Magnetic field produced at point P

[Rijad Hadzic]

Homework Statement

https://imgur.com/gallery/vCOZq

Its question 26, and the figure can be seen at figure 30.26

Derive and expression for the magnetic field produced at point P due to the current carrying wire shown in figure 30.26. The curved parts of the wire are pieces of concentric circles. Point P is at the center.

Homework Equations

b = \mu IR^2 / (2)(R^2 +y^2)^{3/2}

The Attempt at a Solution

Ok so in the above eq setting y = 0, I get

b = - (\Theta /2pi) * ( \mu I /2R_1 )
(\Theta /2pi) because we are only looking at a portion (\Theta /2pi) of a circle.
for the wire closest to the point P.

I say the magnetic field is going INSIDE the page at point p, which means -z axis, but my book is telling me the field is out of the page.

Is my book wrong here? I don't see how, using the simple right hand rule, the field could possibly be pointing out of the page.

 

[kuruman]

I don't see how, using the simple right hand rule, the field could possibly be pointing out of the page.

I don't see it either. The outer arc generates a field that is out of the page that is weaker because its radius is larger. The straight segments, of course, generate no field at point P.

 

[Rijad Hadzic]

I don't see it either. The outer arc generates a field that is out of the page that is weaker because its radius is larger. The straight segments, of course, generate no field at point P.

Yup. And this answer is coming from the instructors manual for this book. Such a shame. Maybe someone will find the trick? (if there is one?)

 

[kuruman]

Yup. And this answer is coming from the instructors manual for this book. Such a shame. Maybe someone will find the trick? (if there is one?)

You may wish to take your solution to your instructor and ask what's going on.

 

[Rijad Hadzic]

You may wish to take your solution to your instructor and ask what's going on.

Yup that's what I'm going to have to do...