# Electromagnet magnetic field strength

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1. Mar 26, 2016

### Sum Guy

1. The problem statement, all variables and given/known data

2. Relevant equations
$\oint_{C} Bd\ell = \mu I_{enc}, B_{normal}$ continuous across boundary, $H_{parallel}$ continuous across boundary

3. The attempt at a solution
$$\oint_{C} Bd\ell = \mu I_{enc} \rightarrow B = \frac{\mu NI}{2\pi r}$$

Any help much appreciated. How should I proceed?

2. Mar 26, 2016

### Staff: Mentor

How did you do the "->" step?
Where do you run into problems with the other parts?

3. Mar 26, 2016

### Sum Guy

I just don't know how to even get started really. I did the "->" just by applying amperes law, ignoring the ends of the core (because you could just take a line integral to avoid them).

4. Mar 26, 2016

### Staff: Mentor

... and ignoring the core, and assuming B is uniform in the gap. That is fine, but you should be aware of assumptions like that.

The untapered magnet works in the same way as the tapered magnet, you just have fewer variables (which makes it a bit easier).

5. Mar 26, 2016

### Sum Guy

So what should I do? :S

6. Mar 26, 2016

### Staff: Mentor

The same thing as for the tapered magnet.

7. Mar 26, 2016

### Sum Guy

Please could you give me a clue as to what integral I would have to do? I'm struggling to see how I am meant to take account of the tapering in an integral amperean loop...?

8. Mar 26, 2016

### Staff: Mentor

It is literally exactly the same as the exercise you solved already, just with different letters because the ends are not tapered.

9. Mar 26, 2016

### Sum Guy

I haven't solved the tapered case? I don't know how to..?