Educator

Dual Nature of Light

• Photoelectric effect: when light falls on a metal surface, electrons are emitted with kinetic energy K.
• Some experimental facts:
• The maximum value of K is independent of the light intensity.
• No electrons are emitted if the incident photon frequency is below a threshold value.
• K increases with increasing photon frequency.
• Einstein’s explanation:
• Light is a stream of quanta (photons). Each photon has energy E = hf, where h is Planck’s constant and f is the frequency.
• A photon gives all its energy to a single electron.
• K_max = hf – W, where W is the work function.
• Compton scattering: when a photon is scattered from an electron, a change in wavelength of the photon takes place.