## 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:

## Wednesday, January 20, 2016

### Could be a New Planet in our Solar System, well beyond Pluto's orbit

There have been inquiries into a 'Planet X' (where X would mean a 10th planet) for centuries, sometimes by those who had folly-type claims to others being serious astronomers, but now there is calculational evidence there should be something pretty large, about the size of Neptune (an order of magnitude more massive than earth) that orbits the Sun once every 15,000 years! Check out this article from Science. There is, as of now, no direct observational evidence for the planet, but calculations show how the gravity of something this size, at that distance and with that period, has perturbed other objects in the outer solar system. Cool example of how theory and simulations can lead to exciting, possible new discoveries - of course, we still need to actually see the thing before we should completely accept it!

### Python Activity for Today: Looking at data for Dark Energy

Up to now, we have begun to learn some basics of Python using Codecademy, then we began to use Python to develop simulations of a bouncing ball (how to put equations of motion into a program) and a double pendulum (which we cannot do with pencil and paper, and included a focus on making graphs and animations in a program). Today, we will use a Python program to analyze data, which happens to be the data used to determine the acceleration of the universe and prediction of Dark Energy.

The activity for today is here. We will open Canopy to do this, as in the past.

If you are interested in the physics behind all this, dark matter and dark energy are not the same things. Dark matter is a term used for matter we cannot see. It could be a mix of several things, such as 'ordinary' matter and some new types of matter, that we cannot see directly but presume it is there due to its gravitational effects on things like galaxies. Dark energy is a term used for whatever it is that makes the expansion of the universe accelerate - we do not know what dark energy is. Of course, there is the scientific model for how the universe began and why it is expanding in the first place, the Big Bang.

Minute Physics video on Dark Matter.
Minute Physics video on Dark Energy.

## Tuesday, January 19, 2016

### Band Theory video

This is just a very basic introduction into band theory, and conceptually how energy 'bands' form. The basic point is that this occurs when we have numerous atoms or molecules interacting with each other. The individual electron energy levels we are used to from the Bohr model (for a single atom) are perturbed and slightly shifted when in the presence of another atom, and with a bunch of atoms interacting, all these slight shifts begin to look like a continuum of energy rather than discrete, quantized energy levels. I hope this helps.