Question

For the configuration of capacitors shown, both switches are closed simultaneously. After equilibrium is established, what is charge on the top plate of the $5\mu F$ capacitor?

• A. $10\mu C$
• B. $90\mu C$
• C. $100\mu C$
• D. None of these

Answer 1

The correct option is A $10\mu C$

Applying KVL,
after connection let charge q flow through circuit as shown .

Now apply KVL in loop ( moving anticlockwise and taking potential drop as +ve)
$\frac{100-q}{5\times {10}^{-6}F}+\frac{50-q}{20\times {10}^{-6}F}=0$
$\Rightarrow 4(100-q)+(50-q)=0$
$\Rightarrow q=90\times {10}^{-6}C$
So, charge on top plate of $5\mu C=(100-q)=(100-90)\mu C$
$=10\mu C$
Hence, correct option is (C).