A polythene piece rubbed with wool is found to have a negative charge of \( 8\times10^{-10}\,\mathrm{C} \). What is the number of electrons transferred?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 5\times10^{9} \); wool to polythene
In charging by rubbing, electrons pass from one body to the other; the body that gains electrons becomes negative. Since charge is quantised, \( q = ne \).
\( \displaystyle n = \frac{q}{e} = \frac{8\times10^{-10}\,\mathrm{C}}{1.6\times10^{-19}\,\mathrm{C}} = 5\times10^{9} \)
The polythene ends up negative, so it has gained these electrons. They were transferred from wool to polythene, and the wool is left with an equal positive charge.
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
