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.
$(h = 6.63 \times 10^{- 34} J s, c = 3 \times 10^{8} {m s}^{- 1})$

Question

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.

$(h = 6.63 \times 10^{- 34} J s, c = 3 \times 10^{8} {m s}^{- 1})$

TestHub · Accepted Answer

From the photoelectric equation, e V 0 = h c λ − ϕ Using this equation for the given two cases, e V 1 = h c 280 nm − ϕ e V 2 = h c 400 nm − ϕ On subtracting, e V 1 − V 2 = 1240 120 280 × 400 = 1.3 eV ⇒ V 1 − V 2 = 1 . 3 V

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