## Tuesday, January 26, 2016

### Classes for Tuesday

Periods 1-2, 8-9

Today, check out an introduction to what we call Ampere's law. This is used for figuring out magnetic field behavior much like what we use Gauss's law for electric field behavior. In fact, Ampere's law is used for 3 cases: a long, straight wire with current; a long solenoid (no ends); and a toroid (donut with wire wrapped around it). Take notes on this video, and we will come back to it Wednesday.

The big thing for today is the lab with cathode ray tubes (electron beams). You are going to use the large circular electromagnets, called Helmholtz coils, to generate a magnetic field that will affect the electrons. Follow along with the lab and take it in order. You can and should take out the tube for a couple of the parts of the lab.

DO NOT do anything with the wooden box, which is the power supply for the cathode ray tube. Things are all set to go, just turn it on and wait until you see the dot where the electrons are hitting the surface of the tube. When you are measuring the distance the electrons move for a particular voltage (measure this with the multimeter), measure how far the center of the spot moves.

When you try to see the effect of an AC magnetic field, move the cables on the green power supply (which is generating your B-field) to the yellow terminals.

Try to do all parts of the lab except for #7 - we will try both DC and AC fields on Wednesday. Try Ch. 27, #63 for Wednesday.

Periods 3-4

Take notes on two Gauss's law videos. One is for conducting materials (i.e. metals) that have a static charge. One is for NON-conducting materials with a static charge. The big difference is when you are inside the material. For conductors, there is NO ELECTRIC FIELD inside the material (you are safe inside metal, like the birdcage idea, called a Faraday cage). Any static charge sits on the outside surface of the metal. For NON-conductors/insulators, charge is spread throughout the material, and we have a charge density (charge/volume), much like mass density in chemistry.

Try to make as much sense as you can, and see if you can apply any of this to two examples in the packet from yesterday: