Electromagnet Induction

We did an active physics activity to start the class. In this activity we showed the relationship between flux and EMF.

In the above pictures Professor Mason showed what would happen to a rod when a current is run through it and it has a magnetic field going upward. In the first picture the the current is going away from me so the rod is pushed away from the magnet. In the second picture the current is coming toward me so the rod is pulled toward the magnet. We can figure out these directions by using our right hand rule.

Afterward we did another activity in active physics. In this one we examined the connection between current, EMF, and Magnetic Flux. We can see that flux depends on area so if area increases or decreases so does flux.

On the left side of the board we derived relationships between induced current and induced voltage. We also came up with relations between capacity and current and electric potential. On the right corner we derived the unit for inductors. In the center of the board we solved for inductance of a rod with a given radius, length, and number of turns of coil around it. 

This was another activity we did from active physics. In this activity we examined a RL circuit (circuit containing a resistor and an inductor). 

In the above picture we examine the graphs of current vs. time and voltage vs. time when there is an inductor.

  

Force due to Magnetic Fields and Currents

In the pictures above Professor Mason used a Halls Effect Sensor to determine the magnetic field in the classroom. He spun it around and from the graph we can see that it was strongest in the initial direction he was pointing it, then it slowly dropped until he bottomed out, which was the opposite direction he started at, and then it slowly rose to its max when it was going back to it's initial direction.

This was our experimental graph. We used the Hall Effect Sensor to determine the magnetic field due to copper wires around a test tube. Our readings were a tad low over the course of our experiment due to the Hall Effect Sensor being pointed slightly in the wrong direction. This wasn't noticed by us until our last reading, which was much lower than the previous reading. After correcting the direction we got a much larger reading for our final run.

In this picture was can see that when two currents (through wire) are next to each other and in the same direction, force vectors which oppose each other are created. The graph on the bottom shows that the magnetic field takes the shape of a sinusoidal graph.

In the above 3 pictures Professor Mason showed us that the magnetic field created by a current through loops was much higher when there were many more loops of wire. Also the speed at which the magnet was moved in or out effected the strength of the field.

In the device above a current is run through the copper wires on the bottom of the device, which creates a magnetic field in an upward direction. In the upper portion of the device an opposing field and current is created as a result. 

In the above two pictures Professor Mason showed that the current created by the bottom portion of the device was able to light the bulb connected to this wooden ring. At a greater distance the light was lowered showing that the current was much stronger when it was closer to the copper wires.

In the above two pictures we can see the opposing magnetic fields in action. The first picture shows copper and the lower picture shows the aluminum. The aluminum is more susceptible to the field and as you can see it was blown off the device with the same amount of current that barely lifted the copper.

Steel was also lifted.

We can see in the above picture that a slight gap in the ring would stop a magnetic field from being created.

We can see in the above picture that if we have a longer solenoid, larger magnet, increased radius of solenoid, or if we increase the velocity of the magnet that we can increase the magnetic field created.

In the above two pictures, Professor Mason showed what would happen if a magnetic object was dropped through an aluminum cylinder. The magnet falling through the aluminum cylinder creates a current in a counterclockwise direction which creates magnetic force in an upward direction which causes it to fall much slower.

In the above picture we show what an emf graph would look like compared to the magnetic field graph over time.

Magnetic Fields Due to Currents

Professor Mason showed that when a magnetized metal is heated it will lose it's magnetism. This is due to the fact that when an object is heated its molecules speed up, causing the dipoles to also move out of their magnetized orientation.

Here we showed that when you magnetize a metal you are simply causing all of its poles to point in one direction, which gives it an attraction. We also figured that to destroy a magnet you would either need to get it hot in order to cause the all of it's molecules to move at a high rate or hit it really hard with something like a hammer. We also determined how to solve for the electric dipole moment.

Here we were able to get these wire loops to spin by running a current from the batteries through the wires. The magnet below created a force vector which cause the wire to spin upwards. The momentum of the spin would keep the wires spinning when it was completely parallel to the magnet and then as soon as there was any angle between the area vector and the magnetic field the process would repeat.

We talked a bit about the tiny motors that run various little devices. The first things to likely break are the Commutator and the brushes. We also talked about how the current direction could affect the rotation of the motor.

In the above 3 pictures Professor Mason ran a current through a pole surround by compasses. The compasses would react based on the direction of the current. The magnetic field would go in a counterclockwise direction and when the current was reversed the field went in a clockwise direction.

In the top two pictures Professor Mason ran a current through the wires and he used a 3 dimensional compass to show which way the field would point at various locations on the setup.

This board picture showed which direction the magnetic fields would go in the board setup and the compass setup. We also derived equations to determine the magnetic field, and the comparison between a magnetic field and an electric field.

Magnetic Fields

Professor Mason showed us what happens when iron shavings are sprinkled over a magnet. You can see that there is a wave pattern around the north and south ends of the magnet. The shavings are repelled from the north end and brought into the north end.

We used the compass to determine where the magnetic field was going at different points on the magnet.

This is the picture we were able to conclude with. Magnetic fields would go out of the north end and into the south end.

This is a large magnet that Professor Mason used for various experiments in the class.

We put surfaces around the fields at certain locations. One on the south end, one in a random location, and one around the whole thing. We found that the Gaussian surface placed around the entire system and the on in the random location would have 0 net magnetism, while the one on the south end only had fields going in, so it was negative. We also see that when you break up a magnet you make smaller magnets, until the pieces are too small and you are left with just a useless piece of material.

Professor Mason demonstrates what happens when a magnet is placed near a cathode ray. The light shown on the screen changes depending on the location of the magnet. This is because the force vector is the cross product of the velocity vector and the magnetic field vector.

In this picture we showed what would happen when the magnetic field was brought in at different locations. The Force vector was always normal to the velocity vector and the Magnetic Field Vector. From the direction of the arrows you can see that the the Force vector is the cross product of the Field and Velocity vectors. 

In the above picture we were able to determine the acceleration of a proton by first finding the force created by the velocity and magnetic field vectors and then plugging it into Newton's second law equation.

In this picture we determined what courses velocity and force vectors would take after interacting. We also derived an equation for the magnetic field and we solved with given frequency for the magnetic field on an electron.

In the above two pictures Professor Mason showed us what would happen when wire, which was charged, was also subjected to a magnetic field. In the top picture he only had a wire setup, and after the charge was turned on, the wire would jump toward us. This was because the cross product of the current and field was toward us. But in the bottom he had a circular wire above the magnet.

We were tasked with answering the question of what would happen to the circular wire setup when the current was turned on. We made a diagram on the bottom right of the board. We knew that the current would be going clockwise and we knew that the magnetic field would be pointing up. As a result we knew that the setup would turn 90 degrees in a clockwise motion away from us, and then stop. This turned out to be the correct answer.

We derived that that Force was equal to the cross product of IL and B, with L and B being vectors. I is not considered a vector in this setup.

In a situation where the magnetic field is normal to a current we find that the sum of the force vectors is 0 Newtons, since each vector has another vector which cancels it out.

We were asked to find the force at each of the locations on the half circle. We broke the circle up into 15 sections and plugged it into excel with the formula I*L*B*sinTHETA, L being the radius, and were able to come up with the force at each section of the semicircle.