Define Stopping Potential?

Stopping potential is the minimum negative (retarding) voltage applied to a photoelectric cell's collector plate that just stops the fastest photoelectrons from reaching it, making the photoelectric current drop to zero.

Photoelectric effect in brief

When light of enough frequency shines on a clean metal surface, it ejects electrons called photoelectrons. Each photon gives its energy to one electron. The electron uses some energy to escape the metal (work function) and keeps the rest as kinetic energy.

Role of stopping potential

Inside a photoelectric tube, photoelectrons move toward a positively charged collector plate, creating current. To measure their maximum kinetic energy (K_max), we reverse the polarity so the collector is negative. This repels electrons. The minimal voltage V₀ that reduces the current to zero is the stopping (or cut-off) potential.

Mathematical link

eV₀ = K_max = h? ? ?

Here e is the elementary charge, h is Planck's constant, ? is light frequency, and ? is the metal's work function. Measuring V₀ therefore helps find Planck's constant and verify Einstein's photoelectric equation.

Practical uses

• Determining h: Plotting stopping potential against frequency gives a straight line whose slope equals h/e.
• Material analysis: Work function values tell us about surface condition and contamination.
• Light sensors: Phototubes and photomultipliers rely on stopping potential concepts in calibration.