Previous Year Question

Albert Einstein was awarded the 1921 Nobel Prize in Physics. The Nobel citation honoured him for his contributions to Theoretical Physics and especially for the discovery of the law of the photoelectric effect.

The Photoelectric Effect is the phenomenon in which electrons are emitted from a metal surface when electromagnetic radiation of sufficient frequency falls on it. These emitted electrons are called photoelectrons.

In 1905, Einstein explained this phenomenon by proposing that light energy is not transferred continuously but in discrete packets called quanta, later known as photons.

The energy of a photon is—

E = hν

where h = Planck constant and ν = frequency of the radiation.

If the energy of a photon is below the work function of the metal, merely increasing the intensity of light cannot initiate photoelectron emission. Thus, the photoelectric effect provided important evidence for the particle/quantum nature of light.

Although Einstein is famously associated with the Theory of Relativity, he was not awarded the Nobel Prize for Relativity; the award particularly recognized the law of the photoelectric effect.

The 1921 Nobel Prize was actually presented to him in 1922, as the 1921 Physics Prize had been reserved until the following year.