The work function for metallic caesium is 2.14 ev. calculate the
kinetic energy and the speed of the electrons ejected by light of
wavelength
(a) 750 nm,
(b) 250 nm.

Part 1) No electrons are emitted

Part 2) Energy equals 2.837eV and velocity equals

Explanation:

From the basic equation of photoelectric effect we have

where

is the energy of the incident radiation

is the work function of the metal

is the kinetic energy of the emitted electrons

Thus applying values we get

1) for wavelength of 750 nanometers we have

The energy of incident radiation equals

Since the energy of incident radiation is lesser than the work function of the metal hence no electron's will be emitted.

Part 2)

Thus kinetic energy equals

Thus speed from energy is calculated as