2025 Cambridge IGCSE Physics (0625) 模拟试题及答案详解

1. Use the acceleration formula: \(a = \frac{v - u}{t}\)
2. Substitute the given values: \(a = \frac{11.0 - 3.0}{4.0}\)
3. Calculate the final value: \(a = \frac{8.0}{4.0} = 2.0\text{ m/s}^2\).

C1: For stating or using \(a = \frac{v - u}{t}\) or substituting values correctly
A1: For correct final answer with unit: \(2.0\text{ m/s}^2\) (accept \(\text{m/s}^2\) or \(\text{m } s^{-2}\))

1. Determine the volume of the glass: \(V = 62.0 - 32.0 = 30.0\text{ cm}^3\)
2. Use the density formula: \(\rho = \frac{m}{V}\)
3. Substitute the values: \(\rho = \frac{75.0}{30.0} = 2.5\text{ g/cm}^3\).

C1: For calculating volume: \(V = 30.0\text{ cm}^3\)
C1: For recalling/using density formula \(\rho = \frac{m}{V}\)
A1: For correct final answer with unit: \(2.5\text{ g/cm}^3\) (accept \(\text{g/cm}^3\) or \(\text{g cm}^{-3}\))

1. Calculate the work done by the crane: \(W = F \times d = 1500 \times 8.0 = 12\,000\text{ J}\)
2. Use the power formula: \(P = \frac{W}{t}\)
3. Substitute the values: \(P = \frac{12\,000}{6.0} = 2000\text{ W}\) (or \(2.0\text{ kW}\)).

C1: For calculating work done: \(W = F \times d\) or \(12\,000\text{ J}\)
C1: For using power formula: \(P = \frac{W}{t}\) or substituting \(\frac{12\,000}{6.0}\)
A1: For correct final answer with unit: \(2000\text{ W}\) or \(2.0\text{ kW}\)

1. Calculate the weight (force) of the block: \(F = W = m \times g = 15 \times 9.8 = 147\text{ N}\)
2. Use the pressure formula: \(p = \frac{F}{A}\)
3. Substitute the values: \(p = \frac{147}{0.050} = 2940\text{ Pa}\).

C1: For calculating weight: \(W = m \times g = 147\text{ N}\)
C1: For recalling/using pressure formula: \(p = \frac{F}{A}\)
A1: For correct final answer with unit: \(2940\text{ Pa}\) (or \(2900\text{ Pa}\) to 2 s.f., accept \(2.94\text{ kPa}\) or \(\text{N/m}^2\))

1. Convert the time to seconds: \(t = 5.0 \times 60 = 300\text{ s}\)
2. Use the charge formula: \(I = \frac{Q}{t}\)
3. Substitute the values: \(I = \frac{1200}{300} = 4.0\text{ A}\).

C1: For converting time to seconds: \(300\text{ s}\)
C1: For recalling/using current formula: \(I = \frac{Q}{t}\) or substituting \(\frac{1200}{300}\)
A1: For correct final answer with unit: \(4.0\text{ A}\)

1. Use the wave speed equation: \(v = f \times \lambda\)
2. Substitute the given values: \(v = 1500 \times 1.2\)
3. Calculate the speed: \(v = 1800\text{ m/s}\).

C1: For recalling/using wave speed equation: \(v = f \times \lambda\)
A1: For correct final answer with unit: \(1800\text{ m/s}\)

1. Use the circular orbital speed formula: \(v = \frac{2\pi r}{T}\)
2. Substitute the values: \(v = \frac{2 \times \pi \times 8.0 \times 10^6}{4.0 \times 10^3}\)
3. Calculate the speed: \(v = \frac{1.6 \times 10^7 \pi}{4.0 \times 10^3} = 4000\pi \approx 12\,566\text{ m/s}\).
4. Rounding to 2 significant figures gives \(1.3 \times 10^4\text{ m/s}\) (or \(13\,000\text{ m/s}\)).

