Capacitance of four metal plates

AI Thread Summary
The discussion focuses on calculating the equivalent capacitance between two points, A and B, in a system of four identical parallel metal plates connected by a wire. The plates are identified as nodes A, B, and C, with capacitance existing between each pair of nodes. Participants emphasize the importance of recognizing the three capacitors formed by the plates and understanding their connections. A suggestion is made to assign charges to the plates to clarify their potential differences and facilitate the calculation. The conversation aims to guide the original poster toward a correct solution by visualizing the arrangement and interactions of the capacitors.
Patrikp
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Homework Statement


Four identical parallel metal plates with area $$S$$ and distance between each two $$d$$ are located in air. The external plates are connected by wire. What is the equivalent capacitance between A and B?
This is problem from Irodov.

Homework Equations


$$q=UC$$[/B]

The Attempt at a Solution


Plates 1 and 4 are always on same potential which I am not sure how to use.
I tried to simplify as on the picture but that turns out to be wrong(why?).

[/B]
 

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As I see it there are three nodes, A, B and C (the wire connecting the outer plates 1 and 4).

Draw the three nodes on paper. There is capacitance between...

A and B
A and C
B and C
 
CWatters said:
As I see it there are three nodes, A, B and C (the wire connecting the outer plates 1 and 4).

Draw the three nodes on paper. There is capacitance between...

A and B
A and C
B and C
Can you explain how did you get that? Thanks
 
You have to recognize the 3 capacitors, its easier if you number them, say capacitor plate 1,2,3 and 4 , so the 3 capacitors are (12),(23) and (34), now try figuring out the the arrangement of these capacitors, by considering which are connected and which are not.
Patrikp said:
Can you explain how did you get that?
If you want to know how to recognize the 3 capacitors try giving the plates charges, imagine A is the +ve terminal and see which all plates should have +ve and which -ve, once you figure that out, i think you'll be able to get the answer.
 
Patrikp said:
Can you explain how did you get that? Thanks

Try..

image.jpg


PS the colours don't mean anything they are just to highlight the three nodes.
 
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