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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Threshold frequency (ν₀)

The lowest frequency of light that can eject electrons from a given metal, ν0=Φ/h\nu_0 = \Phi/h; the matching threshold wavelength λ0=hc/Φ\lambda_0 = hc/\Phi is the longest wavelength that works. Below ν0\nu_0 nothing is ejected at any intensity.

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 line meets the frequency axis at ν0\nu_0.

Example

For Φ=4.00×10−19\Phi = 4.00\times10^{-19} J: ν0=6.04×1014\nu_0 = 6.04\times10^{14} Hz and λ0=497\lambda_0 = 497 nm. Green 550 nm light, however bright, ejects nothing from this metal.

See alsoWork function (Φ)Photoelectric effectFrequency