Magnetic Forces & Fields 5/7/2014

Today we started learning about Magnetic Forces.  First we placed a magnet on our white board and placed the compass at various locations trying to trace a behavior of the magnetic fields.  When the magnet was place in the middle of a circle, the  the North side of the compass pointed away from the the north-side magnet and points all the way around to the South side of the magnet as we move.

All directions of the red arrows were pointing consistently as it was moved around the magnet

After an idea of what a magnetic field looks like, we brought out a highly sophisticated “over-head projector” and sprayed tiny magnet peppers to demo in real world the magnetic fields created by our magnet:

We can observe that at the poles the magnetic field lines point out and curve around in a circular pattern, a more accurate depiction 

Our model of the Iron fillings experiment (left). The side surface and one that entirely surrounding both poles have a net flux of 0 because the number of field lines enter the circle equals the ones exiting. 

Next we experimented how magnetic field affect moving charged particles in the oscilloscope

Making an magnetic field pointing into the screen (above) pointing outward of screen (below)

Prof Mason manipulating the electrons inside the poorly-shielded oscilloscope tube.

We then observe what happens to a non-magnetic copper wire near a magnet when we pass a current through the wire:

The current going through the wire is our velocity vector going horizontally and the magnetic field runs between the north and south poles is our magnetic field vector going vertically.  Using the right-hand rule, we confirmed the direction the wire move due to Force.

Next, we experimented with a copper rod and applied some current through it to see which direction it rolls

Just as what the right-hand rule suggested, it rolled outwards

Current passing through the copper rod.  We conclude Force is proportional to current as we turn it up

Next we did a bunch of calculations performed to find the strength of the magnetic field performed

All of the measurements including the final equation we derived to calculate the strength of the magnetic field is shown above, and the answer we came up with was roughly .0.011T, which seems a little low but not too unreasonable.

We wrapped up the day with several more calculations of non-uniform magnetic field which torque is involved: