Photoelectric Effect

Theory

Light arrives in energy packets $E=hf$. An electron is ejected only if $hf>\varphi$ (the metal’s work function), leaving with $K_{max}=hf-\varphi$. Intensity changes the number of electrons, not their energy. The stopping potential is $e{V}_0=K_{max}$.

What to observe

• With λ = 400 nm on sodium, electrons come out; with red light, none — however intense.

Try this

• Increase λ until the current drops to zero: that is the threshold.
• Apply a negative voltage and find the stopping potential.

Also available in: Efeito fotoelétrico (Português) · Efecto fotoeléctrico (Español)