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Stopping potential
Intermediate
Voltage that stops the fastest photoelectrons.
eV₀ = hf − φThe reverse voltage needed to stop the fastest photoelectrons: eV₀ = K_max = hf − φ. A graph of V₀ vs f has slope h/e, letting you measure h.
f = 8×10¹⁴ Hz, φ = 2.3 eV: V₀ = 1.0 V.
Independent of intensity.
In more detail
The stopping potential is the voltage needed to stop the fastest photoelectrons, giving eV0 = KEmax. Measuring it for different frequencies gives Planck's constant.
Real-world uses
- Experiments measure stopping potentials to determine h and the work function.
- Photoelectric detectors use stopping potential to analyse electron energies.
- Physicists measure the stopping potential to find Planck's constant from the photoelectric effect.
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Frequently asked questions
How is it measured?
By applying a reverse voltage until the photocurrent drops to zero.
What is the slope of the graph?
Planck's constant divided by the electron charge.
Why does the stopping potential depend on frequency?
The maximum kinetic energy of the electrons rises with photon frequency, so a larger voltage is needed to stop them.
Related topics in Quantum Mechanics
Photoelectric effect · Einstein's photoelectric equation · Threshold frequency · Photon momentum · Compton effect · Pair production