Question

Calculate the energy of photon in electron volt for radiation of wavelength 1m

Answer 1

To find the energy of a photon you use the Planck Expression:

E=hf

h is the Planck Constant which = 6.63×10−34xJ.s

f is the frequency

This becomes:

E=hcλ

c is the speed of light = 3.00×108xm/s

λ is the wavelength

∴E=6.63×10−34×3.00×108/490×10−9xJ

E=4.00×10−19xJ

If 1 Coulomb of charge is moved through a potential difference of 1 Volt then 1 Joule of work is done.

The electron volt is the work done in moving 1 electron through a potential difference of 1 Volt.

The charge on the electron is taken here to be 1.60×10−19xC

∴1eV=1.60×10−9xJ

∴ The energy of the electron in electron volts

=4.00×10−191.60×10−19=2.5xeV