• Tags: work-function, threshold, metals
• Difficulty: Moderate

The work function φ is the minimum energy needed to eject an electron from the metal surface. It is a property of the metal. Threshold frequency: $f_{0}$ = φ/h. Threshold wavelength: λ_{0} = hc/φ = 1240/φ(eV) nm. Metals with low work functions (Cs, K, Na) emit photoelectrons with visible light. Metals with high work functions (Pt, W) require UV light.

JEE commonly asks: given two metals and one light source, determine which shows photoelectric effect. Compare λ_light with λ_{0} of each metal: emission occurs only if λ_light < λ_{0} (equivalently $f_{light}$ > $f_{0}$). The photoelectric effect is a surface phenomenon — electrons near the surface escape most easily.