3.2.2.1
Stopping potential measures maximum kinetic energy
The Photoelectric Effect — AQA A-Level Physics
Key Definition
Stopping potential — The potential difference required to stop the emission of photoelectrons, i.e. to reduce the photoelectric current to zero.
$$\begin{aligned}
eV_s &= E_{k(max)} \\
&= hf - \phi
\end{aligned}$$
$$E_{k(\max)} = eV_s$$
- $E_k(max)$: maximum kinetic energyThe capacity to do work. Measured in joules (J).The energyThe capacity to do work. Measured in joules (J). an object possesses due to its motion. of photoelectrons (J)
- $e$: chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). on an electron (1.60 × 10⁻¹⁹ C)
- $V_s$: stopping potentialThe minimum potential difference required to stop the most energetic photoelectrons emitted in the photoelectric effect. (V)
- A p.d. is applied to oppose the motion of photoelectrons between emitter and collector plates.
- When the p.d. equals $V_s$, even the fastest electrons cannot reach the collector and the currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). drops to zero.
- The stopping potentialThe minimum potential difference required to stop the most energetic photoelectrons emitted in the photoelectric effect. is independent of intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. — it depends only on photonA quantum (discrete packet) of electromagnetic radiation. Its energy is proportional to its frequency. frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). and work functionThe minimum energyThe capacity to do work. Measured in joules (J). required to liberate an electron from the surface of a metal..
Examiner Tips and Tricks
Stopping potentialThe minimum potential difference required to stop the most energetic photoelectrons emitted in the photoelectric effect. is technically negative (it opposes electron motion), but in calculations you use its magnitude to find $E_{k(\max)}$.