Practice portal › Dual Nature of Matter and Radiation › Einstein's Photoelectric Equation and Work Function

A photon of energy 8 eV is incident on a metal surface of threshold frequency 1.6×10¹⁵ Hz. The maximum kinetic energy of the photoelectrons emitted is ______. (Take h = 6.6×10⁻³⁴ J s; 1 eV = 1.6×10⁻¹⁹ J)

Asked in GUJCET 2008 · Speed and kinetic energy of the photoelectrons

• (1) 4.2 eV
• (2) 2.8 eV
• (3) 1.4 eV
• (4) 0.8 eV

Step-by-step solution

Why the other options are wrong

• (1) No single slip gives 4.2 eV. It would need a work function of 3.8 eV, that is, a threshold frequency near 9.2×10¹⁴ Hz, not 1.6×10¹⁵ Hz.
• (2) No single slip gives 2.8 eV; it is exactly twice the right value. The work function hf₀ = 6.6 eV leaves 8 - 6.6 = 1.4 eV.
• (4) No single slip gives 0.8 eV. It would need a work function of 7.2 eV, that is, f₀ ≈ 1.75×10¹⁵ Hz.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.