Question

How many of the given metals will show photoelectric effect when light of 400 nm falls on below metal? Metal Li Na K Mg Cu Ag W(eV) 2.42 2.3 2.25 3.7 4.8 4.3:

Answer 1

The correct answer is : 3

The photoelectric effect requires a photon with energy greater than the work function of the metal.
A photon's energy is provided by

\(E=\frac{hc}{\lambda}\)

Where,

h = Planck's constant, c = Velocity of light, λ = Wavelength

here given λ = 400 nm

Then E = \(\frac{6.6\times10^{-34}\times3\times10^8}{400\times 10^{-9}}\)

E in e.V = \(\frac{6.6\times10^{-34}\times3\times10^8}{400\times 10^{-9}\times1.6\times10^{-19}}\)

E = 3 eV

The metals Li, Na, K and Mg have a work function less than the Energy of a Photon. In the presence of light with a wavelength of 400nm, they exhibit a photoelectric Effect.