Light of energy 2.0 eV falls on a metal of work function 1.4 eV. The stopping potential is

The energy of the incident light is given as 2.0 eV and the work function (the minimum energy needed to remove an electron) of the metal is given as 1.4 eV.

The maximum kinetic energy of the ejected electrons is given by the difference between the energy of the incident light and the work function of the metal. This is based on the photoelectric effect equation:

K.E_max = E - φ

where: K.E_max is the maximum kinetic energy of the ejected electrons, E is the energy of the incident light, and φ is the work function of the metal.

Substituting the given values:

K.E_max = 2.0 eV - 1.4 eV = 0.6 eV

The stopping potential (V) is the potential needed to stop the fastest moving photoelectrons and can be calculated from the maximum kinetic energy using the equation:

K.E_max = eV

where: e is the charge of an electron (approximately 1.6 x 10^-19 C).

Rearranging for V gives:

V = K.E_max / e

Substituting the value for K.E_max gives:

V = 0.6 eV / 1.6 x 10^-19 C = 3.75 x 10^-19 J / 1.6 x 10^-19 C = 2.34 V

So, the stopping potential is approximately 2.34 V.