The uppermost energy bands in a solid are known as the valence band (VB), the forbidden band (FB) and the conduction band (CB). A copper wire is at room temperature. The structure of a copper crystal is to be examined using electron diffraction. Electrons, having been accelerated from rest through a potential difference V, are incident on the crystal. The de Broglie wavelength λ of the electrons is 2.6 × 10⁻¹¹ m.

Q: What topic does this question test?

This question tests Quantum physics in A-Level Physics (syllabus code 9702). It is worth 8 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Physics May/June 2020 examination, Paper 4 Variant 2 (9702_s20_qp_42.pdf).

Question

The uppermost energy bands in a solid are known as the valence band (VB), the forbidden band (FB) and the conduction band (CB). A copper wire is at room temperature. The structure of a copper crystal is to be examined using electron diffraction. Electrons, having been accelerated from rest through a potential difference V, are incident on the crystal. The de Broglie wavelength λ of the electrons is 2.6 × 10⁻¹¹ m.

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