Read the following passage and answer the questions.
A student studies the charges on four very tiny plastic beads, P, Q, R and S. All four beads are neutral at the start. She charges each bead by rubbing it with a different material. A sensitive meter then gives the charge on each bead. Her readings are: P, \(+8.0\times10^{-19}\ \mathrm{C}\); Q, \(-4.8\times10^{-19}\ \mathrm{C}\); R, \(+3.2\times10^{-19}\ \mathrm{C}\); and S, \(-1.6\times10^{-19}\ \mathrm{C}\).
Next, she puts all four beads in a small closed box. The beads can touch one another inside the box, but no charge can enter or leave it. She also compares each reading with the magnitude of the charge on an electron, \(1.6\times10^{-19}\ \mathrm{C}\). Her teacher tells her that charged bodies in everyday experiments carry much larger charges, of a few microcoulombs.
The student takes a fresh neutral bead. She removes electrons from it a few at a time and measures its charge each time. She plots the charge \(q\) of the bead on the y-axis against the number \(n\) of electrons removed on the x-axis. Her points lie on
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → a straight line through the origin with slope \(e\)
A body becomes positively charged by losing electrons. When \( n \) electrons are removed, its charge is \( q=ne \). So \( q \) grows in equal steps of \( e \) as \( n \) grows.
Option (1) a straight line through the origin with slope \(e\) — Correct. \( q=ne \) has the form \( y=mx \). The points lie on a straight line through the origin, and the slope is \( q/n=e \).
Option (2) a straight line through the origin with slope \(1/e\) — Incorrect. A slope of \( 1/e \) would mean \( q=n/e \). The charge is the number of electrons multiplied by \( e \).
Option (3) a straight line parallel to the \(n\)-axis — Incorrect. A line parallel to the n-axis would mean the charge stays the same. Each electron removed adds the same amount of positive charge.
Option (4) a curve that rises more and more steeply — Incorrect. Each electron carries the same charge \( e \), so every step in \( q \) is equal. The line cannot bend.
NCERT (2026-27):
Electric Charge – “A body can thus be charged positively by losing some of its electrons.”
Quantisation of charge – “Thus the charge on any body is always an integral multiple of e and can be increased or decreased also in steps of e.”