Electric Dipole

Electric Dipole moment is the measure of the polarity of the system. It is the separation of positive charge and a negative charge by a distance. The SI unit of electric dipole moment is Coulomb-meter. The simplest example is a pair electric charge of two opposite sign and equal magnitude separated by distance.

What is Electric Dipole?

Suppose there are two charges of equal magnitude ‘q’, separated by a distance ‘d’. Let the first charge be negative and the second charge be positive. This combination can be called as an electric dipole. Therefore, we can say that an electric dipole is created by the combination of equal and opposite charges by a separation of a certain distance.

Electric Dipole

Now, the electric dipole moment for this pair of equal and opposite charges is equal to the magnitude of the charges multiplied by the distance between them.

Magnitude of Electric Dipole Moment

The magnitude of electric dipole moment can be written as:

\( \overrightarrow{p} \) = \( q \overrightarrow {d} \)

Direction of Electric Dipole Moment

The electric dipole moment is a vector quantity; it has a defined direction which is from the negative charge to the positive charge. Though, it is important to remember that this convention of direction is only followed in Physics. In Chemistry, the convention is taken to be opposite i.e. from positive to negative. The line along the direction of an electric dipole is called the axis of the dipole.

 

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Electric potential due to a Dipole (V)

Suppose there are two charges –q, placed at A, and +q placed a B, separated by a distance d, forming a dipole. Suppose the midpoint of AB is O.

The Electric potential due to a dipole at any point P, such that OP = r will be:

V = \(\frac{1}{4\pi \epsilon } \frac{p cos \theta }{r^{2}}\)

Case 1: If θ = 90°

Electric potential = V = 0 

Case 2: If θ = 0°

Electric potential = V = \(\frac{1}{4\pi \epsilon } \frac{p }{r^{2}}\) 

Frequently Asked Questions on Electric Dipole

What is the net force acting on a dipole placed in a uniform electric field?

The forces on the two charges constituting dipole are equal and opposite. Hence the net force is zero.

What is the SI unit of dipole moment?

The SI unit of dipole moment is Coulomb.meter

When is the torque on a dipole is maximum?

When the axis of the dipole is perpendicular to the field.

When is the torque on a dipole is minimum?

When the axis of the dipole is parallel to the field.

When an electric dipole is in stable equilibrium in an electric field?

When dipole moment is parallel to the electric field.

What is the electric dipole moment?

It is the measure of the strength of electric dipole. Its magnitude is equal to the product of the magnitude of any one charge and the distance between them.

Give an example for the electric dipole?

A pair electric charge of two opposite sign and equal magnitude separated by a distance.

Give the expression for the magnitude of an electric dipole?

p = 2qa

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