Electric charges and fields


Question 1. Draw a diagram to show lines of force in a plane containing two equal point charges of opposite sign separated by a small distance. Giving reason, indicate on the diagram a point where a small positive charge experiences a force parallel to the line joining the two charges.

Solution. As shown in the above figure, electric field at any point P on the equatorial line is parallel to the line joining the two charges. So if a small positive charge is placed at such a point, it will experience a force parallel to the line join in the two charges.

Question 2. What is meant by the statement that the electric field of a point charge has spherical symmetry whereas that of an electric dipole is cylindrical symmetric?

Solution. The electric field due to a point charge q at distance r from it is given by

Question 3. An electric dipole free to move is placed in a uniform electric field. Explain along with diagram its motion when it is placed,

(a) Parallel to the field. (b) Perpendicular to the field.

Solution. (a) Since the line of action of the two forces passes through the same point, the net force and the net torque acting on the dipole is zero. So no motion is produced when a dipole is placed to the electric field.

Solution: The directions of the two dipole moments and their resultant are shown in the above figure.

Originally published at https://bdslearningapp.blogspot.com on December 5, 2020.

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