Question

When light of wavelength 'λ' is incident on a photosensitive surface, the stopping potential is 'V'. When light of wavelength '3λ' is incident on the same surface, the stopping potential is `"V"/6`. Threshold wavelength for the surface is _______.

Options

• 3λ

• 9λ

• 5λ

• 6λ

Answer 1

When light of wavelength 'λ' is incident on a photosensitive surface, the stopping potential is 'V'. When light of wavelength '3λ' is incident on the same surface, the stopping potential is `"V"/6`. Threshold wavelength for the surface is 5λ.

Explanation:

eV = `"hc"/lambda - "hc"/lambda_0`

e`"V"/6 = "hc"/(3lambda) - "hc"/lambda_0`

`therefore 5 "eV"/6 = "hc"/lambda - "hc"/(3lambda)`

eV = `4/5 "hc"/lambda`

Hence, `4/5 "hc"/lambda = "hc"/lambda - "hc"/lambda_0`    or  `1/lamda_0 = 1/lambda - 4/5 lambda`

λ₀ = 5λ