Physics 9702 · AS & A Level · Energy levels in atoms and line spectra

Energy levels in atoms and line spectra — practice question

Fig. 12.1 shows some of the electron energy bands present in a solid.
(a)[3]

In isolated atoms, electron energy levels take separate, discrete values. Suggest why, in a solid, energy bands are formed instead of discrete energy levels.

(b)[5]

A light-dependent resistor (LDR) contains an intrinsic semiconductor. Use band theory to explain how the resistance of the LDR varies with light intensity when the temperature is kept constant.

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This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Electrons in adjacent atoms are close together and interact” …

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