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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Photoelectric effect

The ejection of electrons from a metal surface by light. Electrons appear only above a threshold frequency, however intense the light, which Einstein explained by light arriving as photons of energy hνh\nu: KEmax⁡=hν−Φ\mathrm{KE}_{\max} = h\nu - \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

No electrons below ν0\nu_0; above it, KEmax⁡\mathrm{KE}_{\max} rises with slope hh.

Example

450 nm light (4.41×10−194.41\times10^{-19} J per photon) on a metal with Φ=3.50×10−19\Phi = 3.50\times10^{-19} J ejects electrons with KEmax⁡=9.1×10−20\mathrm{KE}_{\max} = 9.1\times10^{-20} J.

See alsoWork function (Φ)Threshold frequency (ν₀)PhotonWave–particle duality