The Physics Question Bank

Level 3 (5–6 marks): a clear, logical account of both models, with the scattering evidence correctly linked to the conclusions, and the contributions of Bohr and Chadwick.
Level 2 (3–4 marks): both models described, with some evidence from the scattering experiment linked to the nuclear model.
Level 1 (1–2 marks): simple statements about one model or the experiment.
0 marks: no relevant content.

Indicative content:
• plum pudding: a ball of positive charge with electrons embedded in it
• alpha particles were fired at thin gold foil
• most passed straight through, so most of the atom is empty space
• some were deflected, so the centre is positively charged
• a very few bounced back, so the mass is concentrated in a tiny nucleus
• Bohr: electrons orbit the nucleus at specific distances (energy levels)
• Chadwick: the nucleus also contains neutrons
• the model changed because new evidence could not be explained by the old model

mass number 14 (1)
atomic number 7 (1)

a neutron changes into a proton and an electron, and the electron is emitted (1)

²¹⁰₈₄Po → ²⁰⁶₈₂Pb + ⁴₂He
correct alpha particle symbol (1)
correct mass number and atomic number of lead (1)

gamma rays are electromagnetic waves, with no mass and no charge (1)

it moves to a higher energy level / further from the nucleus (1)
allow: it may leave the atom, forming an ion

500 counts per minute (1)

12 days = 4 half-lives (1)
1200 → 600 → 300 → 150 → 75 Bq (1)

1/16 (1) – allow 0.0625 or 6.25%

radioactive decay is random – half-life only describes what happens to a large number of nuclei (1)

outside the body, alpha is stopped by the outer layer of skin / a few cm of air (1)
inside the body, it is close to living cells / organs (1)
alpha is highly ionising, so it causes a lot of damage to cells in a small area (1)

it can damage DNA / cause mutations in cells (1)

so other scientists can check the findings / repeat the work, making the conclusions more reliable (1)