C1: For stating/using the orbital speed equation: \(v = \frac{2\pi r}{T}\)
C1: For correct substitution: \(v = \frac{2 \times \pi \times 8.0 \times 10^6}{4.0 \times 10^3}\)
A1: For correct final answer: \(1.3 \times 10^4\text{ m/s}\) or \(13\,000\text{ m/s}\) (accept \(12\,500\) to \(12\,600\))

1. Find the number of half-lives that have elapsed:
- \(2400 \rightarrow 1200\) (1 half-life)
- \(1200 \rightarrow 600\) (2 half-lives)
- \(600 \rightarrow 300\) (3 half-lives)
2. The total time elapsed is \(18\text{ hours}\) for 3 half-lives.
3. Calculate the duration of one half-life: \(t_{1/2} = \frac{18\text{ hours}}{3} = 6.0\text{ hours}\).

C1: For determining that 3 half-lives have elapsed
C1: For setting up the relation: \(3 \times t_{1/2} = 18\text{ hours}\)
A1: For correct final answer with unit: \(6.0\text{ hours}\)

Using the formula F = ma, we can rearrange to find acceleration: a = F / m. Substituting the given values: a = 3.2 N / 0.80 kg = 4.0 m/s^2.

C1: for quoting the formula F = ma or rearranged a = F/m. A1: for the correct final answer with appropriate unit: 4.0 m/s^2 (accept 4 m/s^2).

Using the formula p = mv, we substitute the mass and speed: p = 2.0 kg * 3.5 m/s = 7.0 kg m/s.

C1: for quoting the formula p = mv or showing substitution 2.0 * 3.5. A1: for the correct final answer with appropriate unit: 7.0 kg m/s (accept 7 kg m/s or 7 N s).

Using the formula p = F / A, we substitute the force (weight) and area: p = 150 N / 0.25 m^2 = 600 Pa.

C1: for quoting the formula p = F/A or showing substitution 150 / 0.25. A1: for the correct final answer with appropriate unit: 600 Pa (accept 600 N/m^2).

Using the formula P = W / t, we substitute the work and time: P = 1200 J / 15 s = 80 W.

C1: for quoting the formula P = W/t or showing substitution 1200 / 15. A1: for the correct final answer with appropriate unit: 80 W (accept 80 J/s).

Using Ohm's law, R = V / I. Substituting the potential difference and current: R = 12 V / 0.75 A = 16 ohms.

C1: for quoting the formula R = V/I or V = IR. A1: for the correct final answer with appropriate unit: 16 Δ (or 16 ohms).

Using the formula rho = m / V, we substitute the mass and volume: rho = 450 g / 50 cm^3 = 9.0 g/cm^3.

C1: for quoting the formula rho = m/V or showing substitution 450 / 50. A1: for the correct final answer with appropriate unit: 9.0 g/cm^3 (accept 9 g/cm^3 or 9000 kg/m^3 if conversions are correctly shown).

Using the wave equation v = f * lambda, we substitute frequency and wavelength: v = 5.0 Hz * 0.20 m = 1.0 m/s.

C1: for quoting the formula v = f * lambda or showing substitution 5.0 * 0.20. A1: for the correct final answer with appropriate unit: 1.0 m/s (accept 1 m/s).

A vacuum contains no particles (is empty space), which completely prevents thermal energy transfer by conduction and convection, as both processes require a material medium. Although dry air is a poor conductor, it still contains molecules that allow some conduction and can support the formation of convection currents within the gap.

- [1 mark] State that a vacuum contains no particles (empty space), so conduction and convection cannot occur.
- [1 mark] State that dry air contains particles, which still allows some conduction and/or the formation of convection currents.

When light travels from a more optically dense medium (water) to a less optically dense medium (air), and the angle of incidence exceeds the critical angle, the light cannot refract. Instead, it undergoes total internal reflection and is entirely reflected back into the water.

- [1 mark] State that total internal reflection occurs (the light is reflected back into the water).
- [1 mark] Explain that this is because the light is travelling in a more dense medium towards a less dense medium and the angle of incidence is greater than the critical angle.

