Question

Answer the following giving reason:

If one goes on increasing the wavelength of light incident on a metal surface, keeping its intensity constant, emission of photo electrons stop at a certain wavelength for this metal.

Answer 1

The photoelectric effect transpires solely when the energy of the incident photons meets or exceeds the metal’s work function (Φ). The energy of a photon is expressed as:

E = `(hc)/lambda`

As the wavelength (λ) increases, the energy of the photon decreases. When the wavelength attains a threshold value (λ_th), associated with the work function:

λ_th = `(hc)/phi`

The photon energy becomes insufficient to dislodge electrons, leading to the cessation of photoemission. Beyond this threshold wavelength, no electrons are emitted, irrespective of light intensity.