Day 23 Faradays Law and Lenzs Law

At the beginning of the class, we did a review problem of finding the force and the magnetic field.

This picture shows the activity that when the two lines were charged they got closer.

We thought that there were actually forces between two wires that caused them close to each other, but because the power is alternating current, there is no force.

The graph on the left is our prediction of Magnetic Field vs. time, and the right graph is the magnetic field vs. time graph made by professor. They actually look alike.

We also used logger pro to make a graph 

On the top example, the flux is 0 because the magnetic field go through. But in the bottom example, the magnetic field actually is perpendicular to the side. So the flux is B*a*b.

This is an experiment about the magnetic field in a loop.

We collect data.

The professor demonstrated a experiment which he put a magnet through the loop and the meter would go up and down as the magnet go in or out the loop.

These are 4 ways that the strength of current is influenced.

This is another experiment when we have current from a coil and magnet.

When we put a ring of aluminum and applied current to it, the ring floated.

However, if there is a gap between the ring, it will have no effect.

Here is another activity, when dropping the magnet into the magnetic tube, it will drop slower than the non-magnetic tube.

This is a diagram of how the magnetic field and velocity of how the previous activity works.

The left graph is the graph of the flux and electromotive force. They are the same but shift a little bit. And the right picture we derived the equation of flux and electromotive force.

Conclusion

In today's class, we first reviewed a problem about force related to magnetic field, then we talked about Faraday's Law, flux through a loop, current from a coil and magnet, Lenz's law, and finally we derived the equation and drew the graph of flux in a coil as function of time and electromotive force.

Day 22 Motors & Magnetic Fields

At the beginning of the class, we drew the microscopic level different between ordinary pin and the magnetic pin. The magnetic pin is in order, and ordinary pin is not in order.

We listed two ways to destroy a magnet, which are heating and hitting because they can cause vibration that reorganize the domains.

The professor demonstrated the activity by heating the pin. The result was it lost its magnetic.

This picture shows another exercise where we give the loop a magnet field, the direction is upward. We found that only the top and the bottom have force and they cancel with each other. We also found F = BIL and τ = 1/2 BIL^2 

We did a problem by using the question highlight in yellow.

Professor showed us an electric motor 

There are three ways that a motor would break, the brushes, the commutator, and the coil contact foils.

Then we started doing an experiment called electric motor. We need to set up the apparatus like in the diagram.

There are four situations of the motion of electric motor. We found that when the direction of the current change or direction of magnetic field change, the direction of rotation will also change.

These are the answers from lab manual.

Then we performed another experiment about making a simple electric motor by coated wire, two paper clip, a bar of magnet

This video shows how the experiment is successfully done~

In the picture shows the hall effect and hall voltage Vh = B*I/p*q*t

The next activity is giving the bar in the magnetic field and observing how the compass arrow will turn

We predict that the compass would point like a circle.

In this picture, the result and our prediction match.

This picture shows the change in opposite current also make the compass circle circle point the opposite direction. 

In this activity, the professor let us draw where the compass will point in such wiring arrangement. And our prediction is on the right.

We found B as u_o*q*dv*r/4π*r^2

We also found the relationship between Force of Magnetic field and force of the electric field.

Conclusion

In today's class, we first discussed about the magnet, then we talked about the force and torque related to magnetic field. Then we also talked about magnetic dipole moment. We also looked at the electric motor and built a simple electric motor. Then we also learned the hall effect and Biot-Savart Law. Finally we figured out the relationship between  force of magnetic field and force of the electric field

Day 21 Magnetic Forces and Fields

At the beginning the of class, we have a bar magnet and a small compass. We need to draw which way the compass points when moving the compass around the magnet. The arrows leave from north pole and direct to south pole.

This shows all arrows together.

The professor put iron sprinkled around the magnet and we observe that the picture is like what we drew.

In this picture, we draw three loops, which are the loops contain one pole, both poles, and no pole. The number is how many arrow in and out the circles.

This is the large magnet that the professor rub a wire on to make the wire a magnet. 

We used the equation to find magnetic flux

We found that magnetic net flux is always 0

The professor shows us that when we put magnet next to the oscilloscope, the point on the oscilloscope will go different direction as the magnet moves.

In this activity of magnetic forces on moving charges, we found out two vectors of points.

We used the equation F = q*v*B to find the unit of B.

In this activity of using Lorentz Force in calculation, we found the magnitude and direction of the force exerted on the proton by the magnetic field.

By the equation F=q*v*B, we calculation the Force, and acceleration.

Also, by applying centripetal force, we can calculate the radius.

We also did a problem and used the equation r= mv/qB and v = 2πrf to find B.

In this activity, the professor put a wire between the magnet and connect to the battery. We observed that the wire will move up and down depends on the charges.

In this activity, we answer 4 questions on the lab manual.

                                    a. v = L/t

                                    b. I = q/t 

                                    c. F = qvB = ILB

                                    d. dF = IdLB

Then, we did an experiment called magnetic force on a current loop.  

We need to found the direction of the magnetic field and the direction force.

Then the professor performed the experiment and showed us that the loop will spin up 90° 

Conclusion

For today's class, we learned about magnetic forces and magnetic field. We first looked at how the arrow of compass would turn near a magnetic and then did a lot of activities about magnetic forces, magnetic field, Lorentz Force on a current loop.