Tuesday

Periods 3-4, 8-9:

EM induction is all about magnetic flux. Remember Gauss says electric flux = (E-field)(area), so magnetic flux = (B-field)(area) = BA. And one thing we will see with a number of devices is that if there is any change in magnetic flux, then a voltage is turned on if the object is a conductor. This is like when you move a magnet through a solenoid, and voltage turns on. If the magnet is till, the voltage turns off. We'll figure out why this is, but nowadays we call this rule Faraday's law:
     induced voltage = "electromotive force" = emf = d(BA)/dt

So the faster you move a magnet through a wire loop or solenoid, the more voltage is induced. Faraday called this 'electromotive force,' or emf, and many still use this term. There are 2 main ways to change flux:
i) have a constant B-field but move a metal loop (changes the area where the magnetism goes through), BdA/dt
ii) hold a metal loop still (constant area) and change the magnetism, AdB/dt

Please check out the two videos:
One common, and perhaps strange, example of magnetic flux can be seen here.
Description and examples of emf = BdA/dt can be found here.

In the packet you get in class, for flux please try Ch. 27 #11, 13, 14 (p. 5). A packet for emf = BdA/dt is in our EM Induction folder here. See if you and a study group can talk through the 1981 problem on page 5 of the packet.


Period 6:

We are starting static electricity. The biggest example is lightning, which we may see later today with some storms coming in. Check out this video, and take notes, on some ideas as to how lightning works.

Then, search on YouTube 'static electricity.' There will be all sorts of video options. View a few and look for your favorite demos/experiments to try with static electricity. Write down your 2-3 favorites that you'd like to do in class, and be sure to include materials and procedure. We'll check them out tomorrow and plan on doing some, and figure out how it all works!

Tonight, read and take notes on pages 541-548.