Question

It requires a photon with a minimum energy of 4.41 ✕ 10-19 J to emit electrons from sodium metal. c) If sodium is irradiated with light of 389 nm, what is the maximum possible kinetic energy of the emitted electrons?(answer in J) (d) What is the maximum number of electrons that can be freed by a burst of light (λ = 389 nm) whose total energy is 1.20 µJ? (answer in electrons)

Answer 1

c) Energy(E) = hc/l

E = ? joule

   h = planks constant = 6.625*10^-34 j.s

   c = light velocity = 3*10^8 m/s

   l = wavelength = 389 nm = 389*10^-9 m

E = (6.625*10^-34)*(3*10^8)/(389*10^-9)

E = 5.11*10^-19 joule

Kinetic eenrgy of electrons (K.E) = E-E0

           = (5.11*10^-19)-(4.41*10^-19)

           = = 7*10^-20 j
d)

minimum energy required = 4.41*10^-19 joule

total energy available = 1.20 µJ

No of elctrons can be removed = (1.2*10^-6)/(4.41*10^-19)

                  = 2.72*10^12