Two positive point charges (at ) and (at ) are apart in air

PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

Two positive point charges

+3\,\mu\text{C}

(at

P

) and

+12\,\mu\text{C}

(at

Q

) are

30\,\text{cm}

apart in air. A very small positive test charge is placed at the point on

PQ

where the net electric force on it is zero. If the test charge is now displaced slightly towards

P

and released, what will be the direction of the net force acting on it? (a) Towards

P

, pushing it further away from the equilibrium point (b) Zero; the test charge stays at the displaced position (c) Towards

Q

, pulling it back to the equilibrium point (d) Perpendicular to

PQ

, causing it to curve around the equilibrium point