Question

Photoelectrons are observed to just emit out of a material surface when the light of 620 nm falls on it with the intensity of 100 W m^-2. If the light of wavelength 400 nm is incident on the same material with an intensity of 1 W m^-2, what would be the minimum reverse potential needed to stop the outflow of the electrons?

Options

• 1 V

• 2 V

• 1.2 V

• 1.9 V

Answer 1

1.2 V

Explanation:

Work function: Φ = `1240/lambda`eV

= `1240/620`

= 2eV

Energy of the photon: U = `1240/400`

= 3.2 eV

Maximum kinetic energy of photoelectrons: 3.2 – 2 = 1.2 eV

Stopping Potential: 1.2 V