# Magnetic field produced by a current

1. Jun 29, 2011

### Tosh5457

I'm translating the problem from portuguese to english, so I'm sorry if there are errors.

1. The problem statement, all variables and given/known data
Determine the magnetic field on the center of the circumference produced by the current in the conducting wire (the circumference is made of conducting wire too). The current goes from left to right, and on the circumference it's clockwise.

2. Relevant equations

Biot-Savart Law: $B = \frac{\mu_0}{4 \pi} \ \int \frac{ I \ \vec{dl}\times \hat{r}}{r^2}$

3. The attempt at a solution

I can't relate dl with r (the distance from dl to the center) nor the angle, which I must do to compute the integral.

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2. Jun 29, 2011

### Staff: Mentor

The trick to this question is to see that the B field in the center of that loop is the sum of the B-field from the loop itself, plus the B-field from the long straight wire....

3. Jun 29, 2011

### Liquidxlax

yep the right hand rule can also gives a good indication as well

on the straight wire the current goes right so curling your fingers indicates the field points down. On The loop the current goes clockwise tot he magnetic field is again down.

For the long straight wire you must relate the center of the ring to a segment dl on the long straight wire that is a distance r1 away. which you can relate to theta by integrated from pi/2 to -pi/2

4. Jun 29, 2011

### Tosh5457

So, dl = rdθ? And how do relate I r with θ?

5. Jun 29, 2011

### Staff: Mentor

Your book should have a solution for the B-field from a long straight wire. And a separate solution for the B-field at the center of a single loop of wire. Do you see how they set up the integrals for each of those...?