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NEET
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Physics
Chapter
Capacitance

NEET · Physics · Capacitance

Five capacitors are connected to form a Wheatstone bridge network...

Five capacitors are connected to form a Wheatstone bridge network between terminals AA and BB. The first branch between AA and BB consists of two capacitors in series having capacitances CC and 3C3C. The second branch between AA and BB consists of two capacitors in series having capacitances 5μF5 \mu\text{F} and 15μF15 \mu\text{F}. A central capacitor of 10μF10 \mu\text{F} connects the junction of the first branch to the junction of the second branch. If the potential difference across the 10μF10 \mu\text{F} capacitor is zero and the equivalent capacitance of the network between AA and BB is 6μF6 \mu\text{F}, the value of CC is :

Options

  1. A2μF2 \mu\text{F}
  2. B5μF5 \mu\text{F}
  3. C3μF3 \mu\text{F}
  4. D4μF4 \mu\text{F}

Correct answer

C. 3μF3 \mu\text{F}

Step-by-step solution

Since the potential difference across the 10μF10 \mu\text{F} capacitor is zero, the bridge is balanced and the central capacitor can be removed from the circuit.

The equivalent capacitance of the upper branch (series combination of CC and 3C3C) is:
Cupper=C×3CC+3C=3C4C_{\text{upper}} = \dfrac{C \times 3C}{C + 3C} = \dfrac{3C}{4}

The equivalent capacitance of the lower branch (series combination of 5μF5 \mu\text{F} and 15μF15 \mu\text{F}) is:
Clower=5×155+15=7520=154μFC_{\text{lower}} = \dfrac{5 \times 15}{5 + 15} = \dfrac{75}{20} = \dfrac{15}{4} \mu\text{F}

The total equivalent capacitance is the parallel combination of the upper and lower branches:
Ceq=Cupper+ClowerC_{\text{eq}} = C_{\text{upper}} + C_{\text{lower}}
6=3C4+1546 = \dfrac{3C}{4} + \dfrac{15}{4}
24=3C+1524 = 3C + 15
3C=9⇒C=3μF3C = 9 \Rightarrow C = 3 \mu\text{F}

Answer: 3μF3 \mu\text{F}
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