Freeman Dyson has died at 96 years old. He has been a creative and productive physicist, and I always enjoyed reading his work. In his early career he worked on the nature of fields like electric fields, for example. That branch of physics is called Quantum Field Theory, and it is amazing.
Mia Dyson says her father, at the age of 96 still regularly went to his office at Princeton University. "You could tell that the world was a beautiful place through his eyes, and somehow understanding all the formulas and the natural laws and all the mysteries he had plumbed through the study of physics, that it only grew more and more beautiful, the more he understood." RIP We worked on understanding the Right Hand Rule for forces on moving charged particles and electric currents today. I'm hoping that you are fairly comfortable with them now. Of course, we will be using them in our work, so we can really become adept at using the RHR! Can you figure out the force experienced by the negative ion at the moment it enters the magnetic field shown in the diagram above and on the left? How about the direction of the force felt by the conventional current in the rightward-directed magnetic field shown above on the right?
The two right hand rules were featured today as we tried our best to get a grip on what nature is like. The first right hand rule we encountered was the right hand rule for magnetic fields created by electric currents. As an exercise, you should be able to figure out the direction of the magnetic field created by the current inside the loop shown below. Can you? Can you figure out the direction of the magnetic force on the particle at the moment that it enters the magnetic field in the diagram below? You should be able to use magnetic field lines to sketch a representation of a bar magnet's magnetic field by now. You also should be able to use the right hand rule for currents to sketch the magnetic fields produced around electric currents. Today we dealt with forces that magnetic fields exert on moving electric charge. It's a weird force, one that we wouldn't have predicted, and it is described by a mathematical tool, the cross product: Can you figure out which of the particles that trace out the paths shown below are positively charged? The magnetic field that made the charged particles curve as they traveled along is directed into the picture. The initial particle that caused all the havoc you see entered the picture traveling from bottom to top, and that's the general flow of things here (as a result of momentum conservation).
We saw where the mathematical relationships for charging and discharging come from. We used our calculus to work it all out. You should be able to determine the time constant for each plot. Can you?
Today we did an experiment in which we charged up a capacitor, and then discharged it. Our goal was to see how the voltage across the capacitor depends on time.
Capacitors are on the front burner now. We've waited until now to deal with them all at once.
A good, practical resource for learning about capacitors is:
Assignment:
|
Physics II
Mr. Swackhamer Scottsdale Preparatory Academy Archives
March 2020
Categories |