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Why are potassium and caesium rather tha...

Why are potassium and caesium rather than lithium used in photoelectric cells ?

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Potassium and caesium have much lower ionisation enthalpy than that of lithium. As a result, these metals on exposure to light, easily emit electrons but lithium does not. Therefore, `K` and `Cs` rather than `Li` are used in photoelectric cells.
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