IGCSE · 5 · structured
Nuclear physics · Question 7
Nuclear physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 7
- Topics
- 1
- Answer
- Complete
In the α-particle scattering experiment, a beam of α-particles was directed at a very thin sheet of gold foil in an evacuated container. Most α-particles passed straight through with little or no deviation. A small number were deflected through large angles, and about one in 8000 was deflected through more than 90°.
- (a)
Explain Explain what the observation that most α-particles passed straight through tells us about the structure of the atom.
2 marks - (b)
Explain Explain what the small number of α-particles deflected through more than 90° tells us about the nucleus.
3 marks - (c)
Suggest Suggest why the container had to be evacuated and the gold foil had to be very thin.
2 marks
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(a)
Explain Explain what the observation that most α-particles passed straight through tells us about the structure of the atom.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
most of the atom is empty space
- 2
so most α-particles pass through the foil without coming close to anything that can deflect them
(b)
Explain Explain what the small number of α-particles deflected through more than 90° tells us about the nucleus.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
the positive charge and almost all the mass of the atom are concentrated in a very small volume — the nucleus
- 2
the α-particle is positive, so it is repelled strongly when it passes very close to a nucleus
- 3
such a close approach is rare, which is why so few particles are deflected through large angles
(c)
Suggest Suggest why the container had to be evacuated and the gold foil had to be very thin.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
α-particles are absorbed by only a few centimetres of air, so air in the container would stop them before they reached the foil or the detector
- 2
a thin foil ensures each α-particle is scattered by at most one nucleus, so the deflections can be interpreted
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