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Capacitance

NEET · Physics · Capacitance

In a circuit, a 20\ V battery is connected in series with a 2\...

In a circuit, a 20 V20\ \text{V} battery is connected in series with a 2 Ω2\ \Omega resistor. The circuit then splits into two parallel branches: the first branch contains a 3 Ω3\ \Omega resistor, and the second branch contains a 4 Ω4\ \Omega resistor in series with a 5 μF5\ \mu\text{F} capacitor. What is the charge stored on the capacitor at steady state?

Options

  1. A100 μC100\ \mu\text{C}
  2. B80 μC80\ \mu\text{C}
  3. C60013 μC\dfrac{600}{13}\ \mu\text{C}
  4. D60 μC60\ \mu\text{C}

Correct answer

D. 60 μC60\ \mu\text{C}

Step-by-step solution

At steady state, the capacitor is fully charged and acts as an open circuit, so no current flows through the branch containing the 4 Ω4\ \Omega resistor and the 5 μF5\ \mu\text{F} capacitor.

The steady-state current flows only through the 2 Ω2\ \Omega and 3 Ω3\ \Omega resistors, which are effectively in series.

The current in the circuit is:
I=VReq=202+3=4 AI = \dfrac{V}{R_{\text{eq}}} = \dfrac{20}{2 + 3} = 4\ \text{A}

The potential difference across the parallel section is the voltage drop across the 3 Ω3\ \Omega resistor:
Vp=I×3=4×3=12 VV_{p} = I \times 3 = 4 \times 3 = 12\ \text{V}

Since there is no current in the 4 Ω4\ \Omega resistor, there is no voltage drop across it. The potential difference across the capacitor is equal to the potential difference across the parallel section, which is 12 V12\ \text{V}.

The charge stored on the capacitor is:
Q=CV=5 μF×12 V=60 μCQ = CV = 5\ \mu\text{F} \times 12\ \text{V} = 60\ \mu\text{C}

Answer: 60 μC60\ \mu\text{C}
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