Topic under the Chapter: Electrostatics
1. Short Introduction
To understand Charge Induction, we need to first know about ‘free electrons’. These free electrons behave very similarly to the gas atoms in a container. Both of them are under continuous random motion throughout the space given to them.
Charge induction forms the working principle behind devices such as capacitors. The understanding that you would obtain by reading this concept would help you see how metals and non-metals behave in practical circuits.
Free electrons are nothing but some loosely bonded valence electrons that come out of the atom very easily, just as the loosely stitched button comes out of the shirt very easily!
Note that:
- A neutral body has an equal number of positive charges and negative charges. The presence of free electrons doesn’t disturb the neutrality of the body, as free electrons are also negative charges, but the only difference is that they are free to move inside the body
2. Induction in Metal and Non-metals
When we talk of bodies, we classify them as –
- Metals – The ones in which there are a lot of free electrons
- Non-metals – electrons are bound to the Atom tightly (the atom loves them!)
2.1 Charge Induction in Metals
Now suppose you have a metal conductor placed in a region. And you bring a positive charge ‘+q’ in that region ‘externally’.
Important Note :
- excess of electrons implies negative charge
- A deficiency of electrons implies a positive charge
Text version for Flowchart:
Positive charges exert force on the negatively charged free electrons. Due to this attraction that the electrons feel, they get displaced towards the external positive charge. This causes one region to get an excess of electrons, i.e. negative charge, while the other has a deficiency of electrons, i.e., a positive charge. This is how charge separation happens in a conductor
These charges are ‘induced’ on the conductor due to the external charge. This phenomenon of separation of charges in a body by some external factor is called ‘Charge Induction’
2.2 Charge Induction in Non-Metals
As discussed, the basic difference between non-metal and metals is the absence of free electrons in case of non-metals.
Setup – Let’s consider the same condition. An non-metallic body has been placed in a region. Now, we bring a positive charge in vicinity of this body.
Important Note:
- Atom is made up of a positively charged nucleus and an negatively charged electron cloud surrounding it. In a neutral, undisturbed atom, the negative center and the positive center, both, coincide.
Text version of Flowchart:
Positive charges exert force on the negatively charged electron cloud in the atom.
Due to this attraction, the negative center gets slightly displaced towards the external positive charge.
This causes separation of the negative and positive centers of the atom. We now call this atom a dipole.
All the dipoles tend to align themselves such that the negative side is closer to the external positive charge.
This alignment in dipoles in a non-conducting body due to an external charge is called induction in non-conducting bodies or ‘Polarization’. The separation between positive and negative charges is very very small. So, usually, we ignore it in our problem solving, etc.
Special Note :
This is why a Charged body always attracts a Neutral body. We can also conclude that :
“Attractive force on neutral conducting body will be more due to any external charge”
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