Which of the following statements correctly explains/explain the existence of a positive force between two electric charges? 1. Both the charges are positive. 2. Both the charges are negative. 3. Both the charges are oppositely charged. Select the correct answer using the code given below.
- (a)1 only
- (b)2 only
- (c)1 and 2 only
- (d)1, 2 and 3
Correct — C, 1 and 2 only. A 'positive' force between two charges means a repulsive force, and by Coulomb's law like charges repel while unlike charges attract. When both charges are positive (statement 1) or both are negative (statement 2), the product of the charges is positive, so the force is repulsive — a positive force. When the charges are opposite (statement 3), the product is negative and the force is attractive, which counts as a negative force. So only statements 1 and 2 explain a positive (repulsive) force.
- (a)1 only — Two negative charges repel each other just as two positive charges do, so statement 2 is equally valid; the answer cannot be '1 only'.
- (b)2 only — Two positive charges repel just as two negative charges do, so statement 1 is also correct — not '2 only'.
- (d)1, 2 and 3 — Statement 3 (oppositely charged) gives an attractive force, which is a negative force, so it does not explain a positive (repulsive) force.
Coulomb's law gives the electrostatic force between two point charges as F = k·q₁q₂/r², acting along the line joining them. Like charges (both positive or both negative) repel, while unlike charges attract. By the usual sign convention a repulsive force is taken as positive and an attractive force as negative.
The key is to read 'positive force' as a repulsive force rather than as a force acting on a positive charge. A repulsion needs the charges to be alike, which is true both for two positive charges and for two negative charges — hence statements 1 and 2, but not the oppositely charged case.
- Coulomb's law: F = k·q₁q₂/r², directed along the line joining the charges.
- Like charges (both + or both −) repel; unlike charges attract.
- By convention a repulsive force is positive and an attractive force is negative.
- The force magnitude falls off as the inverse square of the separation r.
Only like charges give a repulsive (positive) force — statements 1 and 2, option (c).
- Reading 'positive force' as 'force on a positive charge' instead of a repulsive force.
- Forgetting that two negative charges repel just like two positive ones.
A statement-code item hinging on the sign convention — a 'positive force' means repulsion, which requires like charges.
No directly related past PYQ was found.
- practice — not a real PYQ
Two charges exert an attractive force on each other. This means the charges are
- (a)both positive
- (b)both negative
- (c)of opposite sign
- (d)both zero
Answer(c) of opposite sign — unlike charges attract.
- practice — not a real PYQ
If the distance between two point charges is doubled, the electrostatic force between them becomes
- (a)half
- (b)double
- (c)one-fourth
- (d)four times
Answer(c) one-fourth — the force varies as 1/r².