Lab Report Day 20 - Magnetic Field, Lorentz Force

Magnetic Field Lines Around a Magnet


Using a compass, we can draw the direction of a bar magnet as we rotated the compass around the magnet. North is attracted to South, and South is attracted to North. We can also draw the magnetic field line by putting a compass around it. 
Gauss's  Law in Magnet is defined as ∫B∙dA. ∫B∙dA=0 because there is no monopole, in every single magnet, there will always be south pole and north pole. Thus, the net flux is always zero. 



Afterwards, we spray some Fe power near a magnet to see the magnetic field. 
Magnetic fields go from positive to negative. 


Electric Field Lines


Lorentz Force

Using a magnet, professor Mason use a magnet to approach the green spot of electrons on the oscilloscope from two different directions. When it's from the sides, we can see that the electrons would move perpendicular to the magnet.When the magnet is directly towards it,  the spot does not move. This shows that  the velocity and the magnetic field needs to be perpendicular, giving us the equation F=qVxB or F=qvBsinθ. The right hand rule can also be used in order to help determine the direction of the force.

Lorentz Force Large Magnet Demo

For this lab, Professor Mason brought out a large magnet and set up a copper wire across and in between the magnet.

A large current goes across the wire and we see that the wire moves. It seemed to jump up.

Then we reverse the direction of current. We can see that the wire jumps down.
The velocity of the electrons is going through the wire, the direction of the magnetic field is going across the poles of the magnet, and the force is perpendicular to the velocity and magnetic field (Lorentz Force= F=qVxB or F=qvBsinθ). This copper wire is a current carrying wire, which is a line of electrons moving with some velocity.

 Finding Net Force

For this lab, we find the total force on a wire by using a spreadsheet. A semicircular wire is cut into 15 segments. θ, sinθ , and F are found for each segment and add them up. (F= IL x B) It can be observed that there is a maximum first at 90 degrees and a minimum on the sides. 

Summary:
In today's class,we learn how to find a force caused by Magnetic Field. We learn how to use the right hand rule to determine the direction of L, B or F. We learn how to solve problems.