"The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0.710 V. When the incident wavelength is changed to a new value, the stopping potential is 1.43 V. The new wavelength is :"

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"From the photoelectric effect equation

${{hc} \over \lambda } = \phi + e{v_s}$

so, $e{v_{{s_1}}} = {{hc} \over {{\lambda _1}}} - \phi$ .....(i)

$e{v_{{s_2}}} = {{hc} \over {{\lambda _2}}} - \phi$ ......(ii)

Subtract equation (i) from equation (ii)

$$e{v_{{s_1}}} - e{v_{{s_2}}} = {{hc} \over {{\lambda _1}}} - {{hc} \over {{\lambda _2}}}$$

$${v_{{s_1}}} - {v_{{s_2}}} = {{hc} \over e}\left( {{1 \over {{\lambda _1}}} - {1 \over {{\lambda _2}}}} \right)$$

$(0.710 - 1.43) = 1240\left( {{1 \over {491}} - {1 \over {{\lambda _2}}}} \right)$

${{ - 0.72} \over {1240}} = {1 \over {491}} - {1 \over {{\lambda _2}}}$

${1 \over {{\lambda _2}}} = {1 \over {491}} + {{0.72} \over {1240}}$

${1 \over {{\lambda _2}}} = 0.00203 + 0.00058$

${1 \over {{\lambda _2}}} = 0.00261$

${\lambda _2} = 383.14$

${\lambda _2} \simeq 382$ nm"

The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0.710 V. When the incident wavelength is changed to a new value, the stopping potential is 1.43 V. The new wavelength is :

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The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0.710 V. When the incident wavelength is changed to a new value, the stopping potential is 1.43 V. The new wavelength is :

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