11Class 12 Physics

Dual Nature of Radiation and Matter formulas

Photoelectric effect and de Broglie formulas for Dual Nature of Radiation and Matter. It's short and scoring, with mostly direct numericals.

Photoelectric effect

Photon energy
E=hν=hcλ\displaystyle E = h\nu = \frac{hc}{\lambda}

hc ≈ 1240 eV nm.

Photon momentum
p=hνc=hλ\displaystyle p = \frac{h\nu}{c} = \frac{h}{\lambda}
Einstein's equation
Kmax⁡=hν−ϕ0\displaystyle K_{\max} = h\nu - \phi_0
Stopping potential
eV0=Kmax⁡\displaystyle eV_0 = K_{\max}
Work function
ϕ0=hν0\displaystyle \phi_0 = h\nu_0

ν₀ is the threshold frequency.

Matter waves

de Broglie wavelength
λ=hp=hmv\displaystyle \lambda = \frac{h}{p} = \frac{h}{mv}
From kinetic energy
λ=h2mK\displaystyle \lambda = \frac{h}{\sqrt{2mK}}
Electron through potential V
λ=1.227V nm\displaystyle \lambda = \frac{1.227}{\sqrt V}\ \text{nm}

Where students slip up

  • Thinking brighter light gives faster electrons. Intensity changes the number of electrons, and frequency changes their energy.
  • Expecting emission below the threshold frequency, however bright the light. It doesn't happen.
  • Mixing units. Convert between eV and joules before using E = hν in SI.

Try it on your weakest chapter.

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