Original open focus revision; complete specification coverage remains unfinished.
1 · Motion graphs and acceleration
velocity · acceleration
ib_physics_hl: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.
ib_physics_hl: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
ib_physics_hl: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.
ib_physics_hl: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 · Energy stores, work and efficiency
power · efficiency
ib_physics_hl: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.
ib_physics_hl: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.
4 · Rigid bodies and rotational dynamics
torque · moment of inertia
ib_physics_hl:rotations:open:1 · 2 marks
What increases torque for the same perpendicular force?
- A larger perpendicular lever arm
- A smaller lever arm
- Only changing the colour of the body
Answer and reasoning · 答案与解析
A larger perpendicular lever arm
- For a rigid body about a fixed axis, net torque equals moment of inertia multiplied by angular acceleration. Rotational kinetic energy depends on angular speed squared. Angular momentum is conserved when net external torque is zero.
ib_physics_hl:rotations:open:2 · 4 marks
A 12 N force acts perpendicularly 0.25 m from the pivot. Find torque.
Answer and reasoning · 答案与解析
3 N m
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Torque has unit N m but is a turning effect, not an energy store. Moment of inertia changes if the same mass moves farther from the axis.
5 · Relativity and measuring events
proper time · inertial frame
ib_physics_hl:relativity:open:1 · 2 marks
Where is proper length measured?
- In the object rest frame
- Only in any fast-moving frame
- In no frame at all
Answer and reasoning · 答案与解析
In the object rest frame
- The Lorentz factor is 1 divided by the square root of 1 minus speed squared over light speed squared. Galilean velocity addition is an approximation for speeds much smaller than light speed.
ib_physics_hl:relativity:open:2 · 4 marks
A proper interval is 8 microseconds and gamma is 1.25. Find the other-frame interval.
Answer and reasoning · 答案与解析
10 μs
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Time dilation is not an instrument fault. Proper length is measured in the object rest frame; a contracted length is measured in a frame where it moves.
6 · Thermal measurements and particle models
specific heat capacity · latent heat
ib_physics_hl: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.
ib_physics_hl: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 · Climate evidence, energy budgets and policy
mitigation · adaptation
ib_physics_hl:ess_climate:open:1 · 2 marks
Which action is adaptation to flood risk?
- Raising vulnerable electrical equipment above expected flood level
- Only measuring global CO2
- Pretending the risk is zero
Answer and reasoning · 答案与解析
Raising vulnerable electrical equipment above expected flood level
- Distinguish mitigation, which addresses drivers, from adaptation, which reduces harm from impacts. A policy assessment needs evidence about effectiveness, cost, equity and uncertainty; one criterion is not the entire decision.
ib_physics_hl:ess_climate:open:2 · 4 marks
Incoming energy is 240 units and reflected energy 72. Find reflected percentage.
Answer and reasoning · 答案与解析
30 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
The greenhouse effect is not the same process as ozone depletion. A carbon footprint estimate depends on its system boundary.
8 · Gas models and absolute temperature
absolute temperature · ideal gas
ib_physics_hl:gases:open:1 · 2 marks
Which scale belongs in a gas-law temperature ratio?
- Celsius
- Kelvin
- Either scale without conversion
Answer and reasoning · 答案与解析
Kelvin
- At fixed amount and volume, pressure is proportional to kelvin temperature. At fixed temperature and amount, pressure is inversely proportional to volume. State which quantities are fixed before choosing a relationship.
ib_physics_hl:gases:open:2 · 4 marks
At fixed volume, pressure is 120 kPa at 300 K. Find pressure at 350 K.
Answer and reasoning · 答案与解析
140 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.
9 · Thermodynamic systems and energy accounts
adiabatic · internal energy
ib_physics_hl:thermodynamics:open:1 · 2 marks
In this convention, what happens during adiabatic compression?
- Internal energy increases
- Heat must enter
- Work done by the gas is positive
Answer and reasoning · 答案与解析
Internal energy increases
- State a sign convention before using the first law. Here change in internal energy equals heat into the system minus work done by the system. Expansion work can reduce internal energy when no heat enters.
ib_physics_hl:thermodynamics:open:2 · 4 marks
A gas gains 500 J of heat and does 200 J work. Find internal-energy change.
Answer and reasoning · 答案与解析
300 J
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Adiabatic does not mean constant temperature. Use the stated sign convention; some courses write work done on the gas with the opposite sign.
10 · Current, potential difference and resistance
current · potential difference
ib_physics_hl: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.
ib_physics_hl: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.
11 · Oscillation, resonance and phase
resonance · damping
ib_physics_hl:oscillations:open:1 · 2 marks
For ideal SHM, where is speed greatest?
