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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Work function (Φ)

The minimum energy needed to remove an electron from the surface of a metal, written Φ\Phi. It is a property of the metal, and it sets the threshold: ν0=Φ/h\nu_0 = \Phi/h and λ0=hc/Φ\lambda_0 = hc/\Phi.

Photoelectric effect for sodiumKinetic energy of ejected electrons against light frequency. Below the threshold frequency ν₀ ≈ 5.5 × 10¹⁴ Hz no electrons are ejected, however bright the light. Above it the kinetic energy rises in a straight line of slope h; extended back, the line meets the energy axis at minus the work function.ν₀1015−Φ05frequency (10¹⁴ Hz)KE of electron (10⁻¹⁹ J)no electronsslope = h

The yy-intercept of the KEmax⁡\mathrm{KE}_{\max} line is −Φ-\Phi.

Example

A metal whose threshold wavelength is 600 nm has Φ=hc/λ0=(1.986×10−25)/(6.00×10−7)=3.31×10−19\Phi = hc/\lambda_0 = (1.986\times10^{-25})/(6.00\times10^{-7}) = 3.31\times10^{-19} J, or 2.07 eV.

See alsoPhotoelectric effectThreshold frequency (ν₀)Electron volt (eV)