- #1

tjvogel

- 2

- 0

## Homework Statement

A bar magnet with

**magnetic dipole moment 0.5 A m**lies on the negative x-axis, as shown in the diagram. A compass is located at the origin. Magnetic North is in the negative z direction. Between the bar magnet and the compass is a coil of wire of

^{2}**radius 1.5 cm**, connected to batteries not shown in the picture. The distance from the center of the coil to the center of the compass is

**9.9 cm**. The distance from the center of the bar magnet to the center of the compass is

**22.5 cm**. A steady current of

**0.836 amperes**runs through the coil. Conventional current runs clockwise in the coil when viewed from the location of the compass.

http://tinyurl.com/27o8lfk

## Homework Equations

Bmagnet= [tex]\mu[/tex]

_{o}/4*[tex]\pi[/tex]*(2*[tex]\mu[/tex])/r

^{3}

Bcoil= [tex]\mu[/tex]

_{o}/4*[tex]\pi[/tex] * (2*pi*R

^{2}I)/(z

^{2}+ R

^{2})

^{3/2}})where mu_o/4 = 1e-7

mu= magnetic dipole moment =.5 A*m

^{2}

R= radius= .015

## The Attempt at a Solution

I understand that Bmagnet= negative Bcoil to keep needle pointing north.

I have tried a couple things, but here is what I think it is, and want to make sure that I get it right.

Bmagnet

= 1e-7* [(2*.5)/.225)]

=4.444e-7

Bcoil

=1e-7*(2*pi*.015

^{2}I)/(.015

^{2}+ .099

^{2})

^{3/2}

=1.17727e-7And my assumption that I would then proceed to divide Bmagnet by Bcoil to get the number of loops...

=4.444e-7/1.17727e-7

=3.7752 Turns

Is this right? or am I doing something wrong?

thanks!

(and sorry for the sloppiness/inconsistency of the formulas... I got tired of trying to fix it. still getting used to the formula inputs... esp greek letters)