5/14 Faraday's Law and Magnetic Force

Professor Mason uses a Halls Effect sensor to find the magnetic field inside the classroom. When he spun around the classroom for the 10 seconds Logger Pro took data for, it showed a sinusoidal behavior. This is because when mason spins basically spinning a compass around and the needle's behavior is what we observe on the graph. 

We made a copper coil and used the same sensor used to measure the magnetic field of a coil of 1 loop of wire up to 5 loops of wire. Our measured magnetic field is shown as this graph

We drew a current going down 2 wires that are in parallel and were asked to find the force vector created by their magnetic fields. We found that with the right hand rule, the force cancels in the middle and goes in through the board on the left and out through the board on the right.

 

In these two pictures, Professor Mason uses an ancient device to measure the magnetic field when moving a metal rod at inside a coil of wires. We observed that when there was no movement, there was no magnetic field. 

In the above 4 pictures, we created a magnetic field that would induce a magnetic field on the object we placed around it. We tried this with 3 different types of material, wood, copper, metal. We observed that with a wooden ring, nothing would happen. The wood is not a conductor therefore there is no way for the current to travel through it. We then tried copper, a very poor conductor. We found that the copper ring jumped a bit but because it does not conduct the current well, it only did a small jump. We then tried 2 different metal rings, one thin and one thick. The thick one jumped up a bit and stayed floating. The thin one flew off the tube. Because metal is such a good conductor, it was able to conduct a high enough current to create a magnetic force in the downward direction. The thin metal ring flew off because it was just as good of a conductor but was lighter so the magnetic force larger.

We calculated the flux of 2 plates oriented differently. The flux from the magnetic field when plate is parallel to the magnetic field is 0 and the magnetic field when the plate is perpendicular to the magnetic field is the magnetic field times area. The actual formula is the dot product of the magnetic field and the area. We were then asked what elements could change the magnetic field. From our experiments, we answered the 4 in orange. 

We have 2 tubes, one aluminum tube and one acrylic tube. This experiment was to see what would happen if a magnetic object was dropped through the acrylic tube and the aluminum tube.

This is our results from the previous experiment. We found that when the magnetic object was dropped through the aluminum tube, it went through significantly slower than it did through the acrylic tube. Even though aluminum is a poor conductor, it still managed to create a large enough magnetic force from the magnetic object's velocity to slow it down significantly. We then derived its relationship.  

The top graph shows a magnetic field graph vs. time and the bottom graph shows an emf graph over time. We found them to be sinusoidal. If we were to interpose the graphs, we would get the x-axis. 

5/12 The Magnetic Field of a Current

Professor Mason used a magnetized paper clip to demonstrate how a piece of metal loses its magnetic field when its heated. Heating the molecules causes the poles to realign themselves back to before they were magnetized.

On the right, we have pictures of how the poles on a piece of metal are aligned when they are magnetized and when they are not magnetized. The magnetized piece of metal had all their poles aligned so that the north and south poles were pointing in the same direction. The non-magnetized one has poles pointing in all directions so the poles magnetic field cancels each other out. We were then asked how we could destroy the de-magnetize the magnetized metal. We said that if you hit it really hard or heat it up really hot, it would realign the poles back to pointing in all directions.

This is the sample motor that Professor Mason gave to each group. We noticed that for the coil to spin fast, it had to be as close as possible to the magnets on each side. They were so close that you could notice scratches on the magnet. We also noticed that it is better to have a north and south pole magnet on opposite sides of the coil to keep the coil spinning fast.

This is our motor created with a coiled piece of wire, batteries, a magnet, and a closed circuit. We found that the most difficult part of having the engine run consistently was to have the coil as close as possible to the magnet underneath it. This way we can shorten the time that the coil is in the part of the spin where there is no torque, and the momentum can easily push it to keep spinning. We also found that if we have bends on the ends of the wire, it would cause a torque in the direction of the bend causing the coil to not spin smoothly. Straightening them made it spin smoother but made it easier to fall out.

We discussed the different components that are required for a motor to run. We found that the thing that is most likely to break in a motor is the brushes as they are made out of thin plastic and are frequently used to change the direction of the motor.

The above 2 pictures are from an experiment we did if we had a current going through the metal pole in the center of a box surrounded by compasses. We found that the current produces a magnetic field causing the magnets to point in a counter-clockwise direction around the metal pole. This matches our right hand rule along a current.

