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Q.Calculate the equivalent capacitance between the points A and B in the following Figure:

a row of four capacitors 2, 3, 5 and 10 microfarad with bypass wires between A and B — Class 12 Physics electrostatics question
Figure
Haryana BsehBSEH Intermediate Board 2018Subjective· 2mImportance★★★★★
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The plain conducting wires short A to Q and P to R, collapsing C1, C2, C3 into one parallel combination (10 μF), which is then in series with C4 (10 μF), giving 5 μF overall.

A plain connecting wire has no capacitance and no resistance, so any two nodes joined directly by such a wire are forced to the same potential — they become electrically one node.

  • The wire from A to Q makes A and Q the same node.
  • The wire from P to R makes P and R the same node.

Now re-examine each capacitor's terminals using these identifications:

  • C1C_1 (2 μF) is between A and P.
  • C2C_2 (3 μF) is between P and Q — but Q = A, so C2C_2 is also between P and A.
  • C3C_3 (5 μF) is between Q and R — but Q = A and R = P, so C3C_3 is also between A and P.

So C1C_1, C2C_2, and C3C_3 all sit between the same pair of nodes (A and P), i.e. they are in parallel: …

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