A negative point charge is fixed in space. A small negative charge is projected from a point B towards a point A, which is closer to the fixed charge. Only the electrostatic force acts on the moving charge. As it goes from B to A, its kinetic energy
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → decreases, because its potential energy increases
Around a negative point charge the potential is negative. It is more negative closer to the charge, so \( V_A\lt V_B \). For a charge \( q \), the change in potential energy from B to A is \( q(V_A-V_B) \). Both factors are negative here, so the change is positive.
Option (1) increases, because it moves to a point of lower potential — Incorrect. A is at a lower potential. For a negative charge, a lower potential means a higher potential energy, so the kinetic energy goes down.
Option (2) decreases, because its potential energy increases — Correct. The fixed charge repels the moving charge and slows it down. Its potential energy rises and its kinetic energy falls by the same amount.
Option (3) stays the same, because the electrostatic force is conservative — Incorrect. A conservative force keeps the sum of kinetic and potential energy fixed. Kinetic energy alone can still change.
Option (4) increases, because the electrostatic force does positive work on it — Incorrect. The force on the moving charge points away from the fixed charge, against the motion. So the force does negative work.
NCERT (2026-27):
Example 2.3 – “… Also VB is less negative than VA . …”
Example 2.3 – “(e) Due to force of repulsion on the negative charge, velocity decreases and hence the kinetic energy decreases in going from B to A.”