Electric Field due to a Dipole Notes | EduRev

Physics Class 12

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Class 12 : Electric Field due to a Dipole Notes | EduRev

The document Electric Field due to a Dipole Notes | EduRev is a part of the Class 12 Course Physics Class 12.
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WHAT IS AN ELECTRIC DIPOLE
An electric dipole is defined as a pair of equal and opposite charges separated by a distance. However, a continuous charge distribution can also be approximated as an electric dipole from a large distance. These dipoles are characterized by their dipole moment, a vector quantity defined as the charge multiplied by their separation and the direction of this vector quantity is from the -Ve charge to the +ve charge. The total charge corresponding to a dipole is always zero. As the positive and negative charge centers are separated by a finite distance, the electric field at a test point does not cancel out completely leading to a finite electric field. Similarly, we also get finite electric potential due to a dipole.

ELECTRIC FIELD DUE TO A DIPOLE
The electric field due to a pair of equal and opposite charges at any test point can be calculated using the Coulomb’s law and the superposition principle. Let the test point P be at a distance r from the center of the dipole. The distance between +q and -q is d. We have shown the situation in the diagram below.
Electric Field due to a Dipole Notes | EduRevIElectric Field due to a Dipole Notes | EduRev   anElectric Field due to a Dipole Notes | EduRev be the electric field at point P due to the positive and the negative charges separately then the total electric fielElectric Field due to a Dipole Notes | EduRev at Point P can be calculated by using the superposition principle.
Electric Field due to a Dipole Notes | EduRev

Please note that the directions oElectric Field due to a Dipole Notes | EduRev and Electric Field due to a Dipole Notes | EduRev are alonElectric Field due to a Dipole Notes | EduRev and Electric Field due to a Dipole Notes | EduRev respectively. This is the most general form of the electric field due to a dipole. However, we will express this vector in terms of radial and inclination vectors as shown in the diagram below.
Electric Field due to a Dipole Notes | EduRevIn order to calculate the electric field in the polar coordinate, we will use the expression of the electric potential due to an electric dipole which we have calculated earlier.
Electric Field due to a Dipole Notes | EduRev
Here p is the magnitude of the dipole moment and is given by qd

We can easily derive the electric field due to this dipole by calculating the negative gradient of this electric potential. In polar coordinate electric field will be independent of azimuthal (ϕ) coordinate.
Electric Field due to a Dipole Notes | EduRev
The resultant electric field at point P is
Electric Field due to a Dipole Notes | EduRev
As shown in the diagram, the resultant electric field makes an angle \alpha with the radial vector. Then
Electric Field due to a Dipole Notes | EduRev

ELECTRIC FIELD AT AN AXIAL POINT
Electric Field due to a Dipole Notes | EduRevIn this case, the test point P is on the axis of the dipole. Consequently θ= 0 or π. The electric field at point P is
Electric Field due to a Dipole Notes | EduRev


SIMPLIFIED DERIVATION
The electric field at point P due to the positive charge is
Electric Field due to a Dipole Notes | EduRev
Electric field at point P due to negative charge is
Electric Field due to a Dipole Notes | EduRev
Total electric field due to the dipole at axial point P is
Electric Field due to a Dipole Notes | EduRev
At a relatively large distance r>>d/2 and we can approximate the electric field as
Electric Field due to a Dipole Notes | EduRev

ELECTRIC FIELD AT AN EQUATORIAL POINT
Electric Field due to a Dipole Notes | EduRevIn this case, the test point P is on the perpendicular bisector of the dipole. Consequently θ= π/2. The electric field at point P is
Electric Field due to a Dipole Notes | EduRev

SIMPLIFIED DERIVATION
The electric field at point P due to positive charge is
Electric Field due to a Dipole Notes | EduRev
Electric field at point P due to negative charge is
Electric Field due to a Dipole Notes | EduRev
Total electric field due to the dipole at equatorial point P is
Electric Field due to a Dipole Notes | EduRev
At a relatively large distance r>>d/2 and we can approximate the electric field as
Electric Field due to a Dipole Notes | EduRev

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