This is a problem we did in class of a current going through the pattern shown above. We were asked to find the force in between the wires at the very top. We found that with the right-hand rule, the magnetic field caused by the current is going through the circuit at that point is going into the board.

We drew our predictions for the compass experiment as well as the force between the wires at the very top. From these 2 experiments, we derived equations that related the magnetic force and the force due to the electric field. 

5/7 Magnetic Fields

We were asked to draw arrows that indicated the direction of the magnetic field at different points on this metal bar.

This is our representation of how the magnetic field looks around the metal pole. We found that we could use our old formulas that had Electric Field in it and replace it with a new variable B, the magnetic field and we could replace charge, q, with the number of poles, p, . Our old formula with electric field is charge / epsilon but since the net amount of poles in the magnetic field is 0, we can say that the integral of BdA = 0.

This is a visualization of how the magnetic field behaves around the metal bar. We see that the magnetic field looks like the patterns on a pumpkin except on the top and bottom where the arrows don't circle back to the metal bar and keep going.

We were asked to make a prediction of how the piece of metal in the middle of the magnet would behave once it was charged. We found that it didn't matter if the charge was negative or positive, only the direction of the current mattered. 

We were given a problem that asks what the force is on each direction of the metal plate if it lies on the xy-plane and a magnetic field is going straight through it on the z-axis. We found that since the magnetic field is perpendicular all force vectors on the metal plate, the net force was 0N.

We derived a formula to find Force and found that force = qV x B. Since we know that current = charge / time and velocity= length / time, we can interchange q and v with I and L depending on the given information. 

This is an example of how a Cathode Ray Tube behaves when their is a strong magnetic attraction/repulsion near the tube. Because the magnetic force from the magnet is strong, the electrons inside the tube are attracted/repelled toward/away from the magnet. Originally, the green dot was at the center of the screen but because of the magnet, it has shifted slightly to the left.

We draw a diagram of how the inside of a Cathode Ray Tube works and found the resultant force vector if there were a magnetic field being directed at the electrons from a certain direction. We used the right-hand rule to determine the direction of the force and found the dots displacement if it started at the center of the screen.

We were given a problem to find the acceleration of a proton in a magnetic field with the given information. 

This is 2 different problems that we were asked to find the force of. In red, the metal plate is parallel to the direction of the magnetic field and we found that the force on the top and bottom were 0N and the force on the left and right canceled each other out resulting in a net force of 0N. In green, we were asked to find the torque of the metal plate if the magnetic field is going through the z-axis and the plate lies in the xy-plane. We found that the force on the left and right were 0N and the force on the top and bottom were going in opposite directions. This caused the plate to spin clockwise. 

We were given a problem that asked what the different forces were at 15 different segments of a half circle. We were given the radius, magnetic field, and the current. We found that at the rightmost and leftmost parts of the half circle, the force was 0N and the force is greatest at the center. This makes sense because the magnetic field is tangential to the force vector at the left and rightmost points and is perpendicular at the center. 

5/5 Oscilloscope

This is the Cathode Ray Tube we examined in class. We were told that inside the tube, there are 4 plates that help guide the electrons to the end of the tube. The material the end of the tube is made out of turns the fired electrons into a color we can visually see, green. The switch Mason has his finger on changes the orientation of the plates inside causing the electrons, or the green dot, to shift positions.

This is with the Cathode Ray Tube on. We see that the electrons have been fired to the center of the Cathode Ray Tube.

We were asked to predict how the Cathode Ray Tube on the Oscilloscope would change based off a change in voltage from a DC supply, we said the output would be shifted upwards and were correct because the y-axis is in units of voltage and adding voltage would just increase the y-intercept. We then derived formulas for a velocity of an electron given time and length of the magnetic field. We found that using kinematics, we could find that the velocity of the electron is simply the length/time

We used speakers to help determine how frequency sounds at different hertz. We found that the older one gets, the smaller the frequency one can distinguish. 

The above pictures are from our lab with the Oscilloscope.

This was the Mystery Box part of the lab that we came in on Friday to complete. We found that the yellow plug was just for grounding so when whenever we had a combination of two plugs consisting of yellow, the voltage and wave shape was the same as the combination without yellow. 

These were are conclusions as to what the different plugs were.