IIT JEE , AIEEE Forum - Physics , Electricity

rooney

Ok Let me explain using a question.

Suppose there are 2 capacitors A and B with capacitance C₁ and C₂(C₁>C₂).Both are charged to voltage V and the same charged plates are connected to each other . This means that +ve plate of A is in touch with +ve plate of B AND -ve plate of A is in touch with -ve plate of B. Now we have to find the final charge on both the plates.

Let final charge ( in steady state ) on A be Q₁ and on B be Q₂.

Firstly, since net P.D. across a circuit is 0. From formula V=Q/C , we have
V₁ + V₂ = 0
Q₁/C₁ - Q₂/C₂ = 0 ..........(going anticlockwise)....[1]

Now the +ve plate of A and the positive plate of B are an isolated system. So, initial and final sum of charges on both these plates will be same.
So, C₁V + C₂V = Q₁ + Q₂

Only Q₁ and Q₂ are unknown and you have two equations, you can get their value. IF the final polarity of B plate comes out to be opposite, you will get value of Q₂ as negative.

Hope this makes things clearer

Regards,
Rooney

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