PX262 - A1 - photoelectric effect

PX156 - A4 - the photoelectric effect

• the experimental observation that when light strikes a metal surface, electrons are emitted
• the energy of the emitted electrons depends on the frequency of the incident light, but not on its intensity
• the maximum energy:

- where,
$h=$ planck's constant
$\nu =$ frequency of incident light
$\varphi =$ work function

• the number of electron emitted is proportional to the intensity of the incident light

• in classical physics, the energy of the wave depends on its intensity

• einstein suggested that light is quantized in small portions called photons

• each photon has an energy, $E=h\nu ⟹$ higher light intensity means more photons with the same energy

• objects that in classical physics are waves can behave as particles

  • eg: visible light with a wavelength, $\lambda =550nm$, has a energy, $E=\frac{hc}{\lambda }\approx 3.6\times {10}^{-19}J$

• in QM, units of $eV$ are often used

  • $1eV=1.602\times {10}^{-19}J$
  • for a green photon, $E=2.26eV$

• also, the reduced planck's constant:

  $$\hslash =\frac{h}{2\pi }=1.055\times {10}^{-34}J{s}^{-1}$$

• units:

• $\hslash c=197eVnm$
• for a green photon: $E=2\pi \frac{\hslash c}{\lambda }=2.26eV$