Sara Bentley
CAMBRIDGE IGCSE™ PHYSICS 0625/43
May/June 2025 – Paper 4 Theory (Extended)
ANSWER-FILLED VERSION
Maximum mark: 80 | Time: 1 hour 15 minutes
Answers and working are based on the June 2025 (v3) Question Paper and Mark Scheme.
Question 1 – Motion [7 marks]
|
Part |
Answer / Working |
Marks |
|
1(a) |
11.5 m s⁻¹ | 1 |
|
1(b) |
Distance = area under graph = ½(0.5)(20) + ½(3.5)(20) = 45 m. |
3 |
| 1(c) | Deceleration = Δv/Δt = 20/(4.0−0.5) = 5.7 m s⁻². |
3 |
Question 2 – Momentum and Forces [6 marks]
|
Part |
Answer / Working |
Marks |
|
2(a) |
p = mv (momentum = mass × velocity). |
1 |
|
2(b) |
Conservation of momentum: 720v + (120×7850) = 6.55×10⁶; v = (6.55×10⁶−9.42×10⁵)/720 = 7.79×10³ m s⁻¹ = 7790 m s⁻¹. |
3 |
|
2(c) |
At terminal velocity, weight = upward force = 120000 N. m = W/g = 120000/9.8 ≈ 12000 kg. |
2 |
Question 3 – Work, Energy and Power [7 marks]
|
Part |
Answer / Working |
Marks |
|
3(a) |
W = Fd, so F = 110/0.45 = 244 N ≈ 240 N. | 2 |
|
3(b)(i) |
110 = ½(0.030)v²; v = √(220/0.030) ≈ 86 m s⁻¹. |
3 |
| 3(b)(ii) | Air resistance/drag/friction acts; energy is transferred to the surroundings (thermal energy), so speed decreases. |
2 |
Question 4 – Thermal Physics [8 marks]
|
Part |
Answer / Working |
Marks |
|
4(a) |
Copper contains free/delocalised electrons. They carry thermal energy and collide with ions; lattice vibrations also transfer energy to neighbouring ions. | 3 |
|
4(b)(i) |
Thermal energy transferred per unit mass per unit temperature change. |
2 |
| 4(b)(ii) | Water gains: 50×4.2×9 = 1890 J. Metal loses: 54×c×69. Equate: 54c×69=1890, so c=0.51 J g⁻¹ °C⁻¹. |
3 |
Question 5 – Refraction [7 marks]
|
Part |
Answer / Working |
Marks |
|
5(a) |
Ratio of the speed of light in air to its speed in water; equivalently sin i/sin r. |
1 |
|
5(b) |
P continues vertically. Q refracts away from the normal in the correct direction. |
2 |
|
5(c) |
n = 1/sin49° ≈ 1.3. |
2 |
|
5(d) |
Light travels from denser water to less dense air and the incidence angle is greater than the critical angle (49°), so total internal reflection occurs. |
2 |
Question 6 – Ultrasound [6 marks]
| Part | Answer / Working |
Marks |
|
6(a) |
Sound with frequency higher than 20 kHz. |
1 |
|
6(b) |
Particle vibrations are parallel to the direction of propagation. |
1 |
|
6(c)(i) |
Send an ultrasound pulse into water; it reflects from the object; measure the time to travel to the object and back; use the speed/time relationship to determine depth (including the factor ½ for the return journey). |
3 |
|
6(c)(ii) |
Medical scanning of soft tissue. (Non-destructive testing is also accepted.) |
1 |
Question 7 – Electric Circuits [7 marks]
|
Part |
Answer / Working |
Marks |
|
7(a) |
0.50 A |
1 |
|
7(b) |
V = IR = 0.50×6.0 = 3.0 V. |
2 |
|
7(c) |
12−3.0 = 9.0 V. |
1 |
|
7(d) |
I₂=9.0/20=0.45 A; I₁=0.50−0.45=0.05 A; R=9.0/0.05=180 Ω. |
3 |
Question 8 – Electric Fields and Charge [8 marks]
| Part | Answer / Working |
Marks |
|
8(a)(i) |
A region where an electric charge experiences a force. |
1 |
|
8(a)(ii) |
Four straight radial field lines directed inward toward the negative point charge. |
2 |
|
8(b) |
Q=W/V. 4.5×10⁵ MJ = 4.5×10¹¹ J. Q=(4.5×10¹¹)/(2.9×10⁸)≈1.6×10³ C = 1600 C. |
3 |
|
8(c) |
Q=It=2.0×120=240 C. |
2 |
Question 9 – Transformers [9 marks]
| Part | Answer / Working |
Marks |
|
9(a)(i) |
AC in primary produces a changing magnetic field; soft-iron core transfers it to the secondary; changing field links/cuts the secondary, inducing an e.m.f. and alternating current. |
3 |
|
9(a)(ii) |
Vs/Vp=Ns/Np=20/1; Vs=12×20=240 V. | 2 |
|
9(b) |
P=I²R; I²=(1.25×10⁻³)/0.050=0.025; I=√0.025=0.16 A. |
2 |
| 9(c) | Less power/heating/energy loss; thinner/cheaper cables. (Fewer pylons or longer-distance transfer are also accepted.) |
2 |
Question 10 – Space Physics [8 marks]
| Part | Answer / Working |
Marks |
|
10(a) |
Distance travelled in the vacuum of space by light in one year. |
1 |
| 10(b) |
d=ct=3.0×10⁸×490=1.47×10¹¹ m≈1.5×10¹¹ m. |
2 |
| 10(c) | H₀=gradient=v/d. Using the best-fit line: (2.5×10⁴)/(100×10²⁰)=2.5×10⁻¹⁸ s⁻¹. |
3 |
|
10(d) |
Redshift is an observed increase in wavelength of electromagnetic radiation/light from distant galaxies compared with the wavelength measured on Earth. |
2 |
Question 11 – Nuclear Physics [7 marks]
|
Part |
Answer / Working |
Marks |
|
11(a) |
Time taken for half the nuclei in any sample of a radioactive isotope to decay. | 1 |
|
11(b)(i) |
²³⁴₉₁Pa → ²³⁴₉₂U + ⁰₋₁β⁻ | 3 |
| 11(b)(ii) | A neutron changes into a proton (plus an electron). |
1 |
| 11(c) | α-particles have greater kinetic energy than β-particles; α-particles also have greater electric charge than β-particles. |
2 |
Accuracy / format note: For drawing questions (5(b) and 8(a)(ii)), the required diagram content is stated explicitly in words.
