4 Chem/Phys Remote Class - Practice sets for EM Induction

Happy _____day, everyone, depending on the day you see this!

If you missed Tuesday's 10 am class session, click here for the video recording.

Electromagnetic induction: This is one of the greatest discoveries in physics history, if not science history, since it helped create our modern electrical civilization. The primary players in this were Michael Faraday on the experimental side, and James Clerk Maxwell on the theoretical side. You've already 'discovered' the gist of em induction in our magnet lab a couple sessions ago - I asked you to play with magnets and a solenoid to see if you could create voltage using nothing but the magnet.
How did you do it?

You had to move the magnet around inside the solenoid. So some combination of coils of wire, a magnet, and motion allow us to create electricity. I will demonstrate this in Wednesday's Zoom session, if you are able to join us. I brought some equipment home so we can still at least do demos.

We are starting with Packet 1 (you either have a hard copy or it is in the EM Induction folder of our school site). This introduces magnetic flux and Faraday's law of em induction.
Note that I will still be giving recommended practice sets, and we have relevant videos for each concept and type of problem. I hope you will still try them, and discuss with any study group or individuals as you normally do - but remotely!! Call or Face-time or use other social media platforms, or use Zoom or Skype to meet with each other remotely; we strongly discourage you from meeting in person. The whole point is social separation for the next couple weeks, not only to protect you, but to prevent the spread to those who have contact with older individuals who are much more susceptible to this virus than you probably are. Send pictures/video of your work to me or each other when stuck so we can discuss, or ask questions when we have our Zoom sessions. I'll be checking email a lot, as usual.

*With 'Act of God' days, teachers are not taking attendance. Even if we were to grade work and enter into the gradebook, it will not be counted by the school. So while this is the case, I hope you will keep up with your classes. Be curious! Enjoy learning! When you go to college, you will still be expected to know some of this stuff! Complete what you started, and give it your best shot! And at this time, we don't know the status of any AP exams.*

Magnetic Flux
Faraday's law revolves around magnetic flux. From Gauss's law, electric flux = (E-field)*(area it flows through); so same idea, magnetic flux = (B-field)*(area it flows through) = BA.

But what Faraday discovered is that if one changes the magnetic flux flowing through the area of a wire hoop, voltage is turned on, or induced. That's it!! Make a system where the magnetic flux through wires is changing, and you can power things with electricity. This is an electric generator, and the basis for how power plants work all around the world! Related to it are electric motors (think about how many electric motors are in your house and in your life).

Faraday's law:   Amount of induced voltage = emf = -d(BA)/dt

Here, emf is what he called electromotive force...it is just voltage that gets turned on when the magnetic flux changes. We will study the 2 main ways to change the flux:
i. induced voltage = B dA/dt, which is Packet 2
ii. induced voltage = A dB/dt, which is Packet 3

For Wednesday:
- Watch a short video on finding flux through a loop of wire.
- Try Ch. 27 #11, 13   and  Ch. 29 #1, 7.  These are on pages 5 and 6 of Packet 1. Answers are in the back of your textbook, and check examples in chapters 27, 29 that are similar if you get stuck. We'll go over these and introduce Faraday's law in Wednesday's Zoom session.

Thinking ahead:
For Thursday and Friday, we will focus on Packet 2. This will be the case where we leave the B-field alone, and move things around so that the flux area changes (this is how generators in power plants work). We will focus on videos for a moving piece of metal in a magnetic field, moving a metal hoop through a B-field, and dropping metal hoop through a B-field. Believe it or not, these cases will be the same mathematically as an old favorite, air friction!!  😉😨

Note there are worked examples/notes in packet 2 that go along with the video examples. And we will be trying the AP problems in Packet 2. Don't forget we have AP solutions on the school website, in the AP Exams page, in the AP Exam Solutions folder. You need to be logged in your eths202.org account in order to access these solutions.