The airbag increases the time interval \( t \) over which the passenger's momentum changes to zero. Since force is equal to the rate of change of momentum, \( F = \frac{\Delta p}{t} \), a larger value of \( t \) results in a much smaller average force acting on the passenger, reducing the risk of injury.

- [1 mark] State that the airbag increases the time duration of the collision / impact.
- [1 mark] Explain that this reduces the rate of change of momentum, resulting in a smaller force acting on the passenger (or mention the relationship \( F = \frac{\Delta p}{t} \)).

Snowshoes have a much larger surface area in contact with the snow compared to ordinary boots. According to the formula for pressure, \( P = \frac{F}{A} \), spreading the person's weight (force \( F \)) over a larger area \( A \) results in a much lower pressure \( P \) on the snow, preventing them from sinking.

- [1 mark] State that the snowshoes have a larger surface area than ordinary boots.
- [1 mark] Explain that the larger area reduces the pressure exerted on the snow because the force (weight) is distributed over a larger area (or mention \( P = \frac{F}{A} \)).

The soft iron keepers become magnetised by induction from the permanent magnets. This creates a continuous, closed magnetic loop for the magnetic field lines. By keeping the magnetic loops closed, the magnetic domains within the permanent bar magnets remain aligned over time, preventing demagnetisation.

- [1 mark] State that the iron keepers become magnetised by induction, forming closed loops of magnetic field lines.
- [1 mark] Explain that this keeps the magnetic domains aligned and prevents demagnetisation of the permanent magnets.

Alpha particles have a relatively large mass and a positive charge of \( +2e \), which makes them highly ionising. They interact strongly and frequently with air molecules, losing their kinetic energy rapidly over a short distance. In contrast, gamma rays are electromagnetic waves with no charge and no mass, making them weakly ionising so they interact rarely and travel much further before losing their energy.

- [1 mark] State that alpha particles are highly ionising (or have a double positive charge / large mass), so they collide frequently with air molecules and lose energy quickly.
- [1 mark] State that gamma rays are weakly ionising (or have no charge / no mass), so they interact rarely and have a much greater range.

As the distance between the planet and the Sun increases, the gravitational force of attraction holding the planet in its orbit decreases. This weaker force results in a smaller centripetal acceleration, meaning the planet's orbital speed decreases. Alternatively, as the planet moves further away, its kinetic energy is converted into gravitational potential energy, resulting in a slower speed.

- [1 mark] State that the orbital speed decreases.
- [1 mark] Explain that the gravitational force of attraction from the Sun becomes weaker at greater distances (or explain in terms of kinetic energy converting to gravitational potential energy).

Redshift is the increase in the observed wavelength (or decrease in frequency) of light emitted by distant galaxies as they move away from the observer. This observation indicates that distant galaxies are moving away from us, and the fact that almost all distant galaxies show redshift indicates that the Universe is expanding.

- [1 mark] Define redshift as an increase in the observed wavelength of light (or shift of light towards the red end of the spectrum).
- [1 mark] Explain that this indicates galaxies are moving away from us, which shows that the Universe is expanding.

When the water at the bottom of the beaker is heated, it expands and its volume increases. This expansion causes its density to decrease. The less dense warm water rises towards the top. At the same time, the cooler, denser water at the top sinks to the bottom to take its place. This continuous cycle forms a convection current that heats all the water in the beaker.

1. [1] Heating causes the water to expand and decrease in density.
2. [1] The less dense warm water rises and the cooler, denser water sinks, forming a convection current.

Since the light ray is travelling in a more dense medium (glass) towards a less dense medium (air) and the angle of incidence is greater than the critical angle, total internal reflection occurs. No light is refracted out of the glass block. Instead, all of the light is reflected back into the glass block, obeying the law of reflection where the angle of reflection equals the angle of incidence.

1. [1] Total internal reflection occurs / no light refracts out of the block.
2. [1] All the light reflects back into the glass with the angle of reflection equal to the angle of incidence.

