QJEEM21Ph4c8e: JEE Main 2021 Physics - Class 12 JEEM21Ph4c8e Solution: In a photoelectric experiment ultraviolet light of wavelength…

Question

Verified Solution • 2025–26 Session moderate

In a photoelectric experiment ultraviolet light of wavelength 280 nm is used with lithium cathode having work function

ϕ

= 2.5 eV. If the wavelength of incident light is switched to 400 nm, find out the change in the stopping potential. (h = 6.63

\times

10^{$-$ 34} Js, c = 3

\times

10⁸ ms^{$-$ 1})

Accepted Answer

K E_{max} = e V_{s} = \frac{h c}{λ} - ϕ

\Rightarrow e V_{s} = \frac{1240}{280} - 2.5 =

1.93 eV

\Rightarrow V_{s_{1}} =

1.93 V .... (i)

\Rightarrow e V_{s_{2}} = \frac{1240}{400} - 2.5 =

0.6 eV

\Rightarrow V_{s_{2}} =

0.6 V .... (ii)

Δ

V =

V_{s_{1}} - V_{s_{2}}

= 1.93

-

0.6 = 1.33 V

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