- At equilibrium
- At maximum displacement
- At every point equally
Answer and reasoning · 答案与解析
At equilibrium
- Velocity is greatest near equilibrium for ideal SHM, while acceleration magnitude is greatest at extreme displacement. Resonance can occur near the natural frequency under periodic driving, with amplitude limited by damping.
ib_physics_hl:oscillations:open:2 · 4 marks
30 cycles take 45 s. Find period.
Answer and reasoning · 答案与解析
1.5 s
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Not every repeated motion is SHM. A force proportional to displacement but directed away from equilibrium does not produce SHM.
12 · Waves, measurement and refraction
wavelength · frequency
ib_physics_hl: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.
ib_physics_hl: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.
13 · Spectral shifts: a low-speed astronomical estimate
redshift · rest wavelength
ib_physics_hl:light_doppler:open:1 · 2 marks
What does an identified line shifting to a longer wavelength suggest in the stated model?
- Recession along the line of sight
- Light speed increased
- The source frequency must be zero
Answer and reasoning · 答案与解析
Recession along the line of sight
- Compare a identified line with its laboratory rest wavelength. Use z = (observed−rest)/rest, then v approximately cz in the stated low-speed model. Do not apply this approximation without checking the regime or treating a cosmological redshift as a simple exact velocity.
ib_physics_hl:light_doppler:open:2 · 4 marks
A 600 nm rest line is observed at 601.2 nm. Find z=(observed−rest)/rest.
Answer and reasoning · 答案与解析
0.002
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
The approximate shift relation does not show that light travels faster from an approaching source. A single unidentified line cannot safely establish a redshift.
14 · Doppler effect: separate source motion from wave speed
Doppler shift · wavefront
ib_physics_hl:doppler:open:1 · 2 marks
Why is pitch higher in front of an approaching sound source?
- Wavefront spacing is smaller
- Sound speed must become infinite
- The listener creates extra source oscillations
Answer and reasoning · 答案与解析
Wavefront spacing is smaller
- For a source approaching a stationary observer along the line of sight, f observed = f source × v/(v−v source). Recession uses v+v source in the denominator. These are sound-wave models; light requires its appropriate relation.
ib_physics_hl:doppler:open:2 · 4 marks
A 600 Hz source approaches a stationary observer at 20 m/s. Use v = 340 m/s. Find observed frequency.
Answer and reasoning · 答案与解析
637.5 Hz
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A stationary source and moving observer require the observer-motion relation. Do not use the same denominator formula for every arrangement or import a sound formula into relativity.
15 · Gravitational fields and orbital motion
gravitational field · centripetal force
ib_physics_hl:gravitation:open:1 · 2 marks
What direction is the net force in uniform circular motion?
- Toward the centre
- Along the velocity
- Always outward
Answer and reasoning · 答案与解析
Toward the centre
- For a point mass or outside a spherical mass, field strength follows an inverse-square distance dependence. Use distance from the centre, not height above the surface alone.
ib_physics_hl:gravitation:open:2 · 4 marks
Field strength is 18 units at r. Find it at 3r for an inverse-square field.
Answer and reasoning · 答案与解析
2
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Weightlessness in an orbiting spacecraft means apparent weight is small in free fall, not that there is no gravitational field.
16 · Electric fields: force and a positive test charge
electric field strength · test charge
ib_physics_hl:electric_fields:open:1 · 2 marks
What happens to force direction if the test charge changes sign?
- It reverses in the same field
- It always stays along the field
- The field ceases to exist
Answer and reasoning · 答案与解析
It reverses in the same field
- In a uniform field between ideal parallel plates, E = V/d away from edge effects. The force is F = qE, so its direction reverses for a negative charge. Coulomb force between ideal point charges decreases with separation squared.
ib_physics_hl:electric_fields:open:2 · 4 marks
Use E = V/d. Find E for 100 V across 0.025 m.
Answer and reasoning · 答案与解析
4000 V/m
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Field strength is a vector. Potential difference is energy per charge and is not the same quantity. A field-line drawing is a model, not a set of physical threads.
17 · Magnetic forces: turn velocity without increasing speed
magnetic force · momentum
ib_physics_hl:charged_motion:open:1 · 2 marks
What changes under a magnetic force alone in perpendicular circular motion?
- Velocity direction
- Kinetic energy continuously increases
- Charge magnitude
Answer and reasoning · 答案与解析
Velocity direction
- Equate magnetic force with mv²/r to obtain r = mv/(|q|B) for perpendicular motion. A stronger field makes a smaller radius at fixed momentum. Parallel entry gives zero magnetic force in this model.
ib_physics_hl:charged_motion:open:2 · 4 marks
Use r = mv/(|q|B). For m=2×10⁻²⁷ kg, v=2×10⁶ m/s, |q|=1×10⁻¹⁹ C and B=0.20 T, find r.
