B Weber and flux density

1. Mar 28, 2017

Glenn G

Hi,
Eqn B = phi/A

For flux density so 1T = 1Wb/m^2

Often wondered about a Weber and found on a site that 1 Wb is 1 x 10^8 lines of magnetic flux! Does this sound right that an exact amount of flux lines represents 1weber? I always thought that the concept of webers was a relative idea and not representing a physical amount of field lines?

2. Mar 28, 2017

Khashishi

Field lines are just a cartoon for picturing the magnetic field. They aren't real things.

3. Mar 29, 2017

Glenn G

Does this mean that a magnetic field acts at all points in space around a magnet? How then to interpret magnet flux density if it's not amount of flux per m^2. Also difficult then to think about em induction occurring when cutting across line but not when moving parallel to field lines? How can we think of this if there are no 'lines' as such?

4. Mar 29, 2017

Khashishi

Yes. There are no "gaps" between field lines. You can think of the lines as infinitely dense, passing through every point in space, but only a small fraction are shown in any diagram for clarity. The lines are just a way to visualize a vector field.
It's the perpendicular part of the magnetic field going through a differential element of surface.
There is a vector at each point in space. Cutting across a line means the same thing as moving in a direction not parallel to a vector.

There's nothing wrong with the concept of field lines. It's just that the number of field lines in a picture is arbitrary, and the magnetic field itself is smooth and not bunched into discrete threads.

5. Mar 29, 2017

cnh1995

As khashishi said, the lines are just a cartoon. In electrostatics, you may find stuff like 4π lines of flux. How can the number of lines be 12.56?

You can think in terms magnetic field B (also called as 'magnetic flux density'). If I am not wrong, the basic definition of magnetic field B comes from the Lorentz force equation F=qvB. The surface integral of B is the magnetic flux linking with that surface.

If you want to think in terms of flux lines, crowded lines means more flux density
(which means higher magnetic field).
The lines are just a pictorial representation of the field.

6. Mar 29, 2017

Glenn G

Thanks that really helps. I like the idea of treating it as a vector at a point.