The figure shows two capacitors in series, the rigid central conducting section of length b being movable vertically. If the potential of the upper and lower plates are V1 and V2, respectively, then the potential of the rigid section is :
A
V1−(V1−V2)x(a−b)
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B
V1−(V2−V1)x(a−b)
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C
V1−(V1−V2)x(a+b)
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D
V1−(V2−V1)x(a+b)
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Solution
The correct option is AV1−(V1−V2)x(a−b) The circuit is equivalent to two capacitors in series. C1=ε0Ax C2=ε0Aa−b−x
Now potential will be distributed in these capacitors. We can reduce this structure in the following circuit. V1−V=(V1−V2)C2C1+C2 V1−V=(V1−V2)ε0Aa−b−xε0Ax+ε0Aa−b−x=(V1−V2)x(a−b)