In a Frank-Hertz experiment, an electron of energy 5.6 eV passes through mercury vapour and emerges with an energy 0.7 eV. The minimum wavelength of photons emitted by mercury atoms is close to
A
220 nm
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B
253 nm
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C
550 nm
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D
750 nm
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Solution
The correct option is B 253 nm E1 = 5.6 eV E2 = 0.7 eV ΔE = 5.6- 0.7 = 4.9 eV λ = hcΔE= 12424.9≃253 nm