12th of May's Class
We started the day with a visualization of what happens to the arrangements of charges within a magnetizable material. The reason that a metal can behave like a magnet when is due to the arrangement of the charges on the right side of the image above.
Since the positive and negative charge are pointing at different ends, they do not cancel each other out. There is always a magnetic field, however, in the case of the unmagnetized metal, the orientation of the charges cause the magnetic fields to cancel each other out due to their random arrangements, hence the metal could not behave like a magnet.
Professor Mason then gave us a demonstration about demagnetizing a magnet. First, he magnetized a paper clip using the horseshoe magnet (which can be seen at the bottom left corner of the image above). Then using a small flame thrower, he heated up the paper clip. After letting it heat up, the paper clip loses its magnetism.
The explanation behind this phenomenon is that the charges that were arranged in an orderly manner, to generate magnetic field, absorbed kinetic energy from the heat. The charges then started to move about randomly within the metal, and therefore reverted back to its unmagnetized state.
We were then asked a question about the torque that occurs in a wire that is shaped like the outline of a hammer (It is located at the bottom half of the picture above, written in green marker).
If a current was to be run through the circuit, with magnetic field moving in the direction of a positive vertical axis; what would the torque be at each of the segment of wire. The formula written above is missing a sin(theta), which would help to explain that those segments of the wire that is parallel to the magnetic field would have 0 overall torque. The direction of torque is dependent on the direction of the current relative to the magnetic field.
We were then given a question from the powerpoint slide, however, since I did not manage to take a picture of that in time, and the lecture file is not yet uploaded to the website, the question that accompanies this solution is forgotten. However, the essence of this question is a practice in finding the torque of a looped wire. N in here represents the number of loops of a wire. With this, we come to understand that torque is cumulative.
The image above is the insides of a motor. Although it cannot really be seen, there are a few key components to a motor: Armature, Commutator, Brush and Magnet. Armature is the part that rotates, Commutator reverses current at certain intervals, Brush conducts current between rotating parts and stationary parts.
We were then to have a hands on experiment with constructing a simple motor from a set that had already been given to us. This is what it looked like:
After setting this up, we were supposed to follow the conditions stated in the Lab Manual. Below is the record of the results of our experiment:
The black boxes on the right is the record of when there are some things that are happening. The N and S represents the position of the Magnet; the upper and lower half of the black boxes record the difference when the direction of the current is switched. The motor would not work if the magnet has the same pole on both sides, and also when there are no magnet involved at all.
After that, we were to make an even simpler motor that looked like this:
The motor looked like a blur sphere in this picture as it is taken when the motor was functioning. Below is a video of it in action:
A question was then given to us, to derivate an equation:
The image right above shows the steps to find the Hall voltage.
Next, Professor Mason gave a demonstration about magnetic field. In its initial condition, all the compasses on top of the cardboard boxes to the left of the image points to the North. A current will be made to pass through the metal pole sticking out of the cardboard box. We were supposed to predict the outcome of this demonstration, where would the compass be pointing?
As it turns out, the compasses point in a circular manner around the metal pole. The professor then repeated the experiment, but this time the current was reversed. The same thing happened as in the earlier demonstration. However, this time the compasses are pointing in a counter rotation to the earlier demonstration.
The image right above this is a circuit in which Professor Mason wanted us to practice our ability to read and predict the direction of the vectors involved, Current, Magnetic Field and Force vector.
No comments:
Post a Comment