Original open focus revision; complete specification coverage remains unfinished.
1 · Motion graphs and acceleration
velocity · acceleration
edexcel_igcse_physics:motion:open:1 · 2 marks
What does area under a velocity-time graph represent?
- Displacement · 置换反应
- Acceleration · 加速度
- Mass · 质量
Answer and reasoning · 答案与解析
Displacement · 置换反应
- The gradient of a displacement-time graph is velocity. The area under a velocity-time graph gives displacement. A constant-acceleration formula is valid only when its assumption is justified.
edexcel_igcse_physics:motion:open:2 · 4 marks
Velocity changes from 3 to 15 metres per second in 6 s. Find acceleration.
Answer and reasoning · 答案与解析
2 m/s²
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Negative velocity indicates direction under the chosen sign convention; it does not necessarily mean slowing down.
2 · Forces, momentum and safe stopping
momentum · resultant force
edexcel_igcse_physics:forces:open:1 · 2 marks
For fixed momentum change, which reduces average stopping force?
- Longer stopping time
- Shorter stopping time
- Ignoring external force
Answer and reasoning · 答案与解析
Longer stopping time
- Impulse equals momentum change. Increasing stopping time for the same momentum change reduces average force. Identify external forces before applying momentum conservation.
edexcel_igcse_physics:forces:open:2 · 4 marks
A 2 kg trolley travels at 3 metres per second. Find its momentum.
Answer and reasoning · 答案与解析
6 kg·m/s
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Balanced forces do not require the object to be at rest. Mass and weight have different units and meanings.
3 · Current, potential difference and resistance
current · potential difference
edexcel_igcse_physics:circuits:open:1 · 2 marks
How is a voltmeter connected to measure voltage across a resistor?
- In parallel with the resistor
- In series only
- Across the ammeter only
Answer and reasoning · 答案与解析
In parallel with the resistor
- Current is the same through components in series. Potential differences add around the series path. In parallel, branches share the same potential difference, while branch currents sum at a junction.
edexcel_igcse_physics:circuits:open:2 · 4 marks
A component has 12 V across it and carries 0.40 A. Find resistance.
Answer and reasoning · 答案与解析
30 Ω
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Current is not used up by a lamp. A filament heats up, so its resistance need not remain constant as voltage changes.
4 · Waves, measurement and refraction
wavelength · frequency
edexcel_igcse_physics:waves:open:1 · 2 marks
When a wave enters a slower medium, what stays constant?
- Frequency · 频率
- Wavelength · 波长
- Speed · 速度
Answer and reasoning · 答案与解析
Frequency · 频率
- At a boundary, frequency stays fixed by the source. A change of speed changes wavelength. Refraction follows from speed differences; angles are measured from the normal.
edexcel_igcse_physics:waves:open:2 · 4 marks
Frequency is 8 Hz and wavelength is 0.25 m. Find wave speed.
Answer and reasoning · 答案与解析
2 m/s
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
The wave frequency does not change simply because the medium changes. A longitudinal wave has oscillations parallel to propagation.
5 · Energy stores, work and efficiency
power · efficiency
edexcel_igcse_physics:mechanical_energy:open:1 · 2 marks
What happens to kinetic energy when speed doubles at fixed mass?
- It doubles
- It quadruples
- It stays constant
Answer and reasoning · 答案与解析
It quadruples
- Define the system and useful output before calculating efficiency. Doubling speed quadruples kinetic energy at constant mass. Power describes transfer per time, not total energy.
edexcel_igcse_physics:mechanical_energy:open:2 · 4 marks
A device receives 250 J and gives 150 J useful output. Find efficiency as a percentage.
Answer and reasoning · 答案与解析
60 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Efficiency cannot exceed 100% for a properly defined energy balance. Energy dissipated by heating is still conserved.
6 · Thermal measurements and particle models
specific heat capacity · latent heat
edexcel_igcse_physics:thermal:open:1 · 2 marks
Why can temperature stay constant while a pure substance melts?
