May 7 2015 first day of magnetic

We put a small compass around a magnet to figure the direction of the magnetic field at that point. By defination, the direction of a magnet is from north pole point to south pole. 

we drawn 3 closed surface around the magnet, and then we calculate the net magnetic flux through the closed surface. We reach a conclusion that the net magnetic flux through a closed surface around a magnet is always 0.

Putting a large magnet around the wire electron gun. We can observe a clear change on the screen. It tells us that magnetic flux can influence electron, and magnetic and electric are not independent.

We draw those diagram to show how the charge will influenced by the magnetic field. In general, the force apply on the charge due to its motion in the magnetic field is the cross product of qv and magnetic field.

This experiment shows that there is also force apply to a wire has current from magnetic field, and the direction is depended on the magnetic field direction and current direction.

We perform a simple question apply formula F = qvbsin(a) to solve for the charge of a moving particle in a magnetic field.

This graph shows the moving particle in magnetic field in 3D. The motion of the particle is more like a circular motion. Also, we can apply formula from circulation motion. Magnetic force is always perpendicular to its velocity, thus, it plays a role of centripetal force.  

We solve a simple question for the magnetic given its velocity. As well as F = qvBsin(a), we used Fc = mv^2/R to solve the question.

Similiar to moving particle, the force on the wire has current pass throught is also a product of length vector, current and magnetic field. Above is the formula we derived.

Since there is force from magnetic field apply on the wire, if we make it a loop, it gonna spin, and during its spining, the torque changes.

We draw a diagram to show the netic force and net torque on a loop. Based on this, we believe that the loop will spin up and stop.

Now we are dealing with non-linear wires, thus, we applied calculus. The force is integral of IdL cross B(magnetic field)

Summarize: The first thing for today is we now that magnetic and electric have relationship, and this relationship is shown by the force that wire and moving particle are applied in magnetic field. The magnetic force is a cross product, thus, right hand rule is applied.