About Atomic physics in O Level Physics
Atomic physics is one of the 14 main topics in our O Level Physics (Cambridge (CAIE) 5054) question bank, and about 2% of its real questions come from it. Tayyari Karo has 15 real questions on this topic from 2022 to 2025, from Paper 1, Paper 2; 10 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 7 easy, 6 medium, 2 hard.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 6 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
Oct/Nov 2025 · Paper 1 · Atomic physics
Four statements about an atom are listed:
1 The atom has a nucleus surrounded by positively charged electrons.
2 Most of the atom is empty space.
3 The nucleus is positively charged.
4 The nucleus is very large compared with the rest of the atom.
Which statements are correct?
- 1 and 2
- 1 and 4
- 2 and 3
- 3 and 4
Show answer and explanation
Answer: C. 2 and 3
Electrons are negatively charged (not positive), so statement 1 is wrong; the nucleus is extremely small compared with the whole atom (not large), so statement 4 is wrong. Most of the atom is empty space (2) and the nucleus is positively charged (3) are both correct.
Oct/Nov 2025 · Paper 1 · Atomic physics
A smoke alarm contains a radioactive source, S. The useful emissions from S are blocked by a few centimetres of air.
What is the useful radioactive radiation emitted by S?
- alpha and gamma
- alpha only
- beta and gamma
- beta only
Show answer and explanation
Answer: B. alpha only
Alpha particles have a very short range and are stopped by only a few centimetres of air, unlike beta and gamma radiation which travel much further; this short range is exactly what allows a smoke alarm to detect smoke blocking the source.
May/June 2024 · Paper 1 · Atomic physics
Nuclear fusion is one source of energy. What is nuclear fusion?
- the decay of a radioactive nucleus
- the joining together of two nuclei to make a larger nucleus
- the melting of an unstable nucleus
- the splitting of a nucleus into two lighter nuclei
Show answer and explanation
Answer: B. the joining together of two nuclei to make a larger nucleus
Nuclear fusion is the joining of two smaller nuclei to form a single larger nucleus, releasing energy.
Oct/Nov 2024 · Paper 1 · Atomic physics
Which row identifies the positive and negative particles in the atom?
- positive: proton, negative: electron
- positive: electron, negative: proton
- positive: proton, negative: neutron
- positive: neutron, negative: proton
Show answer and explanation
Answer: A. positive: proton, negative: electron
The proton is the positively charged particle and the electron is the negatively charged particle in an atom; the neutron carries no charge.
May/June 2023 · Paper 1 · Atomic physics
The results of a scattering experiment show that a very small nucleus contains most of the matter in an atom.
What is scattered in this experiment?
- alpha-particles
- beta-particles
- gamma radiation
- gold nuclei
Show answer and explanation
Answer: A. alpha-particles
In the Geiger–Marsden experiment a beam of alpha-particles was fired at thin gold foil, and the few that bounced back revealed the tiny massive nucleus.
May/June 2023 · Paper 1 · Atomic physics
Atoms P and Q are isotopes of the same element.
How does the composition of an atom of P compare with the composition of an atom of Q?
- different number of protons, different number of neutrons
- different number of protons, same number of neutrons
- same number of protons, different number of neutrons
- same number of protons, same number of neutrons
Show answer and explanation
Answer: C. same number of protons, different number of neutrons
Isotopes are atoms of the same element, so the proton number must be the same, and they differ only in the number of neutrons.
