Dual Nature — Photoelectric Effect (Medium)

Quick Recap — Photoelectric Effect

• Einstein's equation: $KE_{max}=hf-\phi=hf-hf_0$, where $\phi=hf_0=\dfrac{hc}{\lambda_0}$ is the work function.
• Stopping potential: $eV_0=KE_{max}=hf-\phi$; a graph of $V_0$ versus $f$ is a straight line of slope $\dfrac{h}{e}$.
• Key facts: emission is instantaneous and needs $f>f_0$; the photocurrent $\propto$ intensity, but $KE_{max}$ depends only on frequency (not intensity).
• Photon: energy $E=hf=\dfrac{hc}{\lambda}$ (use $E\text{(eV)}=\dfrac{1240}{\lambda\text{(nm)}}$); momentum $p=\dfrac{h}{\lambda}=\dfrac{E}{c}$.

Worked mini-example. 400 nm light ($E=\dfrac{1240}{400}=3.1$ eV) on a metal of work function 2 eV gives $KE_{max}=3.1-2=1.1$ eV, so the stopping potential is 1.1 V.