Stopping potential
The retarding potential difference required to reduce the kinetic energy of the most energetic photoelectrons to zero, preventing them from reaching the collector. Stopping potential V_s satisfies eV_s = KE_max = hf - Φ, where KE_max is the maximum kinetic energy of ejected electrons.
Formula
eV_s = hf − Φ
Real World
Robert Millikan's 1916 experiments at the University of Chicago measured stopping potentials for different light frequencies and produced the first accurate value of Planck's constant.
Exam Focus
When plotting V_s against f, the gradient equals h/e and the x-intercept gives threshold frequency — state both explicitly.
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