[Moved]some basic question on capacitance

[uday mehta]

1. what will happen if I insert conductive plate between two plates of a capacitor ?
2. what will happen if I insert a plate which is connected to ground between two plates of capacitor?
3. what will happen if I insert a plate which is connected to supply voltage between two plates of capacitor?

 

[kemiyun]

Re: some basic question on capacitance

You'll have two capacitors, which share a common node.

You'll have two capacitors, which share a common node that is connected to ground.

You'll have two capacitors, which share a common node that is connected to supply.

Assuming the other nodes are floating, you can do whatever you want with this configuration.

 

[betwixt]

Re: some basic question on capacitance

If you insert a conductive plate between the plates of a capacitor it becomes a resistor and capacitor in parallel. Depending on how conductive the middle layer is, the result could be anything from a complete short circuit to a slight discharge path ( a 'leaky' capacitor).

Brian.

 

[uday mehta]

If I want to vanish the capacitance without shorting the plates.
what should I do?
actually in my design I have two parallel plates for different purpose. but they are acting as a capacitor i.e. i am facing a huge coupling. I want that they should not act as capacitor. what is the solution?

 

[kemiyun]

There is no solution, you can't "vanish" that capacitance. That is the physical phenomena that creates capacitors in the first place. You can put them far away from each other, change the dielectric material somehow, or change the area of the plates that are causing the highest amount of coupling.

Also, Brian, considering the node that you inserted is floating, where would it discharge to? Can you elaborate more, I'd rather not misguide someone, I just thought if everything is floating there would be conductor-dielectric-conductor-dielectric-conductor kind of thing. That's why I said what I said.

 

[uday mehta]

even after inserting a ground plate between two plates, signal on first plate effect the second plate?

 

[kemiyun]

Yeah the thing is its effect on the second signal would be reduced, if you put ground or vdd in between. Because the signal will couple to these DC voltages instead of the other signal line. But by doing this you're actually increasing the total capacitor that is loading that node, it's just decoupled to ground or vdd and not coupled to the other signal.

 

[betwixt]

Also, Brian, considering the node that you inserted is floating, where would it discharge to? Can you elaborate more, I'd rather not misguide someone, I just thought if everything is floating there would be conductor-dielectric-conductor-dielectric-conductor kind of thing. That's why I said what I said.

A conductive dielectric would leak charge between the original plates in the same way connecting a resistor across it would. If you mean a conductive center plate is added but it doesn't touch the existing plates, in other words it is a middle but floating plate, you have simply created two capacitors in series and the charge across them for a given vlotage will be proportonal to their relative capacitive values.

Brian.

 

[kemiyun]

Ah, I see. I just assumed that the original question meant putting another conductor in between and leaving it floating, not a connection from one side to the other. Thanks.