Sound waves are longitudinal mechanical waves that propagate through the vibration of particles. Because space is a vacuum, there are no particles, so sound cannot travel to the astronaut's ears. On the other hand, light is an electromagnetic wave that consists of oscillating electric and magnetic fields, which does not require any material medium to travel and can easily propagate through a vacuum.

1. [1] Sound is a mechanical wave / requires a material medium to travel (which is absent in the vacuum of space).
2. [1] Light is an electromagnetic wave / does not require a medium to travel (and can propagate through a vacuum).

Alpha particles are positively charged helium nuclei and are attracted towards the negatively charged plate. Beta particles are negatively charged electrons and are attracted towards the positively charged plate, so they deflect in opposite directions. Additionally, beta particles are deflected much more than alpha particles because their mass is extremely small compared to the mass of alpha particles, resulting in a much larger acceleration for a given force.

1. [1] Deflection is in opposite directions because alpha is positively charged (deflected towards negative plate) and beta is negatively charged (deflected towards positive plate).
2. [1] Beta particles deflect much more because they have a much smaller mass than alpha particles.

The electromotive force (e.m.f.) is defined as the work done by the source (or energy transferred from other forms to electrical energy) per unit charge in driving charge around a complete circuit.

1 mark for: work done per unit charge (or energy transferred per unit charge). 1 mark for: around a complete circuit.

When drawing magnetic field lines, the lines must never cross each other, and they must show the direction of the magnetic field from the North pole to the South pole.

1 mark for: field lines do not cross/intersect. 1 mark for: direction is from North to South (indicated by arrows).

When air is heated, it expands and its volume increases, causing its density to decrease. The surrounding cooler, denser air sinks and pushes the less dense warm air upwards, causing it to rise.

1 mark for: heated air expands and its density decreases. 1 mark for: less dense warm air is pushed up by the cooler denser air.

The sound travels to the wall and back, so the total distance is 2 * 85 m = 170 m. Using the formula time = distance / speed, we get time = 170 / 340 = 0.50 s.

1 mark for: using total distance 170 m or formula t = 2d/v. 1 mark for: 0.50 s (with unit).

On a speed-time graph, the acceleration is given by the gradient (or slope) of the line. The distance travelled by the object is represented by the area under the line.

1 mark for: acceleration is the gradient/slope. 1 mark for: distance is the area under the graph.

An alpha particle has a proton number of 2 and a nucleon number of 4. Emitting an alpha particle decreases the proton number of the nucleus by 2 (88 - 2 = 86) and the nucleon number by 4 (226 - 4 = 222).

1 mark for: proton number is 86. 1 mark for: nucleon number is 222.

According to the law of reflection, the angle of reflection is equal to the angle of incidence, so it is 40 degrees. Reflection is a boundary phenomenon where light stays in the same medium, so the speed of light remains unchanged.

1 mark for: 40 degrees. 1 mark for: speed remains unchanged/constant.

The daily cycle of day and night is caused by the Earth rotating on its own axis once every 24 hours. The yearly cycle of seasons is caused by the tilt of the Earth's axis of rotation relative to its orbital plane as it travels around the Sun.

1 mark for: rotation of the Earth (on its axis) causing day and night. 1 mark for: tilt of the Earth's axis / orbit around the Sun causing seasons.

Since the angle of incidence (\(48^\circ\)) is greater than the critical angle (\(42^\circ\)) and the light is travelling from a more optically dense medium (glass) to a less optically dense medium (air), the ray of light cannot refract out into the air. Instead, it undergoes total internal reflection, reflecting back into the glass block with an angle of reflection equal to the angle of incidence (\(48^\circ\)).

[1] State that the ray is reflected back into the glass / undergoes reflection (at an angle of \(48^\circ\)). [1] Identify the phenomenon as total internal reflection.

The magnetic field lines always point from the North pole to the South pole outside a magnet. The density or spacing of the magnetic field lines represents the strength of the field: where the lines are closer together (such as near the poles), the magnetic field is strongest.

[1] Direction of field lines: from North (N) to South (S). [1] Spacing: closer/denser lines represent a stronger magnetic field (or vice versa).