# Flux Density (1 Viewer)

#### bjw22

##### Member
What is the difference between magnetic flux and magnetic flux density??

I describe magnetic flux as the number of field lines, and then magnetic flux density to be the number of lines passing through a given unit of area. Is this correct??

#### Exp

##### Member
yup, that's exactly right!

• bjw22

#### Drdusk

##### π
Nope that is wrong, magnetic flux = BA i.e. the number of field lines passing through a certain area. Magnetic flux density is the strength of the magnetic field, i.e. the spacing of the magnetic field lines.

#### bjw22

##### Member
Nope that is wrong, magnetic flux = BA i.e. the number of field lines passing through a certain area. Magnetic flux density is the strength of the magnetic field, i.e. the spacing of the magnetic field lines.
An independent trial paper has solutions that state "magnetic flux measures the amount of field permeating an area in Webers whereas magnetic field density, refers to the amount of field per square metre of area, measured in Webers per square metres or Teslas.

So I think original definition is a bit more exact but spacing of magnetic field lines is what changes the flux density - size of area changes spacing.
Say a little square and a big both had 5 field lines passing through, therefore the magnetic flux is equal in both but the magnetic flux density is greater in the little square.

#### HAX0R

##### Member
Nope that is wrong, magnetic flux = BA i.e. the number of field lines passing through a certain area. Magnetic flux density is the strength of the magnetic field, i.e. the spacing of the magnetic field lines.
That's more or less what the OP is saying.

• bjw22

#### Drdusk

##### π
An independent trial paper has solutions that state "magnetic flux measures the amount of field permeating an area in Webers whereas magnetic field density, refers to the amount of field per square metre of area, measured in Webers per square metres or Teslas.

So I think original definition is a bit more exact but spacing of magnetic field lines is what changes the flux density - size of area changes spacing.
Say a little square and a big both had 5 field lines passing through, therefore the magnetic flux is equal in both but the magnetic flux density is greater in the little square.
In your original one you said magnetic flux is the number of field lines without mentioning area. Magnetic Flux density is the amount of magnetic flux over a certain area i.e. BA/A = B, hence magnetic flux density is the strength of the B field, in simple terms to make it easier, its how close or far apart the lines of the magnetic field are. Magnetic Flux DENSITY is INDEPENDENT of area If a little square and a big square had 5 field lines passing through it the bigger square would have a larger magnetic flux because it has greater area(provided that both have a magnetic field of the same strength) Remember Magnetic Flux = BA.

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#### Drdusk

##### π
That's more or less what the OP is saying.
No its not, it makes a big difference. It can cost you a mark which it did for some people I know