Question

The work function of silicon is 7.24 × 10–19 J. Calculate the velocity of the emitted electron if the surface is irradiated with UV radiation of wavelength 240 nm. If lower velocity electrons were required, should a material with higher or lower work function be used? Explain.

Answer 1

Eo = 7.24*10^-19 J

lets calculate the energy of wavelength

use:

E = h*c/lambda

=(6.626*10^-34 J.s)*(3.0*10^8 m/s)/(2.4*10^-7 m)

= 8.28*10^-19 J

KE of electron = E - Eo

= 8.28*10^-19 J - 7.24*10^-19 J

= 1.04*10^-19 J

mass of electron, m = 9.11*10^-31 kg

Use:

KE = 0.5*m*v^2

1.04*10^-19 = 0.5*9.11*10^-31*v^2

v = 4.78*10^5 m/s

Answer: 4.78*10^5 m/s

for electron to have lower velocity (means kinetic energy of electrons should be less), Eo should be more

So, material with higher work function be used