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Question:

In a photoelectric experiment, the wavelength of the light incident on a metal is changed from 300nm to 400nm. The decrease in the stopping potential is close to: (hc = 1240nm-V) 1.0V 1.5V 2.0V 0.5V

2.0V

0.5V

1.0V

1.5V

Solution:

The correct option is B
1.0V
hc/λ₁ = Φ + eV₁ (i)
hc/λ₂ = Φ + eV₂ (ii)
(i) - (ii) hc(1/λ₁ - 1/λ₂) = e(V₁ - V₂) ⇒ V₁ - V₂ = hc/e(λ₂ - λ₁)/λ₁λ₂ = (1240nm⁻¹V)100nm/(300nm × 400nm) = 1V.