Q74 / 120 · NEET 2012 (Mains) · Physics
Two metallic spheres of radii $1 \mathrm{~cm}$ and $3 \mathrm{~cm}$ are given charges of $-1 \times 10^{-2} \mathrm{C}$ and $5 \times 10^{-2} \mathrm{C}$, respectively. If these are connected by a conducting wire, the final charge on the bigger sphere is
- A$2 \times 10^{-2} \mathrm{C}$
- Correct answerB$3 \times 10^{-2} \mathrm{C}$
- C$4 \times 10^{-2} \mathrm{C}$
- D$1 \times 10^{-2} \mathrm{C}$
Solution
Charge flows from high potential to low potential
$$
\begin{aligned}
\frac{K Q_1}{3} & =\frac{K Q_2}{1} \\
Q_1 & =3 Q_2
\end{aligned}
$$
Also
$$
\begin{aligned}
Q_1+Q_2 & =4 \times 10^{-2} \\
4 Q_2 & =4 \times 10^{-2}
\end{aligned}
$$
$Q_2=10^{-2}$
and $\quad Q_1=3 \times 10^{-2} \mathrm{C}$
Hence, the correct answer is option: 'B'.