Question

In a photoelectric experiment, ultraviolet light of wavelength 280 nm is used with a 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 × 10^-34 Js, c = 3 × 10⁸ ms^-1)

Options

• 1.9 V

• 1.1 V

• 1.3 V

• 0.6 V

Answer 1

1.3 V

Explanation:

According to Einstein's equation,

`(eV_0)_1 = (hc)/(lambda_1) - W` .........(i)

and `(eV_0)_2 = (hc)/(lambda_2) - W` ........(ii)

Taking eqn (ii) and subtracting it from eqn (i),

`e(V_{01} - V_{02}) = hc{1/lambda_1 - 1/lambda_2}`

`(V_{01} - V_{02}) = (hc)/e{1/lambda_1 - 1/lambda_2}`

We are given λ₁ = 280 nm, λ₂ = 400 nm

Change in V's stopping potential,

`((6.63 xx 10^-34 xx 3 xx 10^8)/(1.6 xx 10^-19))[1/280 - 1/400] xx 10^9`

⇒ `(12.43 xx 10^2 xx 120)/(280 xx 400)`

⇒ (V₀₁ - V₀₂) = 1.33 V