Question

Two fixed charges $4Q$ (positive) and $-Q$ (negative) are located at A and B, the distance AB being $3m$. Then:

• A. the point p where the resultant field due to both is zero is on AB outside AB.
• B. the point p where the resultant field due to both is zero is on AB inside AB
• C. if a positive charge is placed at p and displaced slightly along AB it will execute oscillations.
• D. if a negative charge is placed at p and displaced slightly along AB it will execute oscillations.

Answer 1

Answer: (A), (D)

The correct options are
A the point p where the resultant field due to both is zero is on AB outside AB.
D if a negative charge is placed at p and displaced slightly along AB it will execute oscillations.

(A) electric field due to positive charge is away from it and electric field due to negative charge is towards it so there cannot be a point on AB where electric field can be zero
(D) negative charge will experience a repulsion force due to $-ve$ charge and attraction force due to $+ve$ charge, so if pushed away from charges then a net attractive force and if pushed towards AB then a net repulsive force will be there so there will be oscillations