Permitivity and Permeability: What's the Difference and When Do We Use Them?

[dervast]

Hi i am trying to frigure out the similarities and differences between permitivity and permeability? When do we use the one or another term?

 

[berkeman]

Permitivity pertains to electric fields, and permeability pertains to magnetic fields. What textbook are you using for this anyway?

 

[dervast]

So its the same thing but the first term is for electricity and the second one for magneticity

 

[dervast]

permitivity is eo and permetabilty is m0 right?

 

[marlon]

Hi i am trying to frigure out the similarities and differences between permitivity and permeability? When do we use the one or another term?

It's permiTTivity :)

Although this is a very good question, you really should have asked about the RELATIVE permeability and permittivity.

Why ? Well, because the the "permeability and permittivity" are just the units or the "permeability and permittivity" of the vacuum. If one talks about relativity permittivity of 3.9, than one really means 3.9 times the permittivity of the vacuum.

Now, what are these guys ? Well, they are indeed quite similar since permittivity refers to "electrical phenomena" and permeability refers to "magnetic phenomena".

Let's take the (relative) permittivity. Basically, this quantity refers to how much electrical charge an object can store once you apply a voltage onto it. In other words, it expresses how an object "reacts" through rearrangement of the electronic distribution of the material, if you apply an E-field onto it. As an example, just think of what happens if you apply a voltage onto a medium with 5 plus and 5 minus charges. The charges will separate. There is another, more famous quantity that expresses this : ie the dielectric constant. This actually is the relative permittivity of a dielectric (ie a polarizable medium).

The exact same thing exists for magnetic media. Keep in mind that the electrons are NOT represented by magnetic monopoles ! This is the only assymetry between electrical and magnetic phenomena.

regards
marlon

 

[cbravo135]

One thing that separates the two is that permittivity is a scalar and permeability is a tensor.

 

[Andy Resnick]

That's not true- both the permittivity and permeability may be tensor-valued.

 

[Bob S]

The speed of light, 2.9979 x 10⁸ meters / sec, is equal to the inverse square root of the product of e₀ and u₀. The impedance of free space, 377 ohms, is equal to the square root of the ratio of u₀ / e₀. Virtually every material has a dielectric constant and index of refraction > 1, both associated with e₀, while very few materials have a relative permeability u > 1 (magnetic materials), associated with u₀. e₀ is associated with charge, while u₀ is associated with currents.

 

[MarkoASI]

Can someone help me to know the same difference but referred to hydraulic flow rate? thanks!

 

[Glen Bartusch]

The speed of light, 2.9979 x 10⁸ meters / sec, is equal to the inverse square root of the product of e₀ and u₀. The impedance of free space, 377 ohms, is equal to the square root of the ratio of u₀ / e₀. Virtually every material has a dielectric constant and index of refraction > 1, both associated with e₀, while very few materials have a relative permeability u > 1 (magnetic materials), associated with u₀. e₀ is associated with charge, while u₀ is associated with currents.

Where did you get the idea that the impedance of "free space" is 377 Ohms? Since impedance is defined as "the total resistance in [any] circuit," that would mean that the impedance of free space would exceed several million Ohms, provided my DVM probes aren't so close together that they electrically short.

 

[Claude Bile]

Think of permittivity and permeability as "bang for your buck" constants. That is, how much E or B field you get for a given amount of charge at some velocity, v. Permittivity applies to E fields, permeability applies to B fields.

P.S. Glen, Bob S. is correct, the impedance of free space is ~377 ohms.

Claude.

 

[f95toli]

Where did you get the idea that the impedance of "free space" is 377 Ohms?

From e.g. any book which includes a chapter on basic antenna theory.
And the 377 Ohms of space can "short" a circuit when you are working at high frequencies, so it is a "proper" impedance;

 

[Saad Ahmed]

How we calculate permitivity and permeability of free space?