# Magnetism question

1. Mar 6, 2006

### jimmy_neutron

I have some questions regarding magnetic field lines, i have provided the questions and my proposed answers. help is appreciated.

Q1. Draw the magnetic field lines around a current carrying wire of length L.

A1. Since the current is moving in the direction given, using the RHR, does this mean the magnetic field is in the clockwise direction, and if so would the answer be??:

Q2. Take the wire in the previous question, join its ends and form a circular current loop of radius R, where R= L/2pi. Draw how the magnetic field lines in Q1 would be changed.

A2. I am not sure what it would do to the field lines, possibly reverse them into counterclockwise?

Last edited: Mar 6, 2006
2. Mar 6, 2006

### xman

which direction is the current flowing in?

3. Mar 6, 2006

### jimmy_neutron

current is flowing to the right

4. Mar 7, 2006

### xman

if current is flowing to the right then in the plane of the loop if we point our thumb in that direction and wrap our hands around the wire the current on the inside of the loop will be coming out of the plane , and will be going into the plane for points outside the radius; that is, for points where s<R the B field is out of the plane and for s >R into the plane of the loop, where s is our radial distance from center of loop and R is the radius of the ring. for points outside the plane what does the field look like..can you visualize it? ...hope this helps, x

Last edited: Mar 7, 2006
5. Mar 7, 2006

### jimmy_neutron

When you asked for the direction of the current, I assumed you were asking for the current in the straight wire. However, for the direction of the curent in the loop, is not given in the problem and must be determined. The loop is the product of the straight wire being bent and joined together at each end. Would the current still be moving right, as it was in the straight wire.
If so would the magnetic field look like this?
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html

6. Mar 7, 2006

### xman

yeah, that's the idea. note that maxwell's eq
$$\vec{\nabla} \cdot \vec{B} =0$$
is still satisfied. also that in the plane of the loop the magnetic field for points outside points down with respect to the loop, and points up for points inside the loop.

Last edited: Mar 7, 2006