Photoelectric Effect Formula

Photoelectric Effect Formula

A photon is like a tiny blob of pure energy. In the photoelectric effect, an electron is hit by a wandering blob of energy and is so excited that it breaks its bond with the atom to which it is held.

We can know the energy necessary to breaks the bonds of the electrons as follows:

photon energy = work function + electron kinetic energy

The equation is:

hν = Ee + W


h: Planck's constant

ν: Frequency of the incident light

Ee: Energy of the electron

W: the work function of the material

Photoelectric Effect Formula Questions:

1) Monochromatic light of wavelength λ =400 nm strikes a plate of Cesium. Cesium has a work function of 2.14 eV. What is the energy of the electrons ejected?


From the formula of the photon's energy and using the Planck's constant h= 6.62*10(-34) J*s,

The wavelength is related to the frequency as ν =1/λ

ν = 1/400nm = 1/4*10(-7)m = 2500000 1/s = 2.5 MHz

Then the energy equation is,

Ee = h ν - W

Ee = 2.5 MHz *6.62*10(-34) J*s - 2.4 eV

Ee = 2500000 1/s *6.62*10(-34) J*s -3.4*10(-19) J

Ee = -3.4*10(-19) J = -2.12 eV

Given that the work function is greater in magnitude than the energy obtained by the electrons from the incident light, there will be no current generated.

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