Question

14) Photons of energy 6.0 J are incident on a metal. It is found that current flows until a stopping potential of 3.8 V is applied. A) Find the work function. (5 points) B) If the wavelength of incident photons is tripled, what is the maximum kinetic energy of ejected electrons? (5 points)

Answer 1

Energy of photons incident on the metal, E = 6.0 J

Stopping potential, V_s = 3.8 V

Maximum kinetic energy of photoelectrons, K = e V_s = 1.6 x 10^-19 x 3.8 = 6.08 x 10^-19 J

A)

Einstein’s photoelectric equation is E = W + K

Work function of the metal, W = E – K = 6.0 - 6.08 x 10^-19 = 6.0 J

Work function of the metal, W = 6.0 J

B)

The wavelength of original radiation, λ = hc/E = 6.625 x 10^-34 x 3 x 10⁸/6 = 3.31 x 10^-26 m

When the wavelength of the light is tripled, then the energy of incident photons, E1 = hc/3λ

E1 = E/3 = 6/3 = 2.0 J

Kinetic energy of emitted electrons, K = E – W = 2 – 6 = - 4 J

PLEASE NOTE:

The kinetic energy of a particle can not be negative. The energy and wavelength of the incident photon looks unrealistic and please check the data given. The energy of incident photon looks wrong.