2023 Cambridge IGCSE Physics (0625) Practice Paper with Answers

Detailed calculations: (a) Acceleration is defined as rate of change of velocity, a = (v - u) / t. (b) Using v = u + at, v = 0 + (1.5 * 4.0) = 6.0 m/s. (c)(i) The speed-time graph begins at (0 s, 0 m/s) with a straight line up to (4.0 s, 6.0 m/s). It then stays horizontal at 6.0 m/s from 4.0 s to 10.0 s. Finally, it goes down in a straight line from (10.0 s, 6.0 m/s) to (13.0 s, 0 m/s). (c)(ii) Total distance is calculated by finding the area under the speed-time graph. Area of first triangle = 0.5 * 4.0 * 6.0 = 12 m. Area of rectangle = 6.0 * 6.0 = 36 m. Area of final triangle = 0.5 * 3.0 * 6.0 = 9.0 m. Total distance = 12 + 36 + 9 = 57 m.

(a) 1 mark: change in velocity per unit time or rate of change of velocity. (b) 1 mark: correct formula or substitution (1.5 * 4.0); 1 mark: 6.0 m/s with unit. (c)(i) 1 mark: straight line from origin to (4.0, 6.0); 1 mark: horizontal line from t = 4.0 s to t = 10.0 s; 1 mark: straight line from (10.0, 6.0) to (13.0, 0). (c)(ii) 1 mark: identifying distance is area under graph or summing sections; 1 mark: 57 m.

(a) Scalars only have magnitude, whereas vectors have both magnitude and direction. Mass is a scalar and force is a vector. (b) Resultant force = Forward force - Frictional force = 18 N - 6.5 N = 11.5 N. (c) Acceleration a = F / m = 11.5 N / 3.5 kg = 3.286 m/s^2, which rounds to 3.3 m/s^2. (d) Once the pulling force is removed, friction is the only horizontal force acting. This causes an unbalanced force in the direction opposite to motion. (e) New acceleration a = F / m = -6.5 N / 3.5 kg = -1.857 m/s^2, which represents a deceleration of 1.9 m/s^2.

(a) 1 mark: scalar vs vector definition; 1 mark: correct classification of mass and force. (b) 1 mark: 11.5 N. (c) 1 mark: formula a = F / m; 1 mark: 3.3 m/s^2 (or 3.29 m/s^2). (d) 1 mark: stating that friction is the only horizontal / unbalanced force opposing motion. (e) 1 mark: using F = 6.5 N and mass = 3.5 kg; 1 mark: 1.9 m/s^2 (or 1.86 m/s^2).

(a)(i) Internal energy is the sum of the random distribution of kinetic and potential energies of the particles in a system. (ii) Specific latent heat of fusion is the energy required per unit mass to change a substance from solid to liquid without a change in temperature. (b) E = m * c * delta_theta = 0.25 * 2100 * (0 - (-10)) = 0.25 * 2100 * 10 = 5250 J. (c) E = m * L_f = 0.25 * 3.3 x 10^5 = 82500 J. (d) The temperature remains constant at 0 degrees C during melting because the energy supplied is used to break intermolecular bonds.

(a)(i) 1 mark: sum of kinetic and potential energy of particles. (ii) 1 mark: energy to change state of 1 kg from solid to liquid; 1 mark: without temperature change. (b) 1 mark: formula m * c * delta_theta; 1 mark: 5250 J (or 5.25 kJ). (c) 1 mark: formula m * L_f; 1 mark: 82500 J (or 82.5 kJ). (d) 1 mark: remains constant.

(a) Using Snell's law: n = sin i / sin r, so 1.52 = sin 42 / sin r. This gives sin r = sin 42 / 1.52 = 0.6691 / 1.52 = 0.4402. Therefore, r = arcsin(0.4402) = 26.1 degrees (or 26 degrees). (b) Refractive index n = c / v, where c is the speed of light in air and v is the speed of light in glass. So v = c / n = (3.0 x 10^8) / 1.52 = 1.97 x 10^8 m/s. (c) Critical angle is the angle of incidence in an optically denser medium at which the angle of refraction is 90 degrees. It is calculated by sin c = 1 / n = 1 / 1.52 = 0.6579. Therefore, c = arcsin(0.6579) = 41.1 degrees (or 41 degrees).

