Nuclear Physics: Paper 2 Answering Guide (Form 5 SPM Physics)

Paper 2 at a glance

• Section B: 2 items worth 20 marks, answer one

"Define" items from this chapter

One precise sentence each; the unit is part of the definition where there is one.

• Isotope, Atoms of the same element that have the same number of protons but different numbers of neutrons.
• Radioactivity, The spontaneous emission of radiation (alpha, beta or gamma) from the unstable nuclei of certain atoms.
• Alpha particle, A particle made of two protons and two neutrons (a helium nucleus) emitted by some radioactive nuclei; it has a positive charge and low penetrating power.
• Beta particle, A high-speed electron emitted from the nucleus when a neutron changes into a proton; it has a negative charge and moderate penetrating power.
• Gamma ray, A high-frequency electromagnetic wave emitted by an unstable nucleus; it has no charge and very high penetrating power.
• Radioactive decay, The random process by which an unstable nucleus loses energy by emitting radiation and changes into a more stable nucleus.

"Explain" items from this chapter

Give the physics reason, not a description. Model answers in one breath:

• What half-life means, Half-life is the time for half of the radioactive nuclei in a sample to decay. It stays the same no matter how much you start with, because decay is a fixed-chance process for each nucleus.
• Why nuclear reactions release so much energy, In a nuclear reaction the products have slightly less mass than the starting materials. This lost mass is converted into a large amount of energy, following E = mc squared.
• Why radioactive decay is random, You cannot predict which nucleus will decay next or when, and nothing outside can trigger it. Decay is spontaneous and random, yet a huge number of nuclei together follow a steady, predictable rate.

"Calculate" items from this chapter

Formula, substitution with units, answer with unit, and the trap examiners set for each one.

• E = mc², Mass–energy equivalence, E = energy released (J); m = mass defect (kg); c = speed of light (m s⁻¹) · Square c (c² = 9.0 × 10¹⁶). m is the mass defect in kilograms, convert from grams or atomic mass units first.
• N = N₀ (½)ⁿ, Radioactive decay (half-life), N = quantity remaining (no unit) (); N₀ = initial quantity (no unit) (); t = elapsed time (s); T½ = half-life (s); n = number of half-lives (= t / T½) () · First find how many half-lives (t / T½); each one halves the amount. t and T½ must use the same time unit.

Other command words

• Suggest / Modify (Section C), one modification, one reason, tied to a named physics principle; repeat for each aspect the question lists.
• Describe, say what happens, in order, with the observable evidence; keep "why" for an explain mark.

Where the marks are in this chapter

The 2 content standards of Nuclear Physics can each be asked as a definition, an explanation, a calculation or a diagram. We do not predict which will appear, prepare all of them.

• 6.1 Radioactive Decay
• 6.2 Nuclear Energy

A three-step answer routine

1. Count the marks: one idea per mark, so a 3-mark explain needs three physics statements.
2. Name the quantity and its symbol before you use it.
3. Re-read the stem for a hidden condition (constant temperature, uniform acceleration, smooth surface).

More Nuclear Physics resources

• Chapter overview: Nuclear Physics
• Revision Notes
• Common Mistakes
• Practice Questions
• Paper 3 Guide
• Key Terms
• Calculation practice sets

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)