Question

The two charges $+Q$ and $-4Q$ are kept at some distance on the scale. The points $A$ to $E$ are marked as shown in figure. The net electric field is zero nearest to which point?

• A. A
• B. B
• C. C
• D. D
• E. E

Answer 1

The correct option is A A

The electric field is defined as the force per unit charge acting on a positive charge. If we place a small positive charge at point A to test the electric field, it would be repelled from +Q and attracted by -4 Q. The electric force is proportional to the product of the charges and inversely proportional to the square of the distance between the charges (Coulomb's law), and since the negative charge is four times greater than +Q the positive test charge must be farther from -4 Q than from +Q for the forces from each to cancel each other out and produce a net electric field of zero at point A.