(a) 1 mark: n = sin i / sin r or sin r = sin 42 / 1.52; 1 mark: 26 degrees (accept 26.1 degrees). (b) 1 mark: formula n = c / v; 1 mark: substitution; 1 mark: 1.97 x 10^8 m/s (accept 2.0 x 10^8 m/s). (c) 1 mark: definition of critical angle; 1 mark: formula sin c = 1 / n; 1 mark: 41 degrees (accept 41.1 degrees).

(a) Properties of all EM waves include: 1. They travel at the same speed in a vacuum (3.0 x 10^8 m/s). 2. They are all transverse waves. 3. They can travel through a vacuum (do not require a medium to propagate). (b)(i) Microwaves are used for satellite television communication. (ii) X-rays are used for bone imaging because they penetrate soft tissue but are absorbed by bone. (iii) Infrared is used in television remote controls. (c) UV radiation exposure can lead to skin damage, premature aging of skin, skin cancer, or eye damage. This risk can be minimized by using high SPF sunscreen, wearing protective sunglasses, or avoiding exposure during peak sunlight hours.

(a) 3 marks: any 3 correct properties (speed of light in vacuum, transverse, can travel in vacuum, transfer energy, reflect/refract). (b) 3 marks: 1 mark for Microwaves, 1 mark for X-rays, 1 mark for Infrared. (c) 1 mark: any valid hazard (sunburn/skin cancer/eye damage); 1 mark: any valid reduction method (sunscreen/shades/clothing).

(a) For parallel resistors: 1 / R_p = 1 / R2 + 1 / R3 = 1 / 6.0 + 1 / 3.0 = 3 / 6.0. Therefore, R_p = 6.0 / 3 = 2.0 ohms. (b) Total resistance is the sum of R1 and the parallel equivalent resistance: R_total = R1 + R_p = 4.0 + 2.0 = 6.0 ohms. (c) Total current I = V / R_total = 12.0 V / 6.0 ohms = 2.0 A. (d) Potential difference across R1: V1 = I * R1 = 2.0 A * 4.0 ohms = 8.0 V. (e) Since R3 (3.0 ohms) has half the resistance of R2 (6.0 ohms), and they are in parallel, the current splits such that twice as much current flows through the smaller resistor. Thus, the current through R3 is twice that of R2.

(a) 1 mark: parallel resistance formula; 1 mark: 2.0 ohms. (b) 1 mark: 6.0 ohms. (c) 1 mark: formula I = V / R; 1 mark: 2.0 A. (d) 1 mark: formula V = I * R; 1 mark: 8.0 V. (e) 1 mark: stating current through R3 is twice/double the current through R2.

(a) Using the transformer equation: V_p / V_s = N_p / N_s, so 240 / V_s = 1200 / 150. Rearranging gives V_s = 240 * (150 / 1200) = 30 V. (b) For a 100% efficient transformer: P_in = P_out, so I_p * V_p = I_s * V_s. Rearranging gives I_p = (I_s * V_s) / V_p = (1.6 * 30) / 240 = 48 / 240 = 0.20 A. (c) Faraday's law states that the magnitude of an induced electromotive force (e.m.f.) is directly proportional to the rate of change of magnetic flux linkage (or the rate at which magnetic field lines are cut). (d) A constant direct current produces a magnetic field of constant strength and direction. Because there is no change in the magnetic field over time, there is no change in magnetic flux linkage in the secondary coil, meaning no e.m.f. is induced.

(a) 1 mark: transformer equation substitution; 1 mark: 30 V. (b) 1 mark: power balance equation; 1 mark: 0.20 A (or 0.2 A). (c) 1 mark: induced e.m.f.; 1 mark: proportional to rate of change of magnetic flux linkage. (d) 1 mark: direct current produces a constant magnetic field; 1 mark: no change in flux means no induced e.m.f.

(a) In a stable main sequence star, the inward force of gravity (which tries to pull the star's matter inward) is balanced by the outward thermal and radiation pressure generated by the nuclear fusion reactions occurring in the core. (b) After the main sequence, a massive star expands to form a Red Supergiant. Eventually, its core collapses rapidly, resulting in a massive explosion called a Supernova. The core remnant left behind is extremely dense, forming either a Neutron Star or, if the mass is high enough, a Black Hole. (c) Redshift is the increase in the wavelength of light from distant galaxies, shifting towards the red end of the spectrum, which indicates that they are moving away from us. Because almost all distant galaxies show redshift, and those further away are moving faster, this shows the universe is expanding. This expansion supports the Big Bang theory, implying that the universe was once concentrated at a single, extremely hot and dense point.

