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## Homework Statement

We have two conducting plates. One is moveable, the other is not moveable. The moveable has the charge of +1V. While the other plate has the charge 0V and is part of a enclosing envelopment. See fig:

http://tinypic.com/view.php?pic=wb2onm&s=6

But when we move the upper plate horizontaly shown in the figure below the capacitance gets lower.

http://tinypic.com/view.php?pic=4hcrbb&s=6

In the figure the E-field and potential is plotted. How am I to motivate why the capacitance gets lower?

## Homework Equations

From the relevant equations we got:

Q=CV (1)

and

[tex]V_{12}=\int{E\cdot{dl}} (2)[/tex]

[tex]C=\epsilon\frac{S}{d} (3)[/tex]

## The Attempt at a Solution

I tried to motivate that the E-field gets weaker because the distance is greater in the horizontal axis. Then i suppose that the value of V gets smaller when you calculate the potential between the metal plates by equation (2).

But this doesn't seem quite correct to me since the capacitance C is independent of V and Q. We see by equation 3 that the capacitance is dependent of the surface area S and the distance d.

But the surface is the same, the only thing that changes is the distance. But the vertical distance is still the same.

So how do i motivate that the value of the capacitance decreaces?