Read the following passage and answer the questions.
Coulomb used a torsion balance to study the force between two small charged metal spheres. A torsion balance is a very sensitive device for measuring small forces. The spheres were small compared with the distance between them, so they could be treated as point charges. At the start, Coulomb did not know the charge on either sphere.
To change a charge in a known way, he touched a charged sphere with an identical uncharged sphere. Then he took the second sphere away. He repeated this step to get smaller and smaller charges. In one set of readings, he kept the charges fixed and changed the distance between the spheres. In another set, he kept the distance fixed and changed the charges in pairs. By comparing all the readings, he arrived at a simple law for the force between two point charges.
Coulomb got smaller charges by touching a charged sphere with an identical uncharged sphere. This method assumes that electric charge is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → additive and conserved
When the two identical spheres touch, the charge spreads equally over them, so each gets half. This works only if the two halves together make up the charge at the start.
Option (1) quantised in units of \(e\) — Incorrect. The method does not use the size of \( e \). At the large charges Coulomb used, the steps of \( e \) are far too small to matter.
Option (2) a vector quantity — Incorrect. Charge has no direction. It is a scalar, and the two halves add like ordinary numbers.
Option (3) created when the spheres touch — Incorrect. No new charge is created on contact. The charge already present is only shared.
Option (4) additive and conserved — Correct. Two charges of \( q/2 \) add to give \( q \) (additivity), and the total \( q \) does not change on sharing (conservation).
NCERT (2026-27):
Coulomb’s Law – “Implicit in this is the assumption of additivity of charges and conservation: two charges (q/2 each) add up to make a total charge q.”