On the Sources of Magnetic Fields

The topic this meeting is far far ahead of the topics that we have in Lecture class, so everything was quite new to me (but thinking about it, I don't think I'd learn anything in Lecture class if we discussed this :|). So basically, this meeting was all about the sources of magnetic fields, of which there are a number of.

The first source is permanent magnets, or the objects that naturally have a magnetic field associated with them. Basically that's it for permanent magnets.

The second source is the motion of charged particles, which is given by the equation:

where B=magnetic field vector, v=velocity vector, mu-knot=permeability of free space, q=charge of the moving particle, r=unit vector from position of particle to point where B is measured

This complicated equation basically says that the magnetic field is the cross product of the velocity and position vector wrt to where it is being measured times a constant given by the other terms. This means that there is no magnetic field when the velocity and position vectors lie on the same line (cross product is 0) while it is a maximum when the two vectors are perpendicular.

An extension of this source of magnetic fields is a current carrying wire. I won't put the equation anymore because I can't find a picture of it in Google, but I would say that the equation is quite similar in form to the one stated above.

Another source is a very long solenoid. When I first heard of this word, I was quite clueless of what it is. I previously heard of it in Physics 111 when we were discussing the divergence of a vector field. It was said that a solenoidal vector field is one that has 0 divergence at all points. I had no idea of what it meant, and still no idea at present. :| What I do know is how a solenoid looks like. It's basically a wire curled up to resemble a compressed slinky. This source of magnetic field also has an equation associated with it. Here:

Okay, I now want to talk about the experiment that we performed. Just like the other experiments that we had, this experiment is also a series of 'mini' experiments about the sources of magnetic fields.

The first mini experiment that we performed was measuring the magnetic field at different points around a permanent magnet (horseshoe and bar) using a magnetic field sensor and labquest. Honestly speaking, this part was quite arduous because the measurements were quite erratic and we had to take a LOT of measurements.

Then, the next thing that we did was to measure the magnetic field from the center of a horseshoe to the outside part of the horseshoe. Okay, that was quite confusing. Basically, we measured the magnetic field as a function of distance from the horseshoe.

We, then, proceeded to perform the next mini experiment. Here, we made use of iron fillings placed on top of a folder. Under the folder, a horseshoe magnet was used, and the iron fillings aligned themselves according to the magnetic field produced by the magnet. It was quite cool because it was like magic.

We were supposed to do Oersted's experiment. Well, actually, we did but it failed. So we had to scrap it off from the procedures list.

Then, we did the final mini experiment, which was to measure magnetic field outside a solenoid which carried a current. We, then, implemented different core materials and looked at how it affected the magnetic field.

... So that's all that we did this meeting.

The experiment was very long and tiring. We were there by 1 and ended at 4, making use of the full 3 hours this meeting. Initially, I thought that the experiment would be fast. But, boy, I was wrong. I haven't fully grasped the concepts of magnetic fields, so I don't know if our data makes any sense. Well, hopefully they do.:))

It's amazing how people (physicists) discovered how magnetic fields work, and even derived equations that explain how they occur. I'd never had known any of these if I didn't enter Physics.

I was also amazed by the device Labquest. I want one for my own.:D