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Question: Answered & Verified by Expert
A $1 \mu \mathrm{F}$ capacitor $C$ is connected to a battery of $10 \mathrm{V}$ through a resistance 1 Mega Ohm. The voltage across $C$ after 1 s is approximately
PhysicsCurrent ElectricityWBJEEWBJEE 2016
Options:
  • A $5.6 \mathrm{V}$
  • B $7.8 \mathrm{V}$
  • C $6.3 \mathrm{V}$
  • D $10 \mathrm{V}$
Solution:
1954 Upvotes Verified Answer
The correct answer is: $6.3 \mathrm{V}$


The time constant of the circuit
Here,
$$
\begin{aligned}
\tau &=C \cdot R \\
C &=1 \mu F=1 \times 10^{-6}
\end{aligned}
$$
$$
\begin{array}{l}
R=1 \mathrm{M\Omega}=1 \times 10^{6} \Omega \\
\tau=1 \times 10^{-6} \times 1 \times 10^{6}=1 \mathrm{s}
\end{array}
$$
We know that in one (1) time constant $63 \%$ charging is done. $\therefore \quad \frac{63}{100} \times q_{\max }$
$=\frac{63}{100} \times 1 \times 10^{-6} \times 10$
$=\frac{63}{100} \times 1 \mu \mathrm{F} \times 10=6.3 \mu \mathrm{C}$
$V=\frac{\mathrm{q}}{\mathrm{C}}=\frac{6.3 \times 10^{-6} \mathrm{C}}{1 \times 10^{-6} \mathrm{F}}=6.3 \mathrm{V}$

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