Photoelectric Effect - I

We all might have seen solar panels.

We can see then on the rooftops of the buildings, street lights and even in the calculators.

Solar panels are used to convert solar energy into electricity.

And this electricity can be used to charge batteries or lighting bulbs and other appliances.

The solar panels have a device called photoelectric cell which converts the solar energy into the electricity.

The photoelectric cells work on the principle of photoelectric effect.

Let’s discuss the photoelectric effect.

Let’s first understand the electronic emissions.

Suppose we have a metal surface having many free electrons and we are giving energy in any form to the metal surface.

Then the some of the free electrons will come out from the metal surface and this phenomenon is called elctronic emission.

And Sir J. J. Thomson was used this effect to discover the electrons.

The velocity of leaving electrons may be high or may be low depending upon the energy which has been provided.

Now, the every metal has a unique property named as work function. It is the minimum energy required for electrons to leave the metal surface.

The provided energy can be of various form like heat energy, electrical energy, etc.

When the provided energy is in the form of heat, then the electronic emission is called thermionic emission.

Now, when a metal surface is placed in an electric field, the electrons rotating in their orbits experience a force.

Due to this force, the electrons will leave the metal surface and this type of emission is called field emission.

Now, after the J. J, Thomson experiment for the discovery of the electron, Hertz thought about to discover something new in 1887.

He thought that the light is also a form of energy. So, when we apply a light on the metal surface for long time then the electrons will leave the metal surface.

And he did the similar experiment successfully on the same plate as in the J. J. Thomson experiment.

So, this emission was named as photoelectric emission.

After that he did also a similar experiment and this time there is no battery. Only a plate of positive and negative charge connected through ammeter.

And in this experiment, after striking the light, some deflection was saw by the Hertz in the ammeter. That means current is flowing through this circuit.

Hence, simply with the help of light, he could produce a current.

And this principle is used in the solar panels to produce electricity.

And provides us the cost efficient and environment friendly electricity.

Revision

When the heat energy is provided for the electronic emission, then this is called thermionic emission.

When the metal surface is placed in the electric field then emission is called field emission.

And when the light energy is used for emission then this type of emission is called photoelectric emission.

Another experiment was also done by Hertz on behalf of which solar panels work.

The End