Question

6a) The work function of a clean tungsten surface is 4.50 eV. Find the speed of the fastest electrons emitted from a tungsten surface when light of 5-eV photon energy shines on the surface.

Answer 1

Here is what I solved before, please modify the figures as per your question. Please let me know if you have further questions. If this helps then kindly rate 5-stars

The work function of tungsten is 4.50 eV. Calculate the speed of the fastest electrons ejected from a tungsten surface when light whose photon energy is 5.64 eV shines on the surface (answer in km/s).

solution:

Data:

Work function, ? = 4.5 eV

Energy of photon, E = 5.64 eV

Mass of electron, m = 9.11 x 10^-31 kg

Solution:

Maximum kinetic energy, K = (1/2) m v^2

            (1/2) m c^2 ( v/c)^2 = E - ?

                      m c^2 ( v/c)^2 = 2 ( E - ? )

                                  ( v/c)^2 = 2 ( E - ? ) / m c^2

                                           v = c ? [ 2 ( E - ? ) / m c^2]

                                          

By substituting the values,

v = ( 2.998 x 10^8 m/s) ? [ 2 (5.64 eV - 4.5 eV ) / 511 x 10^3 eV ]

   = 6.3327 x 10^5 m/s

   = 633.3 km/s

Ans:

v = 633.27 km/s