Question

# A stopping potential of 0.82 volt is required to stop the photo electrons emitted from a metallic surface by light of wavelength 4000ËšA. The stopping potential for wavelength 3000ËšA will be

A
1.1 volt
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B
1.85 volt
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C
2.03 volt
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D
2.5 volt
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Solution

## The correct option is B 1.85 voltHere, a stopping potential of 0.82 volt is required to stop the photo electrons emitted from a metallic surface by light of wavelength 4000A∘, henceeV=hν−ϕwhere, V is the stopping potential, e is the electronic charge, ν is the frequency of incident light and ϕ is photoelectric work function of metal, h is Plank's constant.eV=hcλ−ϕ1.6×0.82×10−19=6.6×10−34×3×1084000×10−10−ϕ1.312×10−19=4.95×10−19−ϕϕ=(4.95−1.312)×10−19ϕ=3.638eVThe stopping potential for wavelength 3000A∘V=hcλ−ϕeV=6.6×10−34×3×1083000×10−10−3.638×10−191.6×10−19 V=2.9621.6V=1.85VSo, the answer is option (B).

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