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Question

Light of wavelength 2000 ˙A falls on a metallic surface, for which a stopping potential of 2 V is required. Find the wavelength of the incident radiation for which the stopping potential required is 5 V.

A
1348 ˙A
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B
1200 ˙A
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C
1648 ˙A
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D
2300 ˙A
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Solution

The correct option is A 1348 ˙A
According to Einstein's photoelectric equation,

eV0=hcλϕ

As the metal surface is the same in both cases, work function remains the same.

eV1+hcλ1=eV2+hcλ2

hcλ2hcλ1=e(V2V1)

12400 eV˙A(1λ212000 ˙A)=3 eV

12400 ˙A(2000 ˙Aλ2)=3×2000 ˙A λ2

2000 ˙Aλ2=3×20124λ2

2000 ˙A=4631λ2

λ2=1347.82 ˙A

Hence, option (A) is correct.

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