# Permittivity of free spaces

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1. May 29, 2015

### wasi-uz-zaman

Hi please tell me physical significance of permittivity of free space, how can we explain its value having unit of F/m

2. May 30, 2015

### Svein

Creating a capacitor with "free space" as the dielectric (or any sort of dielectric), the capacitance is proportional with the permittivity, the area (m2) and inverse proportional with the distance between the plates (m). Therefore, to calculate the capacitance, you multiply with the area and divide by the distance - and you end up with the capacitance (in F).

3. May 30, 2015

### Staff: Mentor

In a parallel plate capacitor, lines of flux reach across the void to terminate on charges of opposite sign on the opposing plate.
Svein has ably demonstrated the units of $\epsilon$ based on the formula for capacitance, $C=\epsilon\frac{A}{d}$

The units of $\epsilon$ are not so obvious if you try deconstructing this speed of light formula, $c=\dfrac 1{\sqrt{\epsilon\mu}}$

4. May 30, 2015

### helter skelter

Changing the topic,in coulumbs law
1\4 pi epselon = 9x10^9 but on solving I'm not getting the same

5. May 30, 2015

### Staff: Mentor

If this is a new topic, you need to start a new thread.

If this is still on the units of permittivity, explain what it is you are trying to solve.

I doubt the formula could be 1\4 pi epsilon. It is almost surely 1/(4 pi epsilon).