(a) 1 mark: gravitational forces pulling inwards; 1 mark: balanced by outward radiation pressure / thermal pressure. (b) 1 mark: Red Supergiant; 1 mark: Supernova explosion; 1 mark: Neutron Star or Black Hole. (c) 1 mark: defining redshift as an increase in wavelength (or shift to red end) indicating galaxies moving away; 1 mark: shows expanding universe; 1 mark: explains how expansion supports the Big Bang theory.

(a) Specific heat capacity is defined as the thermal energy required per unit mass to increase the temperature of a substance by one degree Celsius (or Kelvin).

(b)(i) Energy is calculated using the formula:
\(E = P \times t\)
Convert minutes to seconds: \(5.0\text{ minutes} = 5.0 \times 60 = 300\text{ s}\)
\(E = 150\text{ W} \times 300\text{ s} = 45000\text{ J}\) (or \(45\text{ kJ}\))

(b)(ii) The temperature change is:
\(\Delta \theta = 74\,^\circ\text{C} - 20\,^\circ\text{C} = 54\,^\circ\text{C}\)

Using the formula:
\(Q = m c \Delta \theta\)
\(c = \frac{Q}{m \Delta \theta}\)
\(c = \frac{45000}{0.80 \times 54} = \frac{45000}{43.2} \approx 1042\text{ J/(kg }^\circ\text{C)}\)

Rounding to two or three significant figures gives \(1040\text{ J/(kg }^\circ\text{C)}\) (or \(1.0 \times 10^3\text{ J/(kg }^\circ\text{C)}\)).

(b)(iii) Some thermal energy from the heater is lost to the surrounding air, or is used to heat the heater itself and the thermometer, rather than raising the temperature of the aluminum block alone.

Part (a):
- Thermal energy per unit mass (or per kg) [1]
- Per unit temperature change (or per °C / K) [1]

Part (b)(i):
- Recall of \(E = Pt\) and conversion of time to seconds (300 s) [1]
- Correct calculation: \(45000\text{ J}\) or \(45\text{ kJ}\) [1]

Part (b)(ii):
- Temperature change calculation: \(\Delta \theta = 54\,^\circ\text{C}\) [1]
- Rearrangement and substitution: \(c = 45000 / (0.80 \times 54)\) [1]
- Final correct value: \(1040\text{ J/(kg }^\circ\text{C)}\) (accept range \(1040\) to \(1042\)) [1]

Part (b)(iii):
- Any valid explanation: Thermal energy lost to the surroundings / heater / thermometer [1]

(a) A step-down transformer consists of a soft iron core wrapped with two separate coils: a primary coil and a secondary coil. Both coils are made of insulated copper wire. For a step-down transformer, the primary coil has more turns than the secondary coil.

(b)(i) Using the transformer turns ratio equation:
\(\frac{V_p}{V_s} = \frac{N_p}{N_s}\)
\(\frac{240}{12} = \frac{1200}{N_s}\)
\(N_s = 1200 \times \frac{12}{240} = 60\text{ turns}\)

(b)(ii) Since the transformer is 100% efficient, power input equals power output:
\(P_{\text{in}} = P_{\text{out}}\)
\(I_p V_p = I_s V_s\)
\(I_p \times 240 = 4.0 \times 12\)
\(I_p = \frac{48}{240} = 0.20\text{ A}\)

(b)(iii) A constant direct current produces a magnetic field that is constant in magnitude and direction. Without a changing magnetic field, there is no change in magnetic flux linkage in the secondary coil, and therefore no electromagnetic induction occurs to induce an electromotive force (e.m.f.) in the secondary coil.

Part (a):
- Soft iron core [1]
- Insulated copper wire/coils [1]
- Primary coil has more turns than secondary coil [1]

Part (b)(i):
- Recall and substitution of transformer equation: \(240 / 12 = 1200 / N_s\) [1]
- Correct evaluation: \(60\) (turns) [1]

Part (b)(ii):
- Recall of power equation: \(I_p V_p = I_s V_s\) [1]
- Correct calculation: \(0.20\text{ A}\) (accept \(0.2\text{ A}\)) [1]

Part (b)(iii):
- Statement that d.c. produces a constant/non-changing magnetic field, which does not induce an e.m.f. [1]