Class 12th Physics 2017 Set1 Delhi Board Paper Solution
Derive the expression for electric field at a point on the euqatorial line of an electric dipole.
Electric field at a point on the equatorial line of an electric dipole.
Consider an electric dipole consisting of two point charges + q and −q separated by a small distance AB = 2l with centre at O and dipole moment, p q = (2l) as shown in the figure.
Resultant electric field intensity at the point Q
On resolving EA and EB into two rectangular components, the vectors EA sinθ and EB sinθ are equal in magnitude and opposite to each other and hence, cancel out.
The vectors EA cosθ and EB cosθ are acting along the same direction and hence, add up.
∴EQ = EA cos + EB cos θ = 2EA cosθ
The direction of E is along QE || BA, i.e. opposite to AB. In vector form, we can rewrite as
Obviously, EQ is in a direction opposite to the direction of p
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