What is use of capacitors in 7805 ?

[snishanth512]

What is the purpose of capacitor in the diagram?

Are the capacitors chosen at random?

 

[Tahmid]

They are bypass/decoupling capacitors.

Check this: https://www.edaboard.com/threads/269757/
and this: https://en.wikipedia.org/wiki/Decoupling_capacitor

Are the capacitors chosen at random?

Not completely randomly, but not through exact calculations either. The values aren't too critical, so a wide range of capacitors can be used.

By the way, you should have 0.1uF capacitors, preferably ceramic, across the 2 capacitors shown in the circuit diagram.

Hope this helps.
Tahmid.