When a glass rod is rubbed with a silk cloth and both get charged, which of the following conservation laws does NOT hold?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → None of the above
Rubbing does not create charge. It only transfers electrons from the glass rod to the silk. So the rod becomes positive and the silk equally negative.
Option (1) Conservation of charge — Holds. The charge gained by the silk equals the charge lost by the rod, so the total charge of the rod and silk stays zero.
Option (2) Conservation of energy — Holds. The work done in rubbing appears as heat and as the electrical energy of the separated charges. No energy is created or lost.
Option (3) Conservation of angular momentum — Holds. Rubbing and the transfer of electrons act through forces inside the system of rod, cloth and hand. These internal forces do not change its total angular momentum.
Option (4) None of the above — Correct. Charge, energy and angular momentum are all conserved during the charging, so none of the listed laws fails.
NCERT (2026-27):
Charge is Conserved – “We have already hinted to the fact that when bodies are charged by rubbing, there is transfer of electrons from one body to the other; no new charges are either created or destroyed. A picture of particles of electric charge enables us to understand the idea of conservation of charge. When we rub two bodies, what one body gains in charge the other body loses.”