Modern Physics: The Photoelectric effect

Modern Physics: The Photoelectric effect

Click on the image for a better view.

• Sodium is the metal surface used here. When the electrons are close to the surface of the metal. The photon can impart enough energy to the electrons to escape free from the metal.
• To do that we have to overcome the work function.
• The work function is enough energy required to emit the electrons fro the surface which is in case of sodium it is 2.7 eV
• Now, will the photon have enough energy to make an electron escape sodium surface?
• for calculating the K.E. of an electron the required equation is 
  K.E. = E(ph) - W
  where K.E. is the energy of the electron after escaping the surface.
             E(ph) is the energy of the photon of a specific wavelength λ.
             W is the work function of the metal.

Let consider wavelength λ of a photon be 500nm.

Click on the image for a better view.

• As the energy comes out to be negative which is not possible. Hence, it shows that the photon does not have enough energy to escape sodium metal.
• Here we can notice that E(ph) = h*c/λ
  where E(ph) is inversely proportional to the wavelength of the photon.
• Hence we can tell that as the value of λ decreases, the energy of the photon increases.

Now what will be the minimum wavelength require to make electro escape free.

Click on the image for a better view.

• If W is known we can easily calculate. the minimum wavelength λ(min) require to make the electron escape from the surface.

For example

Click on the image for a better view.

This is a sufficient theory as per my knowledge to help you out in solving basic as well as intermediate-level problems based on the photoelectric effect.

Follow this blog page to get updates on the upcoming posts. Stay Tuned.

Thank you.

~Amol Pandit.