Question
Question: Three identical, parallel conducting plates A, B and C are placed as shown. Switches S<sub>1</sub> a...
Three identical, parallel conducting plates A, B and C are placed as shown. Switches S1 and S2 are open, and can connect A and C to earth when closed. +Q charge is given to B. Then:
Three identical, parallel conducting plates A, B and C are placed as shown. Switches S1 and S2 are open, and can connect A and C to earth when closed. +Q charge is given to B. Then:
If S1 is closed with S2 open, a charge of amount Q will pass through S1
If S2 is closed with S1 open, a charge of amount Q will pass through S2
If S1 and S2 are closed together, a charge of amount Q/3 will pass through S1 and a charge of amount 2Q/3 will pass through S2
All of the above statements are incorrect
All of the above statements are incorrect
Solution
When either A or C is earthed (but not both together), a parallel-plate capacitor is formed with B, with ±Q charges on the inner surfaces. [The other plate, which is not earthed, plays no role]. Hence, charge of amount +Q flows to earth.
When both are earthed together A and C effectively become connected. The plates now form two capacitors in parallel with capacitances in the ratio 1:2 and hence, share charges Q in the same ratio.