IB Diploma Physics MCQs with answers
Practise IB Diploma Physics (SL / HL) with 232 exam-style MCQs, each with the answer and a short explanation. Every test is marked the moment you finish and shows your score chapter by chapter, so you know what to revise next. It is free and needs no sign-up.
232 questions · 5 chapters
What each chapter covers 5 chapters
The questions follow the syllabus chapter by chapter. You can test the whole subject or one chapter at a time.
- Space, time and motion 47 questionsA.1 Kinematics, A.2 Forces and momentum, A.3 Work, energy and power
- The particulate nature of matter 53 questionsB.1 Thermal energy transfers, B.2 Greenhouse effect, B.3 Gas laws, B.5 Current and circuits
- Wave behaviour 50 questionsC.1 Simple harmonic motion, C.2 Wave model, C.3 Wave phenomena, C.4 Standing waves and resonance, C.5 Doppler effect
- Fields 36 questionsD.1 Gravitational fields, D.2 Electric and magnetic fields, D.3 Motion in electromagnetic fields
- Nuclear and quantum physics 46 questionsE.1 Structure of the atom, E.3 Radioactive decay, E.4 Fission, E.5 Fusion and stars
Sample IB Diploma Physics MCQs with answers 12 questions
12 questions from the test, one or two from each chapter. Try each one, then open the answer.
1. A small steel sphere falls through oil and reaches terminal speed v. A steel sphere of twice the radius is released in the same oil. Assuming Stokes' law applies, what is its terminal speed?
- A
8v
- B
4v
- C
2v
- D
v
Show answer
Answer: B. Weight minus buoyancy is proportional to r³, while drag = 6πηrv is proportional to rv. Equating them gives v ∝ r², so doubling r gives 4v.
2. The solar constant is 1360 W m−2 and the Earth's mean albedo is 0.30. What is the mean solar power absorbed per square metre of the Earth's surface?
- A
340 W m−2
- B
240 W m−2
- C
950 W m−2
- D
100 W m−2
Show answer
Answer: B. Average incident intensity = 1360 ÷ 4 = 340 W m−2; 70% is absorbed: 0.70 × 340 = 238 ≈ 240 W m−2. 950 W m−2 forgets the factor of 4; 100 W m−2 is the reflected part.
3. Glass has a refractive index of 1.5. What is the speed of light in the glass? (c = 3.0 × 108 m s−1)
- A
3.0 × 108 m s−1
- B
4.5 × 108 m s−1
- C
2.0 × 108 m s−1
- D
1.5 × 108 m s−1
Show answer
Answer: C. n = c ÷ v, so v = 3.0 × 108 ÷ 1.5 = 2.0 × 108 m s−1. Light always travels slower in a medium than in a vacuum, so 4.5 × 108 is impossible.
4. In a velocity selector with perpendicular electric and magnetic fields, why does the speed of undeflected particles not depend on their charge?
- A
the electric force depends on the mass as well as the charge
- B
the magnetic force does not depend on charge
- C
only neutral particles pass through undeflected
- D
both the electric force and the magnetic force are proportional to the charge, so it cancels
Show answer
Answer: D. qE = qvB gives v = E/B: q cancels. Particles of any charge or mass with this speed pass straight through.
5. Why is fusion only possible at extremely high temperatures and densities?
- A
nuclei must move fast enough to overcome their electrostatic repulsion and collide often enough
- B
neutrons are needed to slow the nuclei down
- C
nuclei must move slowly so that they can bind together
- D
strong magnetic fields are needed to attract the nuclei together
Show answer
Answer: A. Positive nuclei repel. Only at very high temperatures (about 107 K) are they fast enough to get within range of the strong force, and a high density makes collisions frequent.
6. A skydiver is falling vertically at her terminal speed. Which statement is correct?
- A
her acceleration is equal to g
- B
the drag force is greater than her weight, so she slows down
- C
the drag force is zero because her speed is constant
- D
the drag force equals her weight, so her acceleration is zero
Show answer
Answer: D. At terminal speed the resultant force is zero: upward drag balances weight, so there is no acceleration. Drag is not zero; it is exactly as large as the weight.
