Question

# A certain metallic surface is illuminated with monochromatic light of wavelength, λ. The stopping potential for photo-electric current for this light is 3V0. If the same surface is illuminated with light of wavelength 2λ, the stopping potential is V0. The threshold wavelength for this surface for photo-electric effect is:

A
λ4
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B
λ6
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C
6λ
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D
4λ
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Solution

## The correct option is D 4λFrom photoelectric equation,K.E.max=hν−hνthreshold...(i)where ν is frequency of light ν=cλfrom equation (i)3eV∘=hcλ−hcλthreshold...(ii)eV∘=hc2λ−hcλthreshold...(iii)multiplying (iii) by 3 and subtracting (ii)0=hc2λ−2hcλthresholdλthreshold=4λ

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