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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Capacitors

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Capacitors

Determine the equivalent capacitance between points A and B for the...

Determine the equivalent capacitance between points AA and BB for the infinite ladder circuit illustrated in the figure.
Determine the equivalent capacitance between points A and B for the infinite ladder circuit illustrated in the figure.

Options

  1. A2 μF2\ \mu\text{F}
  2. B1 μF1\ \mu\text{F}
  3. C0.5 μF0.5\ \mu\text{F}
  4. D3 μF3\ \mu\text{F}

Correct answer

A. 2 μF2\ \mu\text{F}

Step-by-step solution

Let the equivalent capacitance between points AA and BB be CeqC_{eq}.

Because the ladder is infinite, the circuit to the right of the first 2 μF2\ \mu\text{F} capacitor is identical to the entire circuit and thus has an equivalent capacitance of CeqC_{eq}.

The circuit can be simplified to a 1 μF1\ \mu\text{F} capacitor in parallel with the series combination of a 2 μF2\ \mu\text{F} capacitor and CeqC_{eq}.

The equivalent capacitance is given by:
Ceq=1+2⋅Ceq2+CeqC_{eq} = 1 + \dfrac{2 \cdot C_{eq}}{2 + C_{eq}}

Multiplying both sides by (2+Ceq)(2 + C_{eq}):
Ceq(2+Ceq)=1(2+Ceq)+2CeqC_{eq}(2 + C_{eq}) = 1(2 + C_{eq}) + 2C_{eq}

2Ceq+Ceq2=2+3Ceq2C_{eq} + C_{eq}^2 = 2 + 3C_{eq}

Ceq2−Ceq−2=0C_{eq}^2 - C_{eq} - 2 = 0

Factoring the quadratic equation:
(Ceq−2)(Ceq+1)=0(C_{eq} - 2)(C_{eq} + 1) = 0

Since capacitance must be positive, we discard Ceq=−1 μFC_{eq} = -1\ \mu\text{F}.

Therefore, Ceq=2 μFC_{eq} = 2\ \mu\text{F}.

Answer: 2 μF2\ \mu\text{F}
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