# Solving for distance between plates, diameter of a capacitor

1. Mar 4, 2015

### PhysicsMan999

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

1. A 5.02 pF air-filled capacitor with circular parallel plates is to be used in a circuit where it will be subjected to potentials of up to 95 V. The electric field between the plates is to be no greater than 1.40×104 N/C. As an electrical engineer for Live-Wire Electronics, your task is to design the capacitor. What is its size? Enter the diameter and the separation of the plates.
2. Relevant equations
C=kEA/d
E=V/d
A=pir^2

3. The attempt at a solution
I used E=V/d to try and find the distance, then plugged that into the capacitance equation to find the area of the plates, which I then used to find the radius of the circle, which I multiplied by 2 to get the diameter.

2. Mar 4, 2015

### rude man

Just what I would have done! Congrats!

3. Mar 4, 2015

### PhysicsMan999

CAPA says my answers are wrong though! The answers I'm getting are 0.00679 for the distance between plates, and around 0.07 for the diameter..

4. Mar 4, 2015

### Staff: Mentor

Did the system specify particular units to use? Is it finicky about significant figures?

5. Mar 4, 2015

### PhysicsMan999

Well, apparently I was entering them in the wrong order..even though it says nothing about the order to enter them in. Thanks!

6. Mar 4, 2015