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Question 20N.2.HL.TZ0.b(iii)

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Date November 2020 Marks available [Maximum mark: 2] Reference code 20N.2.HL.TZ0.b(iii)
Level HL Paper 2 Time zone TZ0
Command term Outline Question number b(iii) Adapted from N/A
b(iii).
[Maximum mark: 2]
20N.2.HL.TZ0.b(iii)

The de Broglie wavelength λ of a particle accelerated close to the speed of light is approximately

λ≈hcE

where E is the energy of the particle.
A beam of electrons of energy 4.2×108 eV is produced in an accelerator.

The electron beam is used to study the nuclear radius of carbon-12. The beam is directed from the left at a thin sample of carbon-12. A detector is placed at an angle θ relative to the direction of the incident beam.

The graph shows the variation of the intensity of electrons with θ. There is a minimum of intensity for θ=θ0.

Outline why electrons with energy of approximately 107 eV would be unsuitable for the investigation of nuclear radii.

[2]

Markscheme

the de Broglie wavelength of electrons is «much» longer than the size of a nucleus ✓


hence electrons would not undergo diffraction
OR
no diffraction pattern would be observed ✓

Examiners report

Candidates generally scored poorly on this question. There was confusion between this experiment and another diffraction one, so often the new wavelength was compared to the spacing between atoms. Also, in line with answers to b(i) there were suggestions that the electrons did not have sufficient energy to reach the nucleus or would be deflected by too great an angle to be seen.

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