Elementary question on Electric flux units

• jonjacson
In summary: This is not SI.In summary, the net flux over a closed surface can be calculated by taking the surface integral of the electric field divided by the permittivity of space, according to Gauss' law. In CGS (Gaussian) units, the net flux is simply equal to the charge, while in SI units, the net flux has units of Newton meters squared per coulomb. The book "Purcell's Classic" primarily uses CGS units, although it briefly mentions SI units, which can potentially cause confusion.
jonjacson
The net flux over a closed surface is:

Flux = The surface integral of the field E = charge / permitivity in space (Gauss law)

The permitivity in space is:

8.85 10-12 Coulombs2/N m 2

So I understand the units of Flux are:

Newton meter2/Coulombs

Is this correct? I don't understand why in a book they say that the net flux is simply the charge, ignoring the permittivity units.

ALternatively the permittivity could be given in Farad/meter so our flux would be:

Is this correct?

Thanks!

Nobody?

jonjacson said:
in a book
a book, eh ? Are they talking about ##\vec E## or about ##\vec D## ?

Does your book use SI units or Gaussian? You should really identify the book.
In SI, electric flux is volts meters. (Because electric field is volts/meter, and flux is an integral over area)

jonjacson said:
I don't understand why in a book they say that the net flux is simply the charge, ignoring the permittivity units.
As a wild guess, perhaps it uses Gaussian units, in which the vacuum permittivity constant ##\varepsilon_0## does not exist.

https://en.wikipedia.org/wiki/Gaussian_units

[ah, now I see Khashishi beat me to it!]

Ok, so if it is gaussian units it is just the charge, if it is SI units we have what I said at the start.
I hope this is right, if not let me know.

Did you miss
Khashishi said:
Does your book use SI units or Gaussian? You should really identify the book.

BvU said:
Did you miss

It is Purcell's classic. It is a fantastic book, it says in gaussian units it is just the charge, but in SI doesn't explicitly say "these are the units", I wanted to check, since I consider that very basic.

Purcell Ch1 (probably the rest too) is CGS. He touches upon SI which to me is potentially confusing. Check out appendix E where he says 'in our CGS system'.

What is Electric Flux?

Electric flux is a measure of the electric field passing through a given area. It is calculated by multiplying the electric field strength by the area perpendicular to the field. The unit of electric flux is N*m^2/C.

What is the SI unit of electric flux?

The SI unit of electric flux is N*m^2/C, which is equivalent to volts (V).

What are the different units of electric flux?

Apart from the SI unit of N*m^2/C, electric flux can also be measured in other units such as volts (V), volts per meter (V/m), newton meters squared per coulomb (N*m^2/C), and weber (Wb).

How is electric flux related to electric field?

Electric flux and electric field are directly proportional. This means that as the electric field strength increases, the electric flux passing through a given area also increases. Similarly, if the electric field strength decreases, the electric flux also decreases.

Why is electric flux important in electromagnetism?

Electric flux is important in electromagnetism because it helps us understand the distribution of electric fields and their effects on charges. It is also used in many practical applications such as capacitors, electric motors, and generators.

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