PHY C23: Magnetic Flux

New chapter! Let’s start off with a very important concept:

  • Magnetic Flux
    • Φ = BA sin θ

Remember my post on Magnetic Flux Density?

Now we turn to a similar term:

Magnetic Flux

What is magnetic flux?

The product of magnetic flux density & cross-sectional area normal to the lines of flux.

It is represented by Φ

For a uniform field B making an angle θ with a cross-sectional area A,

Φ = BA sin θ

Its unit is the weber (Wb)

1 Weber is equal to 1 Tesla multiplied by 1 meter-squared

Wb = Tm2


Confusing? Let’s look at that 3D image illustrating B again:

Here, the cross-sectional are A is perpendicular to the magnetic field lines.
Φ = BA

Let’s look at the general case now:

Here, the cross-sectional are A is at an angle θ to the magnetic field lines.
Φ = BA sin θ

Now let’s compare different cross-sections for different areas & different magnets:

Magnetic flux density (B) is represented by the number of lines passing through an area PER UNIT AREA.Magnetic flux (Φ) is represented by the number of lines passing through an area.
These areas have the SAME magnetic flux density, B.

They have the same density of lines, so the STRENGTH of the magnetic field is the same.
These areas have DIFFERENT magnetic flux, Φ.

They have a different total number of lines.
These areas have DIFFERENT magnetic flux density, B.

They have different densities of lines, so the STRENGTH of the magnetic field is different.
These areas have the SAME magnetic flux, Φ.

They have the same total number of lines.

We’ve seen why flux density is so important – it is useful in calculating the forces exerted by a magnetic field.

So…


Why is magnetic flux so important?
It is useful in explaining Electromagnetic Induction.

We’ll cover that in my next post – see you there!

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