Secondary 4 Combined Science Physics Comprehension Quiz

Secondary 4 Combined Science Physics Quiz - Comprehension - ANSWER KEY

Total Marks: 40

Section A: Particle Theory and Thermal Physics (10 marks)

1. (a) [1 mark]

• Solid and liquid (melting ice/water mixture)
• Accept: "solid and liquid" or "ice and water" or "melting"

1. (b) [2 marks]

• Particles gain kinetic energy and move/vibrate faster [1 mark]
• Spacing between particles increases as liquid water expands when heated [1 mark]
• Accept: "particles move faster and spread further apart"

1. (c) [2 marks]

• Energy supplied is used to overcome the attractive forces between particles / to break bonds between particles [1 mark]
• This energy is latent heat of vaporisation; temperature remains constant during change of state from liquid to gas [1 mark]
• Accept: "energy is used to separate particles rather than increase kinetic energy"

2. (a) [1 mark]

• Conduction

2. (b) [2 marks]

• Particles at the hot end of the spoon gain kinetic energy and vibrate more vigorously [1 mark]
• These vibrations are passed to neighbouring particles through collisions, transferring energy along the spoon [1 mark]
• Accept: "free electrons in the metal also transfer energy rapidly through the metal"

2. (c) [2 marks]

• Wood is a poor conductor of heat / an insulator [1 mark]
• Particles in wood do not pass on vibrations as effectively as metal particles; fewer free electrons available for energy transfer [1 mark]
• Accept: "wood has lower thermal conductivity"

3. (a) [1 mark]

• Cup A (the metal cup)

3. (b) [2 marks]

• Metal is a good conductor of heat [1 mark]
• It transfers thermal energy from the hot water to the surroundings more quickly than the ceramic cup, which is a poorer conductor [1 mark]
• Accept: "metal has higher thermal conductivity, so heat is lost faster"

4. (a) [2 marks]

• The air particles inside the bottle lose kinetic energy as they cool, so they move slower [1 mark]
• The particles exert less pressure on the inner walls of the bottle; the greater external atmospheric pressure crushes the bottle slightly [1 mark]
• Accept: "lower temperature reduces pressure inside, so outside pressure crushes it"

4. (b) [1 mark]

• The bottle is flexible / not perfectly rigid
• Accept: "the bottle can change shape" or "the volume of the bottle can decrease"

5. (a) [1 mark]

• The bimetallic strip bends / curves
• Accept: "the strip bends towards the iron side"

5. (b) [2 marks]

• Different metals expand at different rates when heated (brass expands more than iron) [1 mark]
• Since the metals are bonded together, the unequal expansion causes the strip to bend towards the side that expands less (iron) [1 mark]
• Accept: "brass has a higher rate of thermal expansion, causing bending"

Section B: Kinematics and Forces (10 marks)

6. (a) [1 mark]

• a = Δv/Δt = (12 - 0) / 10 = 1.2 m/s²
• Accept: 1.2 m/s²

6. (b) [2 marks]

• Distance = area under velocity-time graph between 10 s and 30 s
• Area = rectangle (12 × 20) = 240 m [1 mark for correct method, 1 mark for correct answer]
• Answer: 240 m

6. (c) [2 marks]

• Total distance = area under entire graph
• Area = ½ × 10 × 12 + 12 × 20 + ½ × 20 × 12 = 60 + 240 + 120 = 420 m [1 mark]
• Average speed = total distance / total time = 420 / 50 = 8.4 m/s [1 mark]
• Answer: 8.4 m/s

7. (a) [1 mark]

• 6 N

7. (b) [2 marks]

• The block moves at constant speed, so acceleration is zero [1 mark]
• By Newton's First Law, net force = 0, therefore frictional force = applied force = 6 N [1 mark]
• Accept: "at constant speed, forces are balanced, so friction equals applied force"

7. (c) [2 marks]

• The block will accelerate / speed up [1 mark]
• Applied force (10 N) is greater than frictional force (6 N), so there is a net force of 4 N forward; by Newton's Second Law, the block accelerates in the direction of the net force [1 mark]
• Accept: "net force causes acceleration"

8. (a) [1 mark]

• Both balls hit the ground at the same time.

8. (b) [1 mark]

• In a vacuum, there is no air resistance, so both balls experience the same acceleration due to gravity (10 m/s²) regardless of mass.
• Accept: "acceleration due to gravity is constant for all objects in a vacuum"

9. (a) [1 mark]

• a = (v - u) / t = (20 - 0) / 8 = 2.5 m/s²
• Accept: 2.5 m/s²

9. (b) [2 marks]

• F = ma [1 mark for correct formula]
• F = 1200 × 2.5 = 3000 N [1 mark for correct answer]
• Answer: 3000 N

10. (a) [1 mark]

• Friction / static friction

10. (b) [1 mark]

• Up the slope / parallel to the slope (opposing the component of weight down the slope)
• Accept: "along the slope, upwards"

Section C: Waves and Optics (10 marks)

11. (a) [1 mark]

• 35° (angle of reflection = angle of incidence)

