Question

What is the maximum kinetic energy of an ejected electron if magnesium metal is irradiated with 294 nm light? The threshold wave length for a magnesium metal surface is 339nm.

Answer 1

The energy is given by the formula

E = hc/ L

h is the planck's constant = 6.63 x 10^-34 J/s

c is the speed of light = 3 x 10⁸ m / s

L is the wavelength = 294 nm or 2.94 x 10^-7 m

putting all the values,

E = (6.63 x 10^-34 x 3 x 10⁸) / 2.94 x 10^-7

E = 6.76 x 10^-19 J

The threshold energy will be given as

E = (6.63 x 10^-34 x 3 x 10⁸) / 3.39 x 10^-7

E = 5.87 x 10^-19 J

The difference of these energies goes in the Kinetic energu of electron

So KE of electron = (6.76 x 10^-19) - (5.87x 10^-19)

= 8.9 x 10^-20 J

answered by: anonymous