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The photoelectric work function of a metal is 1 eV. Light of wavelength λ=3000 ångström falls on it. The photoelectrons come out with a maximum velocity of:

Asked in AIPMT 1991 · Speed and kinetic energy of the photoelectrons

Answer: (4) 10⁶ m s⁻¹

Step-by-step solution

Photon energy: E=(hc)/λ=(12400 eV ångström)/(3000 ångström)=4.13 eV.

Maximum kinetic energy: Kₘₐₓ=4.13-1=3.13 eV=5.0×10⁻¹⁹ J.

v=√(2Kₘₐₓ)/m=√(2×5.0×10⁻¹⁹)/(9.1×10⁻³¹).

v=√1.10×10¹²=1.05×10⁶ m s⁻¹.

To the nearest option, 10⁶ m s⁻¹.

Why the other options are wrong

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