Modern Physics 2 Question 13

13. 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 and the corresponding stopping potential (V0) are given below:

(2016 Adv.)

λ(μm) V0 (Volt)
0.3 2.0
0.4 1.0
0.5 0.4

Given that c=3×108ms1 and e=1.6×1019C, Planck’s constant (in units of J-s) found from such an experiment is)

(a) 6.0×1034

(c) 6.6×1034

(b) 6.4×1034

(d) 6.8×1034

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Solution:

hcλφ=eV0hc0.3×106φ=2ehc0.4×106φ=1e

Subtracting Eq. (ii) from Eq. (i)

hc10.310.4106=ehc0.10.12×106=eh=0.64×1033=6.4×1034Js



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