A light beam of wavelength 400 nm is incident on a metal of work- function 2.2 eV. A particular electron absorbs a photon and makes 2 collisions before coming out of the metal
(a) Assuming that 10% of existing energy is lost to the metal in each collision find the final kinetic energy of this electron as it comes out of the metal.
(b) Under the same assumptions find the maximum number of collisions, the electron should suffer before it becomes unable to come out of the metal.

Answer

A, B, C, D

Explanation

(a) `E = (12375)/(4000) = 3.1 eV`
Energy of electron after first collision
`E_1 =90 %` of E = 2.79 eV (as 10% is lost)
Energy of electron after second collision
`E_2 = 90% of E_1 2.51 eV`
KE of this electron after emitting from the
metal surface
`=(2.51 - 2.2) eV = 0.31 eV`
(b) Energy after third collision,
`E_4 = 90% of E_3 = 2.03 eV`
So, after four collisions it becomes unable for the electrons to come out of the metal.