Inside Story

# ELECTRIC DIPOLE AND ELECTRIC DIPOLE MOMENT

### INTRODUCTION

Charges are present everywhere, Charges are present in all those things which have mass. There is a charge in your plastic pen and also in the pages of your notebook. Have you ever in your childhood rubbed your pen with your hair and taken it to small pieces of paper, if so, you must have noticed that the pen attracts those pieces of paper.

What happens with the pen?, actually when we rub plastic pen with our hairs then some electrons transfer to the hairs from the pen and this make the pen positively charged and hairs negatively charged. Here both pen and hairs become a electric dipole. How? We will discuss further about this.

We know that when we bring two opposite charged particles (having different magnitude) close to each other then they start attracting to each other.

But –

In this section we will discuss in detail about a special case in which two opposite charged particles with same magnitude are kept at distance d. This special case is called the electric dipole, which plays a vital role in the electrostatic physics.

So stay connected with us till end…

## WHAT IS ELECTRIC DIPOLE?

*Electric dipole is a pairs of charge particles having equal and opposite charges and which are seperated by the very short distance.*

The mid point of the electric dipole is called the centre of the dipole.

We had talked in introduction that the pen and hairs both become a pairs of electric dipole. How? Actually When we rub our plastic pen with our hairs then some electrons are ejected from the pen and get entered to the hairs.

But it becomes a electric dipole because the numbers of loosen electrons by the pen is equal to the numbers of gained electrons by the hairs. Due to this both show equal and opposite charges ( if pen shows +q charge then the hairs will show -q charge) and the distance between them is very small.

And a electric dipole is what ? A electric dipole is a pairs of equal and opposite charges, which is seperated by the some small distance d.

## WHAT IS ELECTRIC DIPOLE MOMENT

*Electric Dipole moment is the mathematical interpretation of the strength of the electric dipole.*Electric dipole moment (p) is a vector quantity and it’s direction is always from negative to positive.

The strength of the electric dipole is given by the product of the Charge (q) and their separation distance (d) and this strength is called electric dipole moment.

Mathematically it is given as –

p = q × 2r or |p| = q(2r)

The SI unit of electric dipole moment is coulomb-metre ( C-m). But other unit of electric dipole moment is debye which is used in atomic physics and chemistry.

## PROPERTIES OF ELECTRIC DIPOLE

Some properties of electric dipole is given below –

1). Electric dipole is a pair of equal and opposite electric charges, which is seperated by a very small distance.

2). Electric dipole is analogous to the magnetic dipole. The electric field lines of electric dipole is same as the magnetic field lines of a bar magnet.

3). If charge q gets larger and larger and the separation distance (2r) gets smaller and smaller, keeping the product |p| = q×2r = constant, then we get what is called a ideal dipole or a point dipole.

4). The ideal dipole is the smallest dipole having almost zero size.

5). When an electric dipole is kept in a external electric field region then the dipole moment makes a angle θ with the direction of the electric field. This make electric dipole to experience a Torque.

Watch this video for more reference.

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