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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Planck's constant

The constant h=6.626×10−34h = 6.626\times10^{-34} J s that links the energy of a photon to its frequency, E=hνE = h\nu. It also appears in the de Broglie wavelength λ=h/mv\lambda = h/mv and in the uncertainty principle Δx Δp≥h/4π\Delta x\,\Delta p \ge h/4\pi.

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

In the photoelectric effect the slope of the line is hh.

Example

A photon of frequency 5.00×10145.00\times10^{14} Hz has E=(6.626×10−34)(5.00×1014)=3.31×10−19E = (6.626\times10^{-34})(5.00\times10^{14}) = 3.31\times10^{-19} J.

See alsoPhotonde Broglie wavelengthHeisenberg uncertainty principle