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Suggested Answers to 2015 A Level H2 Physics 9646 Paper 3

1a) 1. Net external force acting on the system is zero

Net torque on the system about any point is zero

bi) Equilibrium system. Ball is falling at constant speed, resultant force is zero.

ii) Not equilibrium. There is resultant force in the form of centripetal force on the satellite due to the earth. There is a constant change in direction therefore there is change in velocity.

2a) 6.33 x 10^7 m

b)Bright fringes get dimmer, dark fringes get brighter.

c)For interference pattern to be seen, a should be much smaller than d. When this condition is not met, fringes cannot be seen. When a becomes too large, the central maximun diffraction bands will not be wide enough to produce inteference pattern.

3a) 14.0ºC

b) With an increase in temperature, the resistance of the thermistor drops. This leads to a drop in the circuit’s total resistance which increases the current through the thermistor, increasing the heating on the thermistor and further lowering the resistance. When the resistance is too low, the whole process will continue and result in a thermal runway, resulting in the thermistor permanently damaged by heat.

4a) Tesla is a unit of magnetic flux density when a uniform magnetic field normal to a wire carrying a current of 1A produces a force per unit length of 1N/m

bi) Force acting on the particle is always normal to the velocity of the particle.

ii) 2.38 x 10^-21 Ns

c) *Line is downwards with a smaller curvature.

5a) A photon is a packet of energy of electromagnetic radiation

bi) 3.84 x 10^-19 J

ii) 8.36 x 10^-25 Ns

c) 52.4º

6ai) Rate of change of velocity

ii) Since the radius of earth is 6400km, several km above the earth’s surface would not affect the acceleration of free fall.

bi) Surface area of the ball is too small or distance traveled by the ball is too short.

ii) 1. 0.299 s

0.0362 s

c) 9.8%

di) The height to fall has now been decreased, thus it takes less time for the ball to travel to the point.

ii) The ball will be affected by the magnetic force exerted onto it, thus reducing the net downward force acting on the ball. As a result, the time taken will be longer.

e) Acceleration will decrease till it reaches zero. When air resistance is equal to the weight of the ball, the resultant force acting on the ball will be zero. Hence it has reached terminal velocity and acceleration is zero.

7ai) 1. 24.04 V

60.5 Hz

ii) There is a heating effect regardless of direction of the current. It depends on the root mean square current instead of the average current. The heating effect is caused by power loss.

bi) The amount of thermal energy required to raise the temperature of 1 unit mass of the substance by 1ºC

ii) This indicates the power loss from the system to the surrounding.

iii) 4.22 x 10^3 J/kg K

c) *same gradient, y-intercept should be more negative.

di) The increase in internal energy of a system is equal to the sum of the thermal energy supplied to the system and the amount of work done on the system

ii)If specific heat capacity is measured at a constant volume, no work is done on system. If specific heat capacity is measured at constant pressure, there will be a change in volume. Hence, there is work done on the gas.

8ai) An object undergoing oscillatory motion with its acceleration directly proportional to its displacement from its equilibrium position. The acceleration is always towards the equilibrium position.

ii) 1. Acceleration is always opposite in direction of displacement. Hence it is oscillating.

Acceleration is not directly proportional to its displacement. Hence, oscillations are not simple harmonic.

bi) 1. A wave in which the particles oscillates parallel to the direction of propagation.

The speed of the wave means the distance traveled per unit time by a wave front.

ii) 1. 1.20 x 10^-3

1.20 x 10^-3
3.20 x 10^-3 m/s
2.71 x 10^-31 J

iii) Sound waves moves relatively fast in gas but the gas molecules oscillate back and forth about their original positions with relatively small speeds.

ci) Energy of the wave originates from the vibrational motion of the gas molecules.

ii) It is caused by the pressure imbalance from the disturbance of the gas’ uniform density.

A-LEVEL H2 MATH JUNE HOLIDAYS IN TENSIVE REVISION

A-LEVEL H2 PHYSICS JUNE HOLIDAYS INTENSIVE REVISION