Practice portal › Dual Nature of Matter and Radiation › Einstein's Photoelectric Equation and Work Function
Asked in GUJCET 2026 · Speed and kinetic energy of the photoelectrons
Given: cut-off (stopping) voltage V₀ = 1.5 V.
Idea: the stopping potential is the retarding voltage that just turns back the fastest photoelectron, so Kₘₐₓ = eV₀.
An electron pushed through 1 V gains exactly 1 eV -- that is what the electron-volt means.
So Kₘₐₓ = e×1.5 V = 1.5 eV, which in joule is 1.5×1.6×10⁻¹⁹ = 2.4×10⁻¹⁹ J.
The energy is therefore 1.5 eV, and the two joule options are the same number with the wrong unit.
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