braking distance. State and explain how the braking distance changes when the road is wet. … … … [1] [Total: 5]

5 marks

Mark scheme: 5(a)(i) particles with more (kinetic) energy escape OR fast(er) particles escape B1 (particles) escape from the surface B1 5(a)(ii) windy OR (air) temperature higher / Sun shining M1 particles that escape from surface blown away (and unable to return) A1 OR more energy given to the particles (to escape) 5(b) braking distance increases AND friction (between tyres and road) decreases B1

This question in 0625/42 Oct/Nov 2025