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Question

Silver has a work function of 4.7 eV. When ultraviolet light of wavelength 100 nm is incident upon it, a potential of 7.7 V is required to stop the photoelectrons from reaching the collector plate. How much potential will be required to stop the photoelectrons when light of wavelength 200 nm is incident upon silver?

A
1.5 V
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B
3.85 V
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C
2.35 V
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D
15.4 V
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Solution

The correct option is A 1.5 V
We know that E=hcλ E1=12.375 eV
Similarly,
E2=1237.5λ2 eV.nm=123752000=6.1875 eV


Put the values of E1 and E2 in Einstein's equation,
Now Case 1,
E1W0=eV0
12.375W0=7.7 eV
W0=4.675 eV
and
Case 2,
E2W0=eVs
Hence,
6.1875W0=eVs
Solving , we get Vs1.5 V

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