Question

Calculate the kinetic energy of an electron ejected by a photon with wavelength 1.57 × 102 nm from a metal with a binding energy of 3.31 ev.

Answer 1

The formula is simple.

Kinetic energy = Photon energy - Binding energy

In some places, binding energy is also called work function.

So, Photon energy =
`(hc)/(\lambda)`

=
`(6.6 * 10^(-34) * 3 * 10^8)/(1.57 * 10^2 * 10^(-9))` (Here we multiply lambda by 10^(-9) to change nm to m)

=
`1.261 * 10^(-18)` J

Change it to ev from Joule (J)
so, Photon energy =
`1.261 * 10^(-18)` J =
`\frac{1.261 * 10^(-18)} {1.6 * 10^(-19)}`
= 7.8 eV

Now, KE = 7.8 - 3.31 = 4.57 eV

Done !!!