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Chemistry Question on Electrochemistry

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

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=hcλE=\frac{hc}{\lambda}

Where,

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

here given λ = 400 nm

Then E = 6.6×10−34×3×108400×10−9\frac{6.6\times10^{-34}\times3\times10^8}{400\times 10^{-9}}

E in e.V = 6.6×10−34×3×108400×10−9×1.6×10−19\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.