# What does the magnetic flux depend on?

## Homework Statement

Does the magnetic flux depend on the shape of the surface or on the enclosed current? Or both or neither?

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## The Attempt at a Solution

I have no clue. I guess a change in the enclosed current is a change in the field and thus a change in the flux, but I have my doubts about this reasoning. Thanks very much for your help!

## Answers and Replies

Simon Bridge
Homework Helper
You should be able to find an equation for magnetic flux in your notes.
The specifics will depend on context.

No more info was given in the question. Is it possible that the answer doesn't depend on the context?

You should be able to find an equation for magnetic flux in your notes.
The specifics will depend on context.
No more info was given in the question. Is it possible that the answer doesn't depend on the context?

Simon Bridge
Homework Helper
No - context is everything. The context comes from outside the question statement.
You will have done some sort of classwork recently ... what was that about?

No - context is everything. The context comes from outside the question statement.
You will have done some sort of classwork recently ... what was that about?
We have only learned the equation of magnetic flux, the integral of B⋅da, and we have been busy with electromotive force. Perhaps that has something to do with it? The question is meant as general question about the definitions. It is stated as:

Is the following statement true or not true:

Magnetic flux depends on the shape of the surface and on the enclosed current.

Explain why.

Simon Bridge
Homework Helper
Now we are getting someplace:
Is the following statement true or not true:
Magnetic flux depends on the shape of the surface and on the enclosed current.
Explain why.
... this is actually a different question from the one you asked.
So what surface are they referring to, and what "enclosed current"?
You will probably have a diagram someplace showing a wire with a current in it and a surface drawn in somewhere too.
You can relate it to the equation for magnetic flux you have - or you may have a solution already to go with the diagram.

Now we are getting someplace:
... this is actually a different question from the one you asked.
So what surface are they referring to, and what "enclosed current"?
You will probably have a diagram someplace showing a wire with a current in it and a surface drawn in somewhere too.
You can relate it to the equation for magnetic flux you have - or you may have a solution already to go with the diagram.
No there is no diagram or current or surface or anything. It just a question about magnetic flux in general. :(

Simon Bridge
Homework Helper
No: it is a question specifically including an enclosed current and an area.
Is there no text book? Are their no class notes?
If there is no "area" in your notes, then what is that "dA" in your equation about?

It may be that you are supposed to investigate the equation in light of the question.

The full equation is:
$$\Phi = \int \vec B\cdot\text{d}\vec A$$
...it's a vector relationship which basically says that the flux is the sum of the magnetic field components perpendicular to the area multiplied by the area.

i.e. for uniform B passing through a plane surface of area A at and angle ##\theta## to the surface, the integral works out to: ##\Phi = BA\sin\theta##
Your question says the shape of the area matters. In the above example the shape of the area does not matter ... but is that generally true? What if the area was the surface of a cube instead?
Your question also asks about a current. There is no current in this example ... so you need another example to examine this part of the question.

Do you see how to handle this sort of thing?
You need to choose examples as thought experiments to see what matters to the definition - being careful to control variables.