Eduprobe
Question:
In a historical experiment to determine Planck's constant, a metal surface was irradiated with light of different wavelengths. The emitted photoelectron energies were measured by applying a stopping potential. The relevant data for the wavelength (λ) of incident light at the corresponding stopping potential (V0) are given below:
λ(µm) V0(Volt)
0.3 2.0
0.4 1.0
0.5 0.4
Given that c=3×10⁸ms⁻¹ and e=1.6×10⁻¹⁹C, Planck's constant (in units of J s) from such an experiment is :
6.0×10⁻³⁴
6.4×10⁻³⁴
6.6×10⁻³⁴
6.8×10⁻³⁴
Solution:
hc/λ - φ = eV0
From given data,
hc/(0.3×10⁻⁶) - φ = 2e
hc/(0.4×10⁻⁶) - φ = e
Subtracting, we get,
hc(1/(0.3×10⁻⁶) - 1/(0.4×10⁻⁶)) = e
h = e/(c(1/(0.3×10⁻⁶) - 1/(0.4×10⁻⁶)))
= 6.4 × 10⁻³⁴ Js
Answer is option B.