2020 9749 H2 Physics MS EJC Suggested

©EJC 2021 9749/H2 PHYSICS 2020 PHYSICS SUGGESTED MARK SCHEME Maximum Mark: 190 9749 October/November 2020 Paper 1 Multiple Choice Question Key Question Key Question Key 1 B 6 C 11 B 2 D 7 B 12 A 3 D 8 A 13 A 4 A 9 D 14 B 5 C 10 B 15 B 16 A 21 A 26 D 17 C 22 B 27 C 18 C 23 A 28 D 19 D 24 B 29 A 20 C 25 B 30 D Notes: Candidates found Questions 8, 16, 19, 22 and 24 more challenging. Question 8 distractor B – did not account for two ropes distractor C – confused the air densities distractor D – did not account for the weight of air inside the balloon Question 11 Takes 1 hour (3600 s) for a minute hand to complete one revolution. Question 14 Note that line MN is NOT an isothermal change. Using PV = nRT, temperature is decreasing. Question 16 Note that the energy of the oscillations reduced by E / 4 rather than to E / 4. Question 19 Single slit equation accounts for only one side of the central maximum. The width of the central maximum is double of this. Question 24 Note that the question asks for potential difference, not potential.

2 ©EJC 2021 9749/H2 PHYSICS 2020 Paper 2 Structured Questions Notes: Candidates need to take care with definitions and make sure that all detail is included, and correct scientific language is used, especially in definitions. Stronger candidates used the word ‘per’ to indicate the division of two quantities. In ‘show that’ questions, stronger candidates made each step in the logic of the proof or calculation clear in order to show how to achieve the formula or answer. Stronger responses were often short and pertinent to the question asked. Qns Marks 1(a) the cyclist exerts a forward driving force which equals in magnitude and opposite to the frictional force. B1 (weight of the cyclist is equal in magnitude and opposite in direction to the normal contact force from the horizontal ground) By Newton's 1st law, the cyclist continues at constant velocity since there is no resultant force B1 1(b) ( ) ( )( )( ) 2 D D 1 1 2 2 2 22 11 4109 m s08 8 12 03 2 c Av F cA .. v .. F ρ ρ − = = = = M1 Method 1 ( ) ( ) ( )( ) ( ) ( )( )( ) ( ) max min 1 2 2 24 2 201 2 08 7 11 03 08 9 13 03 4 1 4 2 s.f. v . .. . . . vv . ∆=  =  = − − M1 M1 Method 2 ( ) ( ) ( ) D D 11 11 22 22 1 2 00 1 01 00 2 2 22 1 2 0 32 1 2 00 1 01 00 2 11 41092 22 1 2 0 32 1 4 2 s. 0 88 . 0 f 88 cvF A vFc A . ..vv .. .. . . . . . .. ρ ρ ∆∆∆ ∆∆=+ ++ ∆= + + + = + ++  = M1 M1 111 1 m sv −±= A1 Notes: one s.f. for the final uncertainty in v

3 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks 1(c)(i) Work done = force x displacement in the direction of force Power = work done/time Power = (force ×displacement)/time Power = force × velocity B1 B1 1(c)(ii) ( )( )( )( ) 2 D 3 D 3 1 2 1 2 1 12 03 2 1 142 W 0 88 250 c Av cA P Fv .. v .. v ρ ρ = = = = = A1

4 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks 2(a) work done per unit mass in bringing a small test mass from infinity to that point in the field B1 2(b) ( )( )( ) Earth satellite Earth satellite p orbit surface Earth Earth satellite orbit surface 11 24 73 10 10 10 10 111600 6 6 J 7 60 2 7 6400 1 76 0 10 GM m GM m rr MMGm rr .. . . E − ∆ −−= =−    −  − ×× − ×× × =−  = C1 A1 2(c)(i) gravitational force provides centripetal force B1 2 2 2 2 2 k 22 1 22 GMm mv rr GMm r mv r rr GMm mvr E = ×= = × = B1 Notes: Show algebra with all the steps clearly set out . In ‘show that’ questions, all the steps are required. 2(c)(ii) ( )( )( ) ( ) k 11 24 7 10 6 67 6 0 1600 27 2 10 10 2 10 1 19 10 J E .. . GMm r . −×× = × = × = A1 2(c)(iii) equation only applicable for masses in orbit, where the only force on the satellite is gravitational force which provides the centripetal force on the surface, the centripetal force is provided by the difference between weight and normal contact force from surface on satellite. Hence the satellite is not in orbit and hence expression is not applicable M1 not correct A1

