The SI unit of polarisation is______.

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Cm-2

Coulomb

Ampere

Volt

answer is A.

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Detailed Solution

Concept: In order to find the unit of polarisation, we first need to understand what the term "Electric Polarisation" means.
"Separation of positive charge from that of negative charges in the material on the application of the electric field to the material is defined as Electric Polarization."
It's basically the dipole moment per unit volume of the material.
As we know electric polarization is electric dipole moment per unit volume.
Now the dipole moment is defined as the product of charges into distance between them.
Therefore, the SI unit of dipole moment
= SI unit of charge

\times

SI unit of distance
Now we know that the SI unit of charge is coulomb (C) and the SI unit distance is meter(m).
So, the SI unit of the dipole moment is C $times$ m, that is Cm.
Similarly,
The SI unit of Electric Polarisation will be the SI unit of dipole moment divided by the SI unit of volume.
And we know that the SI unit of volume is cubic metres or m3.
The unit of Polarisation (P) is given as coulomb per square metre Cm-2 . Coulomb metre Cm is used to denote the dipole moment.

P = \frac{q}{A}

Where P is polarisation, q is a charge, A is area. We know that unit of q (charge) is Coulomb © and the unit of area is m2
Putting values in above equation we get