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Permittivity of free space in physics

  • Thread starter jimmy42
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  • #1
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Hi,

In my physics book I have two values for the permittivity of free space:

8.854x10^-12 c^2 N^-1 m^-2

and

8.988x10^9 N m^2 C^-2

What is the difference between these two? When would I use one or the other?

Thanks.
 

Answers and Replies

  • #2
gneill
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Hi,

In my physics book I have two values for the permittivity of free space:

8.854x10^-12 c^2 N^-1 m^-2

and

8.988x10^9 N m^2 C^-2

What is the difference between these two? When would I use one or the other?

Thanks.
One is the permittivity of free space, εo, typically seen in Gauss' Law, while the other is 1/(4πεo), typically seen as the proportionality constant used in Coulomb's law.
 
  • #3
Doc Al
Mentor
44,912
1,170
In my physics book I have two values for the permittivity of free space:

8.854x10^-12 c^2 N^-1 m^-2
That's the permittivity of free space, usually symbolized as ε0.

and

8.988x10^9 N m^2 C^-2
That's Coulomb's constant, usually symbolized as k. (Not the permittivity of free space!)

What is the difference between these two? When would I use one or the other?
They are related by: k = 1/4πε0.

So you can write Coulomb's law as:
F = kq1q2/r2 = 1/4πε0 (q1q2/r2)
 

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