5 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks 3(a) -1 M for each wrong section 3(b) B1 for each correct section

6 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks 4(a) spreading of waves (towards geometric shadow) after passing through aperture or around an obstacle A1 Notes: Do not use “bending of waves” 4(b) • waves of same type must meet and overlap • waves from sources must be coherent (OR have constant phase difference) • if waves are transverse, they must be either unpolarised or polarised in the same plane • for good contrast, waves should have approximately same amplitudes B2 4(c)(i) ( )( ) 12 12 3 3 3 3 37 gradient 4 m 88 4 44 44 44 01 2 1 0 4 4 10 1020 10 10 10 5 3 10 D Daa y . x y (. .) . x. a . . . x . a. λλ λ λ − − − − −− = −= = =−  = = = = −× ×− × = ××× M1 A1 (2.0, 8.8) × × (1.0, 4.4)

7 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks 4(c)(ii) 2 2 source source source source 1 2 90 max of CBF 1 of first dark fringe 2 AA AA . A∝  =  +   − = I I I M1 M1 A1 5(a) ( ) ( )( )( ) ( ) 2 23 28 5 19 2 0 38 10 5 9 10 7 2 10 1 6 10 30 602 140 C Q t dQ t Anvq t nvq t . ... π π − −−  = = =      ×= ××× ×  = = I I M1 A1 5(b)(i)1. 1 62 0 Hz2 0 2f ωπ ππ= == A1 5(b)(i)2. 0 rms 90 6 4 V 22 V V . .= == A1 5(b)(ii)1. ( ) ( ) total 0 0 total 16 16 0 56 A 12 612 12 6 9 R V R .  = Ω  = + = = = + I C1 M1 A1 5(b)(ii)2. ( ) 2 2 00 2 1 22 2 24 2 W 0 56 6 0 12 2 60 0 42 24 totalI II VV. . V .V P V R . (.) . P = = = = + = + = = M1 A1

8 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks 6(a) Magnetic flux density is the force acting per unit current per unit length on a wire carrying a current that is normal to the magnetic field. Notes: marks are lost if it is stated as “unit current” instead of “per unit current”. B1 6(b) ( )( ) ( ) ( )( ) solenoid 2 wire 82 23 2 1 7 10 520 4 10 0 10 67 6 2 4 R . L A Nd d . . ρ ρπ π −− − =   ×× =  ×  = = Ω C1 C1 A1 6(c) ( ) 0 00 0 wire wire 7 3 3 4 0 1 1 2410 10 6 68 10 T 46 98 B NV N V V LR d n . . Nd R R . µ µµ µ π − − −      = = =              =   = × × ×    = I C1 C1 A1 6(d) direction of current parallel to the magnetic field generate by the solenoid zero A1 520 turns 4.0 cm 0.46 mm

9 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks Notes: “not perpendicular” does not mean parallel 7(a) a discrete packet of energy of electromagnetic radiation energy of one photon = Planck constant x frequency B1 B1 7(b) electrons in gas atoms/molecules interact with photons B1 photon energy causes electron to move to higher energy level (or to be excited) B1 photon energy = difference in energy of electron energy levels B1 when electrons de-excite, photons re-emitted in all directions B1 7(c)(i) 22 13 6 13 6 3 40 eV2 ..E .n −− = −= = A1 7(c)(ii) ( ) ( )( ) 19 19 22 34 8 19 7 13 6 13 6 1 6 10 1032 10 10 10 6 3 022 J 6 63 3 00 3 022 m 58 10 ..E. h . . .. . cE λ λ λ −− − − − −−∆= − × × ∆= × = ×× ×= = M1 M1 A1 7(c)(iii) electric potential is zero at infinity A1 electric force of attraction between positively charged nucleus and negatively charged electron decrease in potential energy as charges approach

10 ©EJC 2021 9749/H2 PHYSICS 2020 Qns Marks 8(a) assuming uniform deceleration, ( ) 22 23 222 2 185 1 0 2 0 2 2 80 0 6 17