PYQ NEET- Concept Of Charge And Coulom'S Law

• NEET 2019: A charge q is placed at the centre of the line joining two equal charges Q. The system of these three charges will be in equilibrium if q is equal to:

(A) -Q/4 (B) Q/4 (C) Q/2 (D) Q

The answer is: (B)

Explanation:

The net force on charge q is zero. So,

F1 + F2 = 0

KqQ/r^2 + Kq(-q)/r^2 = 0

q^2 = Q^2/4

q = Q/4

• NEET 2018: Two charges of magnitude +q and -q are placed at a distance d apart. At what distance from the positive charge, the electric field will be zero?

The answer is: (D)

Explanation:

The electric field due to a charge q at a distance r is given by

E = k q/r^2

For the electric field to be zero, the distance from the positive charge must be