We practiced more on our two right hand rules, one to tell us how magnetic fields wrap around electric currents and one to tell us the direction of the force exerted on moving charged particles and currents. We also saw the fundamental relationship that we exploit in mass spectrometers, tools used to identify unknown substances. In which direction does the magnetic field point in this mass spectrometer in order to cause the positively charged particles to curve to the left as shown. Note that the particles start their journey from the right side of this mass spectrometer. [Answer: Vertically downward]
Assignment:
Because of our CPR training, Periods 1, 3, and 5 have been covered this week by the entries for Monday and Tuesday. Not so Period 6. Today we will turn in our handouts from last week (2 sheets) and push ahead on useful mathematical relationships involving magnetic fields.
Assignment:
We marshalled our data and created our graphs. It seems most everyone got a direct proportion. Do you know how a plot of a direct proportion is different from just any linear relationship?
The final lab note will be due on Friday. Your graph should be correctly constructed and labeled. If you have a linear plot, you should include the trendline and its slope-intercept relationship with proper units on the numerical value of the slope! We sought to find out how the strength of the magnetic field of a solenoid depends on the amount of current flowing through it. When you are done not only should you get an understandable relationship from your plot, you should also have a good idea of how to sketch the magnetic field of a solenoid using magnetic field lines.
Assignment:
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 in the loop shown below. Can you? We also reviewed the right hand rule for forces exerted by magnetic field on moving charged particles and on electric currents. Can you figure out the direction of the magnetic forces on the particle at the moment that it enters the magnetic fied and on the current in the diagrams above? We also saw this excellent 60-year-old video with sharply dressed MIT physicists! 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: Here's our assignment for Friday. Just work on the first two items unless you want the challenge of finishing it on your own. The information is in Sections 3 and 4 of Chapter 20.
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 introduced the magnetic field today. The strength and direction of a magnetic field is represented by the letter B. The source of all magnetic fields is moving electric charge (and, as we will see later, changing electric fields).
The relationship between the directions of electric currents and the directions of the magnetic fields they produce is described by the Right Hand Rule (RHR) that we introduced today. We also listed six ferromagnetic elements. There are also many ferromagnetic compounds, many containing rare earth elements like neodymium and samarium. Interesting stuff. Assignment:
We discussed the lab report that is due tomorrow including how to find the time constant for your circuit from the charging and discharging graphs. We also took a post-test that is used only for designing instruction for future students. Thanks!
Here's the information about the RC lab that we did and for which your lab report is due tomorrow. Note that we only found how Vcap depends on time. We did not vary R or C. So your purpose includes only that first independent variable in the list of three in the lab information. We built a circuit with an integrated circuit included in it. The point of the circuit was to make two LEDs flash alternately, changing the flash rate by changing the RC constant by replacing the capacitor with a different capacitor. We had some successes and some blow-ups!
On this happy Valentine's Day, we dispensed with our RC handout, problems Ch 19 P: 35, 36, 37, and we set the stage for tomorrow's circuit building on a breadboard with an integrated circuit (IC).
Assignment:
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Physics IIMr. Swackhamer Archives
May 2019
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