Answer and reasoning · 答案与解析
0.2 m
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A magnetic force can change momentum direction without doing work. Adding an electric field can change the energy, so conclusions about a magnetic field alone do not cover every combined-field apparatus.
18 · Fields, motors and induction
induction · transformer
ib_physics_hl: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.
ib_physics_hl: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.
19 · Atomic models and line spectra
emission spectrum · energy level
ib_physics_hl:atomic_spectra:open:1 · 2 marks
What produces a higher-frequency emitted photon?
- A larger downward energy difference
- Any transition upward without absorption
- A smaller Planck constant for the same atom
Answer and reasoning · 答案与解析
A larger downward energy difference
- An emitted photon corresponds to a transition to a lower energy level. Absorption requires a compatible energy difference. Rutherford scattering supported a small dense nucleus, but that experiment alone did not establish the complete quantum model.
ib_physics_hl:atomic_spectra:open:2 · 4 marks
Levels are −7.0 and −2.0 eV. Find the energy emitted in the downward transition.
Answer and reasoning · 答案与解析
5 eV
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Negative bound-state energies are relative to a chosen zero; they do not mean a negative photon energy is emitted. A larger downward energy difference gives higher frequency.
20 · Photons and the photoelectric effect
photon · work function
ib_physics_hl:quantum:open:1 · 2 marks
At fixed above-threshold frequency, increasing intensity mainly increases what?
- Photon energy · 光子能量
- The number of emitted electrons per time
- Work function
Answer and reasoning · 答案与解析
The number of emitted electrons per time
- Use photon energy = Planck constant × frequency. Maximum kinetic energy = photon energy - work function. Increasing intensity at fixed frequency increases photon arrival rate, not individual photon energy.
ib_physics_hl:quantum:open:2 · 4 marks
Photon energy is 4.8 eV and work function 2.1 eV. Find maximum kinetic energy.
Answer and reasoning · 答案与解析
2.7 eV
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Electrons do not accumulate many sub-threshold photons in the elementary single-photon model. Do not confuse photon number with photon energy.
21 · Nuclear changes and radiation evidence
half-life · background radiation
ib_physics_hl: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.
ib_physics_hl: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.
22 · Fission: conserve charge and nucleons, account for energy
fission · chain reaction
ib_physics_hl:fission:open:1 · 2 marks
What permits a continuing fission chain reaction?
- Released neutrons initiate further fissions
- Every emitted neutron must escape
- Charge conservation is suspended
Answer and reasoning · 答案与解析
Released neutrons initiate further fissions
- Separate conservation of nucleon number from conservation of total energy. Released neutrons may initiate further fissions, escape or be absorbed. A controlled reactor and an uncontrolled chain reaction have different neutron-management conditions.
ib_physics_hl:fission:open:2 · 4 marks
A U-235 nucleus plus one neutron produces fragments with mass numbers 141 and 92. How many neutrons balance the equation?
Answer and reasoning · 答案与解析
3 neutrons
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Mass number is not a precise mass in kilograms. Balanced integer labels alone do not calculate the released energy. Radioactive decay and neutron-induced fission are not interchangeable descriptions.
23 · Stars, radiation and scale
luminosity · flux
ib_physics_hl:space:open:1 · 2 marks
At fixed luminosity, what happens to flux when distance doubles?
- It halves
- It becomes one quarter
- It doubles
Answer and reasoning · 答案与解析
It becomes one quarter
- For isotropic emission without absorption, flux follows an inverse-square relationship with distance. Observed brightness alone therefore cannot establish luminosity.
ib_physics_hl:space:open:2 · 4 marks
A source gives flux 18 units. Find flux at three times the distance.
Answer and reasoning · 答案与解析
2
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
The Sun is not expected to become a supernova. Redshift can support cosmological expansion; it does not mean every nearby object must move away from every observer.
24 · Uncertainty, gradients and model testing
uncertainty · systematic error
ib_physics_hl:uncertainty:open:1 · 2 marks
Which is most likely a systematic error?
- A balance reads 0.20 g when empty
- Repeated values fluctuate either side of the mean
- Random differences in reaction time
Answer and reasoning · 答案与解析
A balance reads 0.20 g when empty
- For a product or quotient, adding fractional uncertainties is a common maximum-uncertainty approximation. For a difference, add absolute uncertainties. A nonzero intercept can reveal an offset or an incomplete model.
ib_physics_hl:uncertainty:open:2 · 4 marks
A 40 cm reading has an absolute uncertainty of 1 cm. Find percentage uncertainty.
Answer and reasoning · 答案与解析
2.5 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Repeating readings reduces random uncertainty in a mean but does not automatically remove a zero error. Do not quote more decimal places than your measurement can support.