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Home · IGCSE 0625 · Nuclear physics · The alpha-scattering experiment · Practice
Extended · Practice questions · The alpha-scattering experiment
Supplement (Extended) content

Observation and conclusion.

Six original Cambridge-style questions on the alpha-scattering experiment: describing it, linking each observation to what it proves, and explaining the evidence for a tiny, dense, positive nucleus.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
What the examiner wants

Always pair the result with the reason.

01
Recall
[3 marks]

Describe the alpha-scattering experiment. State what is fired, what it is fired at, and what is measured.

  • A beam of positive alpha particles is fired. ✓
  • It is fired at a very thin gold foil. ✓
  • The directions in which the alpha particles travel after hitting the foil are measured (the angles they are deflected). ✓
02
Analysis
[1 mark]

Most of the alpha particles passed straight through the foil with little or no deflection. State what this shows about the atom.

  • The atom is mostly empty space. ✓
03
Analysis
[2 marks]

A small number of alpha particles were deflected through large angles. Explain what this tells us, and why the alpha particles were pushed away.

  • There is a concentrated positive charge in the atom (the nucleus). ✓
  • The alpha particle is positive, so it is repelled by the positive nucleus. ✓
04
Analysis
[2 marks]

A very few alpha particles bounced almost straight back towards the source. State the two things this tells us about the nucleus.

  • The nucleus is very small. ✓
  • The nucleus is very dense and contains almost all the mass of the atom. ✓
05
Application
[2 marks]

An alpha particle is fired straight towards the centre of a nucleus. Describe its path and explain what happens.

  • It slows down as it approaches, stops, and is pushed back the way it came (bounces back). ✓
  • The strong repulsion between the positive nucleus and the positive alpha particle turns it around. ✓
06
Application
[2 marks]

Before this experiment, some scientists pictured the atom as positive charge spread evenly through a soft ball. Explain how the bounce-back result shows that this picture must be wrong.

  • Spread-out charge would only bend the fast alpha particles slightly, never turn them back. ✓
  • A bounce-back needs the charge and mass concentrated in a tiny, dense nucleus. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.