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A capacitor \(C_1=6 \mu \mathrm{~F}\), initially charged with a cell of emf 5 V is disconnected and connected to another…

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A capacitor \(C_1=6 \mu \mathrm{~F}\), initially charged with a cell of emf 5 V is disconnected and connected to another capacitor \(C_2=12 \mu \mathrm{~F}\) which is initially neutral. The charges on \(C_1\) and \(C_2\) after connection are

(Shift - II Memory Based)

a

\(0 \mu \mathrm{C}, 30 \mu \mathrm{C}\)

b

\(10 \mu \mathrm{C}, 20 \mu \mathrm{C}\)

c

\(20 \mu \mathrm{C}, 10 \mu \mathrm{C}\)

d

\(30 \mu \mathrm{C}, 0 \mu \mathrm{C}\)

✓ Correct answer: b)

\(10 \mu \mathrm{C}, 20 \mu \mathrm{C}\)

ExplanationStep 1: Initial Charge on \({C}_{1}\)​

The charge on a capacitor is given by:

\(Q=CV\)

Given:

  • \({C}_{1}=6\mu F\)
  • \(V=5V\)

\({Q}_{1}=(6\times 1{0}^{−6}F)\times (5V)=30\mu C\)

Since \({C}_{2}\)​ is initially uncharged, its initial charge is:

\({Q}_{2}=0\mu C\)

Step 2: Charge Conservation

When the two capacitors are connected, charge redistributes while maintaining charge conservation:

\({Q}_{\text{total}}={Q}_{1}+{Q}_{2}=30\mu C+0=30\mu C\)

Step 3: Common Voltage after Connection

Since the capacitors are connected in parallel, they share a common voltage \({V}_{f}\):

\({V}_{f}=\frac{{Q}_{\text{total}}}{{C}_{1}+{C}_{2}}\)

\({V}_{f}=\frac{30\mu C}{(6+12)\mu F}\)V

​ \({V}_{f}=\frac{30}{18}V=\frac{5}{3}V\)

Step 4: Finding Final Charges

Using \(Q=CV\)

  1. Final charge on \({C}_{1}\):

\({Q}_{1}^{′}={C}_{1}{V}_{f}=(6\mu F)\times \frac{5}{3}V\)

\({Q}_{1}^{′}=10\mu C\)

  1. Final charge on \({C}_{2}\):

\({Q}_{2}^{′}={C}_{2}{V}_{f}=(12\mu F)\times \frac{5}{3}V\)

\({Q}_{2}^{′}=20\mu C\)

Step 5: Selecting the Correct Option

The charges on \({C}_{1}\)​ and \({C}_{2}\)​ after connection are:

\(B\ 10\mu C,20\mu C\)

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