# Homework Help: Dielectric between plates.

1. Mar 29, 2017

### Arman777

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
I couldnt find the V(x).I dont know ho to write the equation.I think that it will be constant cause potential betwwen two plates should be constant... ?

2. Mar 29, 2017

### cnh1995

What is the energy in the capacitor as a function of x?
In other words, what is the capacitance as a function of x?
How is force related to this energy?

3. Mar 29, 2017

### Arman777

$C_{eq}=(K+1)ε_0 \frac {xb} {d}$ ? or maybe
$C=Kε_0 \frac {xb} {d}$

4. Mar 29, 2017

### cnh1995

I don't know the exact expression as I myself haven't worked it out yet, but check the answer at x=0. Is the capacitance zero at x=0?

5. Mar 29, 2017

### Arman777

Yeah its

6. Mar 29, 2017

### cnh1995

No, it isn't.
What is the capacitance for x=0?

7. Mar 29, 2017

### Arman777

Theres no area when x=0

8. Mar 29, 2017

### cnh1995

How is this possible? Which area is considered for calculation of capacitance?

9. Mar 29, 2017

### Arman777

You are taking a-x I am just x

10. Mar 29, 2017

### cnh1995

But that doesn't make the total capacitance zero. You need to draw the equivalent circuit and find the total capacitance as a function of x.

11. Mar 29, 2017

### Arman777

I didnt understand

12. Mar 29, 2017

### cnh1995

What is the dielectric between the plates before the new dielectric (with constant k) is inserted?
What is the capacitance when the new dielectric is not inserted at all?