Question

Will photo electron be emitted by a copper surface,
whose threshold wavelength is 2800 Aº when
illuminated by visible light?​

Answer 1

The wavelength does not lie in the visible range i.e. (4000 - 7500 Aº) thus it can not emit electrons from the copper surface.

Explanation:

We know that:

The threshold wavelength λo related to work function is given by:

E = hc / λ

The wavelength = 2800 Aº

Work function "W" = h c / λo

W = 12400 / 2800

W = 4.4 e V

The value of work function is 4.4 e V

Moreover the wavelength does not lie in the visible range i.e. (4000 - 7500 Aº) thus it can not emit electrons from the copper surface.