Question

1. The work-function of rubidium metal is 208 kJ/mol, which means that it takes 208 kJ to remove 1 mol of electrons from the surface of solid rubidium metal.

a) What is the maximum wavelength of light needed to cause photoeffect with Rb(s)? (575 nm)

b) What color is the light in part a?

c) In a different photoeffect experiment with Rb(s), electrons with the de Broglie wavelength of 0.744 nm are generated. What is the wavelength of radiation used in this experiment?

d) What kind of radiation is used in part c?

(I got 575 nm for part a. I'm having trouble with part c and d)

Answer 1

part c

from einsteins equation,

(hc/l) = hv0 + K.E --- 1

from debroglies equation

   l = h/mv = h/(sqrt(m*2K.E))

K.E = kinetic energy = ?

   l = wavelength = 0.744 nm = 7.44*10^-10 m

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

   h = 6.625*10^-34 j.s

(7.44*10^-10) = (6.625*10^-34)/(sqrt(9.11*10^-31*(2*x)))

x = kinetic eenrgy of electron = 4.352*10^-19 joule

from equation 1

hv0 = 208*10^3/(6.023*10^23) = 3.453*10^-19 joule

so that,

(6.625*10^-34*3*10^8/x) = (3.453*10^-19)+(4.352*10^-19)

x = wave length of incident light = 2.55*10^-7 m

     = 255 nm

part D

radiation used in part c = UV