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Solution


Q.

A light source of wavelength λ illuminates a metal surface and electrons are ejected with maximum kinetic energy of 2 eV. If the same surface is illuminated by a light source of wavelength λ2, then the maximum kinetic energy of ejected electrons will be (The work function of metal is 1 eV)          [2025]
1 2 eV  
2 6 eV  
3 5 eV  
4 3 eV  

Ans.

(3)

Einstein's photoelectric equation

KE=hcλ–ϕ0

2 eV=hcλ–1 eV

hcλ=3 eV

KE=hc(λ/2)–ϕ0=6 eV–1 eV=5 eV