If Magnetic flux is the strength of magnetic field that passes an unit area, (thereby flux PER unit area),then why is it given in units of $T m^2$ and not $T m^{-2}$?

  • $\begingroup$ Because T (Tesla) is not the unit of magnetic field $\mathbf{H}$ but the unit of magnetic flux density $\mathbf{B}$. $\endgroup$
    – Aaratrick
    Sep 12 '20 at 13:53
  • $\begingroup$ Tesla is unit of density so to get a fluid integral on an area you need to multiply density(T) with area(m2) $\endgroup$ Sep 12 '20 at 14:44
  • $\begingroup$ @Aaratrick if I go by what you said, then the definition of flux does make perfect sense. but then, what is the unit of magnetic field? also, what is this H thing? I was taught that B represents magnetic field, but you say that instead, B represents the density of the field.. Was I taught wrong? Plz clarify. $\endgroup$ Sep 12 '20 at 14:50
  • $\begingroup$ You are confused between B and H. In your other question you say magnetic field has units of A/m, which is true for H-field. The two fields are not the same, though both are often referred to as the magnetic field, and they have different SI units. $\endgroup$
    – ProfRob
    Sep 12 '20 at 16:20
  • $\begingroup$ @isaac_samuel You can take a look here, en.wikipedia.org/wiki/Magnetic_field . As Rob Jeffries has answered, flux is defined as the product of the flux density $\mathbf{B}$ times the area. However, the magnetic field, in SI at least, is $\mathbf{H}$ and the relation between them is, $\mathbf{B}=\mu_0 \mathbf{H}$ in vacuum. As for whether you were taught correctly, I believe the distinction between the two is not done in high-school physics. Look at the Wikipedia page, I think you will understand anything you were not taught $\endgroup$
    – Aaratrick
    Sep 14 '20 at 14:30

Flux is defined as field strength TIMES area.

  • $\begingroup$ why multiply them though? If I want to find the force exerted in a given area, I divide the magnitude of force by area, i.e., Pressure. Isn't this much same like that? To find the strength of the field (i.e., no of field lines ) passing through a unit area, shouldn't I divide the flux by area, instead of multiplying it, as you said? $\endgroup$ Sep 12 '20 at 14:45
  • $\begingroup$ Flux is not the strength of the field. It is the "flow" of the field.To find the strength of the field you do divide the flux by the area. To find flux you multiply field by area. $\endgroup$
    – R.W. Bird
    Sep 12 '20 at 20:32

The "magnetic flux density" (often called the magnetic field and given the symbol ${\bf B}$) has SI units of Teslas, T. It is a flux density, because a Tesla is also a Weber/m$^2$, where a Weber, Wb, is a unit of magnetic flux.

To get a magnetic flux from a magnetic flux density, you have to integrate over an area, i.e. $$ \Phi = \int {\bf B}\cdot d{\bf A}\ .$$

Clearly then, the units of flux $\Phi$ are either Tm$^2$, or Wb.


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