7. A battery's terminal p.d. is 12.0 V when no current flows and 11.0 V when it supplies 2.0 A. What is its internal resistance?
- A
5.5 Ω
- B
0.50 Ω
- C
6.0 Ω
- D
2.0 Ω
Show answer
Answer: B. The open-circuit p.d. equals the emf, 12.0 V. The 'lost volts' = 12.0 − 11.0 = 1.0 V = Ir, so r = 1.0 ÷ 2.0 = 0.50 Ω. 5.5 Ω is the external resistance.
8. You can hear someone talking in the next room through an open doorway but cannot see them. What is the main reason?
- A
light cannot reflect off the walls of a room
- B
sound travels faster than light through a doorway
- C
sound wavelengths are similar to the doorway width, so sound diffracts a lot; light wavelengths are far too small
- D
sound is a transverse wave and light is longitudinal
Show answer
Answer: C. Sound has wavelengths of centimetres to metres, comparable to a doorway, so it spreads round the edges. Light's wavelength (about 500 nm) is far too small for noticeable diffraction there.
9. How are the gravitational field lines drawn over a small region near the Earth's surface?
- A
parallel, equally spaced and pointing vertically downwards
- B
circles running round the Earth
- C
radial lines pointing away from the Earth
- D
parallel lines pointing vertically upwards
Show answer
Answer: A. Over a small region the field is uniform, so the lines are parallel and evenly spaced. They point in the direction of the force on a mass: downwards.
10. Which describes the axes of a Hertzsprung–Russell (HR) diagram?
- A
mass on the vertical axis against age on the horizontal axis
- B
luminosity on the vertical axis against surface temperature on the horizontal axis, with temperature increasing to the left
- C
luminosity against surface temperature, with temperature increasing to the right
- D
luminosity on the vertical axis against distance from Earth on the horizontal axis
Show answer
Answer: B. The HR diagram plots luminosity (or absolute magnitude) against surface temperature, and by convention temperature decreases from left to right.
11. An electric motor lifts a 50 kg load through 6.0 m in 12 s while taking 400 W of electrical power. g = 9.8 m s−2. What is its efficiency?
- A
25%
- B
163%
- C
82%
- D
61%
Show answer
Answer: D. Useful power = mgh ÷ t = 50 × 9.8 × 6.0 ÷ 12 = 245 W. Efficiency = 245 ÷ 400 = 0.61 = 61%. 163% is the inverted ratio; efficiency can never exceed 100%.
12. The temperature of a gas rises from 27 °C to 327 °C. By what factor does the mean kinetic energy of its molecules increase?
- A
12
- B
4
- C
√2
- D
2
Show answer
Answer: D. Mean kinetic energy is proportional to absolute temperature: 300 K to 600 K doubles it. Using Celsius (327 ÷ 27 ≈ 12) is the classic trap.
Try 220 more questions
Ways to practise 5 ways
- Quick check. 10 questions drawn fresh each time, about 10 minutes.
- By chapter. 10 questions from one chapter, for the topic you are revising now.
- Full paper. A full-length timed paper across the whole syllabus.
- Practice mode. See the right answer and an explanation after every question, with no clock.
- Exam mode. Timed like the real paper, with no going back.
When you get a question wrong, a short note called "The idea behind this" explains the topic it belongs to, with the rules to remember and a worked example.
Common questions
Is this IB Diploma Physics test free?
Yes. Every test and every explanation is free, and you do not need an account. If you sign in, your results are kept across your devices.
Are these past paper questions?
The 232 MCQs are our own, written to the syllabus in the style of the exam.
How is the test marked?
Instantly. You get your score, the right answer and an explanation for every question, and a list of the topics to work on.
More help with IB Diploma Physics
