Question

This is a quantum physics question.

The work function for electrons ejected from a zinc surface is 4.30eV. A 15W source producing light at wavelength 253nm is illuminating that surface.

a) What is the potential needed to stop the extracted electrons?

b) What is the maximum speed of the electrons knocked out of a clean zinc surface?

c) What is the maximum number of electrons that can be extracted per second?

Answer 1

a) energy of each photon is E

E = h * c/(wavelength* e)

E = 6.626 *10^-34 * 3 *10^8/(253 * 10^-9 * 1.602 *10^-19)

E = 4.9 eV

potential needed to stop the electrons = (4.9 - 4.3)

potential needed to stop the electrons = 0.60 V

b) let the maximum speed is v

(4.9 - 4.3) * 1.602 * 10^-19 = 0.50 * 9.11 *10^-31 * v^2

solving for v

v = 4.6 *10^5 m/s

the maximum speed of the 4.6 *10⁵ m/s

c)

maximum number of electrons per sec = 15/(4.9 * 1.602 *10^-19)

maximum number of electrons per sec = 1.91 *10^19 electrons/s

the maximum number of electrons per sec is 1.91 *10¹⁹