11. (b) [2 marks]

• Any two from: [1 mark each]
  • Virtual (cannot be projected on a screen)
  • Same size as object
  • Laterally inverted (left-right reversed)
  • Same distance behind mirror as object is in front
  • Upright

11. (c) [1 mark]

• Any one from:
  • Image is smaller/diminished (compared to same size in plane mirror)
  • Image covers a wider field of view
  • Image is always virtual and upright (same as plane mirror, but accept if stated with other differences)

12. (a) [2 marks]

• 1/f = 1/u + 1/v
• 1/10 = 1/25 + 1/v [1 mark for correct substitution]
• 1/v = 1/10 - 1/25 = (5 - 2)/50 = 3/50
• v = 50/3 = 16.7 cm [1 mark for correct answer]
• Answer: 16.7 cm (accept 16.7 cm or 50/3 cm)

12. (b) [2 marks]

• Any two from: [1 mark each]
  • Real
  • Inverted
  • Diminished (smaller than object)
  • Located beyond F (between F and 2F on the other side)

12. (c) [2 marks]

• The image is virtual [1 mark]
• The object is placed within the focal length (u < f); the refracted rays diverge and appear to come from a point on the same side as the object; a virtual image cannot be projected onto a screen because light rays do not actually meet at the image position [1 mark]
• Accept: "virtual image formed when object is between lens and focal point"

13. (a) [1 mark]

• The wavelength decreases.

13. (b) [1 mark]

• The speed of the wave decreases in shallow water; since frequency remains constant, wavelength must decrease (v = fλ).
• Accept: "wave speed decreases, so wavelength decreases"

14. (a) [1 mark]

• Second harmonic / first overtone
• Accept: "standing wave with two antinodes" or "second harmonic"

14. (b) [1 mark]

• The pitch increases.
• Accept: "frequency increases" or "higher pitch"

15. (a) [1 mark]

• Above 20,000 Hz / above 20 kHz
• Accept: "frequencies greater than 20 kHz"

15. (b) [1 mark]

• Ultrasound is non-ionising / does not damage living cells, unlike X-rays which are ionising and can harm the fetus.
• Accept: "ultrasound is safer than X-rays for the fetus"

Section D: Electricity and Energy (10 marks)

16. (a) [2 marks]

• P = VI
• I = P/V = 2200/240 [1 mark for correct substitution]
• I = 9.17 A [1 mark for correct answer]
• Answer: 9.17 A (accept 9.2 A)

16. (b) [2 marks]

• Q = mcΔθ
• Q = 1.5 × 4200 × (100 - 25) [1 mark for correct substitution]
• Q = 1.5 × 4200 × 75 = 472,500 J [1 mark for correct answer]
• Answer: 472,500 J or 472.5 kJ

16. (c) [2 marks]

• Electrical energy supplied = P × t = 2200 × (4 × 60) = 528,000 J [1 mark]
• Efficiency = (useful energy output / total energy input) × 100%
• Efficiency = (472,500 / 528,000) × 100% = 89.5% [1 mark]
• Answer: 89.5% (accept 89-90%)

17. (a) [1 mark]

• The black can

17. (b) [2 marks]

• Black surfaces are better absorbers of thermal radiation than white surfaces [1 mark]
• The black can absorbs more radiant energy from the Sun, converting it to internal energy, resulting in a greater temperature rise; white surfaces reflect more radiation and absorb less [1 mark]
• Accept: "black is a good absorber, white is a poor absorber/good reflector of radiation"

17. (c) [1 mark]

• Any one from:
  • Heat loss to surroundings (convection currents, conduction to table)
  • Evaporation of water cooling both cans
  • Clouds/shadows reducing sunlight intensity
  • Not perfectly identical conditions (e.g., slight difference in water mass)
  • White paint may not be perfectly reflective

18. (a) [1 mark]

• R_total = R₁ + R₂ = 4 + 6 = 10 Ω
• Answer: 10 Ω

18. (b) [2 marks]

• I = V / R_total = 12 / 10 [1 mark for correct formula/substitution]
• I = 1.2 A [1 mark for correct answer]
• Answer: 1.2 A (current is the same through both resistors in series)

19. (a) [2 marks]

• 1/R_total = 1/R₁ + 1/R₂ = 1/4 + 1/6 = 3/12 + 2/12 = 5/12 [1 mark for correct substitution]
• R_total = 12/5 = 2.4 Ω [1 mark for correct answer]
• Answer: 2.4 Ω

19. (b) [1 mark]

• Any one from:
  • Each appliance can be switched on/off independently
  • If one appliance fails, others continue to work
  • Each appliance receives the full mains voltage
• Accept any valid advantage of parallel circuits in a household context.

20. (a) [2 marks]

• Weight = mg = 2 × 10 = 20 N [1 mark for correct weight calculation]
• Work done = force × distance = 20 × 3 = 60 J [1 mark for correct answer]
• Answer: 60 J

20. (b) [1 mark]

• Power = work done / time = 60 / 4 = 15 W
• Answer: 15 W

END OF ANSWER KEY