Physics · AQA 7408 · Option D · Topic 3.12

Turning points in physics

Option: the experiments that changed physics, from the electron and the nature of light to special relativity.

  • 15 sub-topics
  • Taught in Year 13
  • 99 practice questions
  • 15 animated lessons
Practice questions (99) Lessons Worksheets All AQA Physics topics

What the specification says

Every sub-topic AQA can examine in this topic, with its reference number from the official specification. The Y12 and Y13 tags show when each sub-topic is usually taught.

  1. 3.12.1 The discovery of the electron
  2. 3.12.1.1Cathode raysY13
  3. 3.12.1.2Thermionic emission of electronsY13
  4. 3.12.1.3Specific charge of the electronY13
  5. 3.12.1.4Principle of Millikan's determination of the electronic charge, eY13
  6. 3.12.2 Wave-particle duality
  7. 3.12.2.1Newton's corpuscular theory of lightY13
  8. 3.12.2.2Significance of Young's double slits experimentY13
  9. 3.12.2.3Electromagnetic wavesY13
  10. 3.12.2.4The discovery of photoelectricityY13
  11. 3.12.2.5Wave–particle dualityY13
  12. 3.12.2.6Electron microscopesY13
  13. 3.12.3 Special relativity
  14. 3.12.3.1The Michelson-Morley experimentY13
  15. 3.12.3.2Einstein's theory of special relativityY13
  16. 3.12.3.3Time dilationY13
  17. 3.12.3.4Length contractionY13
  18. 3.12.3.5Mass and energyY13

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Turning points in physics

Not needed for Year 12Easy

Cathode rays · Year 13 · 3 marks

Cathode rays are produced in a discharge tube.
  1. (a)
    State what cathode rays are.
    (1)
  2. (b)
    Explain why the gas in a discharge tube glows.
    (2)
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Part (a)1 mark

  1. Beams of electrons.

Part (b)2 marks

  1. Electrons collide with gas atoms and excite them;
  2. the atoms emit photons as they de-excite.

Total3

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Nuclear and particle physics

Not needed for Year 12Medium

Accelerating electrons · Year 13 · 4 marks

Electrons are released from a heated filament and accelerated through a p.d. of 4500 V.
  1. (a)
    Explain why electrons are released from the heated filament.
    (1)
  2. (b)
    Calculate the kinetic energy gained, and the final speed of the electrons.
    (3)

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Part (a)1 mark

  1. Thermionic emission: some free electrons gain enough energy to escape the metal surface.

Part (b)3 marks

  1. Ek=eVE_k = eV
  2. EkE_k=7.20×10−16 J{}= 7.20 \times 10^{-16}\ \mathrm{J}
  3. vv=3.98×107 m s−1{}= 3.98 \times 10^{7}\ \mathrm{m\,s^{-1}}

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Nuclear and particle physics

Not needed for Year 12Hard

Relativistic time dilation · Year 13 · 4 marks

Muons have a mean lifetime of 2.2 μs in their rest frame. Muons are produced high in the atmosphere moving at 0.99c.
  1. (a)
    Calculate the mean lifetime measured by an observer on the ground.
    (2)
  2. (b)
    Calculate the mean distance travelled in the ground frame, and explain why many muons reach the ground.
    (2)

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Part (a)2 marks

  1. t=t01−v2/c2t = \frac{t_0}{\sqrt{1 - v^2/c^2}}
  2. tt=1.56×10−5 s{}= 1.56 \times 10^{-5}\ \mathrm{s}

Part (b)2 marks

  1. d=4632 md = 4632\ \mathrm{m}
  2. Without time dilation they would travel only about 653 m on average.

Total4

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  • B
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