The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV, and the stopping potential for a radiation incident on this surface 5 V , the incident radiation lies in :
A
X ray region
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B
ultra violet region
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C
infra red region
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D
visible region
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Solution
The correct option is B ultra violet region
Given,
V0=5V
hcλ=6.2eV
From Einstein formula,
W=hcλ−eV0=6.2eV−5eV
W=1.2eV
hcλi=1.2eV
λi=12400eV1.2eV=10333×10−10m
λi=1033.3nm
The wavelength of incident wave comes in the region of ultra violet.