When a metal plate is exposed to a monochromatic beam of light of wavelength 400 nm, a negative potential of 1.1 V is needed to stop the photocurrent. Find the threshold wavelength for the metal.

Given, wavelength

Potential (i.e.; stopping potential) =1.1V

From Einstein’s photoelectric equation,

⇒

Where is the threshold wavelength,

is the wavelength of light,

h is Planck’s constant,

c is the speed of light,

e is the charge on electron,

is the stopping potential

⇒

⇒

⇒

⇒

∴ (threshold frequency) = m.