Photoelectric Effect Reference Cheat Sheet

Key Facts

• Photon energy is given by $E = hf$, where $h$ is Planck’s constant and $f$ is the light frequency.
• Using wavelength, photon energy can be written as $E = \frac{hc}{\lambda}$, where $c$ is the speed of light and $\lambda$ is wavelength.
• The work function $\phi$ is the minimum energy needed to remove one electron from a metal surface.
• Einstein’s photoelectric equation is $K_{\max} = hf - \phi$, where $K_{\max}$ is the maximum kinetic energy of emitted electrons.
• The threshold frequency is $f_0 = \frac{\phi}{h}$, and no electrons are emitted when $f < f_0$.
• The stopping potential satisfies $eV_s = K_{\max}$, so $V_s = \frac{K_{\max}}{e}$.
• Increasing light intensity increases the number of emitted electrons if $f > f_0$, but it does not increase $K_{\max}$.
• A graph of $K_{\max}$ versus $f$ has slope $h$ and vertical intercept $-\phi$.

Vocabulary

Photon

A photon is a discrete packet of electromagnetic energy with energy $E = hf$.

Work function

The work function $\phi$ is the minimum energy required to remove an electron from a metal surface.

Threshold frequency

The threshold frequency $f_0$ is the minimum light frequency needed to eject electrons, given by $f_0 = \frac{\phi}{h}$.

Photoelectron

A photoelectron is an electron emitted from a material after absorbing energy from a photon.

Stopping potential

The stopping potential $V_s$ is the voltage needed to reduce the maximum photoelectron kinetic energy to $0$.

Maximum kinetic energy

The maximum kinetic energy $K_{\max}$ is the greatest kinetic energy of emitted electrons, equal to $hf - \phi$.