A-LevelPhysicsQuantum physics9702/42 · Oct/Nov 2020 · Q76 Marks

Electrons in a beam are travelling at high speed in a vacuum. The electrons are incident on a metal target, causing X-ray radiation to be emitted. The variation with wavelength λ of the intensity I of the emitted X-ray radiation is shown in [Figure 7.1]. Explain why:

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[B1] X-ray photon produced when electron is decelerated
[B1] larger acceleration results in larger photon energy
[B1] continuous range of accelerations so continuous spectrum of wavelengths/frequencies
[B1] electron in (inner shell of) target atom is excited (on collision)
[B1] electron de-excites causing emission of a photon
[B1] discrete energy levels so discrete photon wavelengths

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Topic: Quantum physics, A-Level Physics (syllabus 9702). Structured question, 6 marks.
Source: A-Level Physics, Oct/Nov 2020 Paper 4 Variant 2, question 7.

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