Two point changes q and –q are placed at a distance 2a apart. Calculate the

electric field at a point P situated at a distance r along the perpendicular
bisector of the line joining the charges. What is the field when r >> a?

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For points on the equatorial line

An equatorial line of a dipole is the line perpendicular to the axial line and passing through a point mid way between the charges.

Electric Field Intensity due to a Dipole at a Point lying on the Perpendicular Bisector of a Dipole


 

 

electric field intensity due to perpendicular bisector of dipole

 

Consider a dipole consisting of -q and +q separated by a distance 2a. Let P be a point Consider a point P on the equatorial line.

The resultant intensity is the vector sum of the intensities along PA and PB. EA and EB can be resolved into vertical and horizontal components. The vertical compents of EA and EB cancel each other as they are equal and oppositely directed. It is the horizontal components which add up to give the resultant field.

E = 2EA cos q

As 2qa = p

As a special case,

We find that at very far off points i.e., 2a < r.< r.

Electricity intensity at an axial point is twice the electric intensity on the equatorial line.

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