- No energy enters
- Energy changes particle arrangement
- The thermometer must be broken
Answer and reasoning · 答案与解析
Energy changes particle arrangement
- Temperature relates to particle motion in a model; internal energy includes kinetic and potential contributions. During a change of state, energy can change particle arrangements rather than temperature.
edexcel_igcse_physics:thermal:open:2 · 4 marks
A 2 kg sample with c=500 J per kilogram per degree warms by 3 °C. Find energy gain.
Answer and reasoning · 答案与解析
3000 J
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A flat section of a heating curve can show a phase change, not absence of energy transfer. Do not substitute temperature for a temperature difference in E = mcΔT.
7 · Gas models and absolute temperature
absolute temperature · ideal gas
edexcel_igcse_physics:gases:open:1 · 2 marks
For a fixed amount of gas at constant temperature, halving volume does what to pressure?
- Halves it
- Doubles it
- Leaves it unchanged
Answer and reasoning · 答案与解析
Doubles it
- State which quantities stay fixed. A pressure-volume relation requires consistent units and a fixed temperature. The kelvin-based temperature ratio is an extension only where the course explicitly specifies it.
edexcel_igcse_physics:gases:open:2 · 4 marks
At fixed temperature, pressure is 120 kPa at volume 50 cubic centimetres. Find pressure at volume 30 cubic centimetres.
Answer and reasoning · 答案与解析
200 kPa
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
An ideal gas is a model with conditions of validity. Celsius zero is not zero molecular motion, and internal energy is not determined by pressure alone.
8 · Fields, motors and induction
induction · transformer
edexcel_igcse_physics:fields:open:1 · 2 marks
Which gives a continuing emf in a coil?
- A constant unchanging flux
- A changing flux linkage
- A nearby stationary magnet in every situation
Answer and reasoning · 答案与解析
A changing flux linkage
- Changing field strength, coil area, orientation or relative motion can change flux linkage. Lenz law describes an induced effect opposing the change producing it, consistent with energy conservation.
edexcel_igcse_physics:fields:open:2 · 4 marks
An ideal transformer has Np=400, Ns=100 and Vp=20 V. Find Vs.
Answer and reasoning · 答案与解析
5 V
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A transformer needs changing magnetic flux; a steady DC input does not provide continuous transformer action. Magnetic field direction is not automatically the direction of force.
9 · Nuclear changes and radiation evidence
half-life · background radiation
edexcel_igcse_physics:nuclear:open:1 · 2 marks
Which count should be used for source activity?
- Raw source-plus-background only
- Measured count minus background over equal times
- The largest repeated count only
Answer and reasoning · 答案与解析
Measured count minus background over equal times
- Subtract background counts measured over the same time interval. Distinguish irradiation from contamination. Shielding, distance and reduced exposure time can reduce risk under a school-controlled procedure.
edexcel_igcse_physics:nuclear:open:2 · 4 marks
An initial source count is 160 per minute. Find it after three half-lives.
Answer and reasoning · 答案与解析
20 counts/min
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
An irradiated object is not automatically radioactive. A half-life does not predict the exact decay time of one nucleus.
10 · Stellar evolution: initial mass changes the route
main sequence · white dwarf
edexcel_igcse_physics:stellar_evolution:open:1 · 2 marks
Which final route is appropriate for the Sun in the school model?
- Red giant followed by white dwarf
- Every star becomes a black hole
- A supernova is required for every star
Answer and reasoning · 答案与解析
Red giant followed by white dwarf
- Read a life-cycle diagram as a model of stages and conditions, not a timed film of one star. The Sun is expected to follow the lower-mass route. Fusion combines light nuclei; it differs from fission of a heavy nucleus.
edexcel_igcse_physics:stellar_evolution:open:2 · 4 marks
6 of 30 stars in an illustrative sample are in a chosen stage. Calculate the percentage.
Answer and reasoning · 答案与解析
20 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
The Sun is not expected to become a supernova. A diagram does not establish that every massive star makes the same remnant, nor that all stages last the same time.