Links Useful to Tuesday, Feb. 28

Happy Tuesday, one and all!

For Periods 1-2, 5-6, 8-9:

It is time to start digesting Biot-Savart for magnetic fields, due to real wires. Unfortunately, real wires do have ends, and this means Ampere's law does not always give a good enough approximation for one's needs. Check out two videos that will take you through B-S for straight wires with ends, and one for a loop of wire with a current flowing (like the Helmholtz coil we used in the CRT lab last time).

Note that there is another video showing an example of B-S with multiple wires and currents, where we try to determine the B-field at some point from the two wires. If you need a review of B-S for moving point charges, there is a video for this here.

After watching the first two for wires, see if you can figure out the practice problems: Ch. 28 #59,60 for point charges (on page 7 of packet), and the collaboratives for wires on page 9 of the packet.


For Period 3:

Let's check out one video on defining the electric field some more. Take good notes on this since it will help with some of the problems we have coming up. Then, a second video will get into some examples of how to work with our formula for the electric field, E = kQ/r^2; you should take good notes on this one, too.

We will come back Wednesday and take a look at some examples of finding electric fields, and also electric potential, which is what we will call voltage.

We will try chapter 21, #66, 67, and 69; copies of these are in the packet you receive today.

Python Lesson for Wednesday

Hump Day!!!

Last week Fani was able to show us the importance and huge role of computer programming and simulations in science research. It is essential, and it is now a fact of life that if you do anything in STEM (and most other fields outside of STEM, as well), knowing even the very basics about what a program is, and how to manipulate existing code (not necessarily writing your programs from scratch) is invaluable and, frankly, expected.

We will do a bit of coding in Python throughout the semester, to expose you to this area of work.

The lesson for today is here.

First thing: In the computer lab, log into your student account and open the program Canopy. Do not click on it more than once - it will take several minutes for it to boot up. Canopy is something you can download for free on a home computer, and allows you to write and run your own Python scripts.

Earth's magnetic field articles

Check out a Scientific American article online, as well as a NASA article on reversals. Last but not least, a NASA article about the way the earth's magnetic field is constantly moving around and changing!

From your article notes and the video notes in class, summarize how scientists know all this, especially if there were no scientists around 800,000 years ago when the earth's field last reversed!!

Momentum

We will try to bring back momentum, p = mv, from last year. Keep in mind two of the big things: it is a vector, and it is conserved.

To see WHY it is conserved, check out this video and take good notes.

Then, check out perfectly inelastic collisions that combine momentum with energy conservation, using something called a ballistic pendulum. Again, take good notes since it will help with some homework problems.

Ampere's law introduction

Check out an introductory video on something called Ampere's law, which has to do with the production of B-fields from 'long,' straight wires, long solenoids, and toroids. Ampere's law will be similar to Gauss's law for E-fields in the past.

For Today

Happy Friday, everyone.  :-) 

Periods 1-2, 5-6, and 8-9:

Check out magnetic forces on charged particles. A moving charged particle produces its own magnetism, which means magnets will make a force on that moving charged particle. This is where cross products start.

The magnetic force is F = qv x B.  Remember how to do the math for cross products (the 3x3 determinant thing), and that for A x B = C, the magnitude of C is C = ABsin(theta).

Check out two videos, one on the magnetic force on particles, and the second on an application called a mass spectrometer (along with a so-called velocity selector). Take good notes since you will need them for the practice set, which is the book problems and the first AP problem in the new packet you are receiving.


Period 3

We will be going into magnetism, so check out videos on this. First, watch and take good notes on an introduction to magnetism. A second video is on magnetic force. We will begin a lab with magnets on Monday, where you will get to begin (literally) feeling these forces, sometimes attractive and other times repulsive.

For practice and to begin thinking about magnetic fields, try the sheet you will receive. Use the side with diagrams to try and answer the questions.

Scientists can watch an 'optical boom' with photons moving through material

For the first time, scientists can use high-speed videos (we are talking over one trillion frames per second...crazy short time intervals!) of a pulsed laser beam moving through a gaseous material to see the optical equivalent of a sonic boom. A sonic boom happens when a sound producing object like a plane moves faster through air than sound waves - we get a cone shaped structure of sound. The video in the link has a clear image of the cone-shaped pattern of light as the laser pulse moves at different speeds in a material compared to a gas layer that is also in the system. This is really cool!

Here's Problem Solving/Engineering 21st Century Style - Agricultural MRI from Above

What a very cool application of high resolution photography, drones/airplanes/satellites, and computing - a UIUC professor has started a company that may be revolutionary for farmers to be able to identify issues in large farm fields (hundreds or thousands of acres). The company takes large numbers of photos of the farm fields, and then uses software it developed to identify even small areas within the field where there is an issue with disease, weather damage, lack of moisture, weed growth, and so on. In the past this has not been possible, and certain types of issues could spread to large sections of a crop before it was known - crop yields can only be improved using this technology and diagnostic technique. I personally love seeing creative, multidisciplinary solutions that can help make the world just a bit better!

Mechanics Semester Review

Here is a list of topics for our final, the second week back from winter break:

Basics:
Vector algebra - vector addition, multiplication (dot and cross products)
Derivatives - finding them; what does it mean graphically; instantaneous values
Define v = dx/dt; a = dv/dt
Antiderivatives - finding them; what does it mean graphically
Motion graphs

Kinematics:
Constant acceleration equations, how to use them in a variety of problems
Free fall
Relative motion (e.g. boat going across a river)
Projectiles

Newton's laws:
Know them by number; conceptually what do they mean? Examples.
Finding resultant forces (vector addition)
Equilibrium, balancing forces in multiple dimensions
Applications of Fnet = ma, all types
Tension, friction, on inclines (gravity triangle), springs
Systems problems, such as multiple blocks tied together
Circular motion, how to set up mv^2/R in problems; horizontal vs vertical problems
NON-constant forces and accelerations
Air friction, f = -kv; derivation of v(t); chain rule
Gravity - Newton's law of universal gravitation; Einstein's thoughts on warped space-time
Orbital motion - orbital speed, Kepler's laws; Binary orbits

Energy:
Conservation law
Different types, conversions of energy
Work redefined as an integral; work is the amount of energy transferred between objects
Using work and conservation to solve a variety of problems, especially with speeds and non-constant forces
Potential energies (gravity, springs)
How to do gravity the right way with energy, U = -GMm/r; what does - sign mean?
Potential wells - U-x graph vs F-x graph; positive force vs negative force
Gradient, F = - dU/dx; what this means
Escape velocity; Schwarzschild radius
Power
Special relativity implications, Einstein's energy equation

Resources:
Videos on most of the topics above. For practice multiple choice, the SAT II site has notes, sample questions, and explanations on all these topics. There is a Learn AP Physics C site, with practice questions. We have our AP Exams folder (but you must be logged in only on your eths202.org account).  Note there is a multiple choice folder, with hundreds of practice questions. There are review sets in each of our unit folders. Read up on any topic and check out dozens of worked examples in Chapter 1-7, which is what we have covered so far. You have your old quizzams and solutions, homework sets, and labs.

EM Semester Review

The main topics are listed below. Keep in mind this is covered in chapters 21-26. There are numerous worked examples and odd problems we can try, along with chapter review pages. There are videos on just about every topic. There are AP Free Response Problems and Solutions  (including a multiple choice folder); be sure to be logged in with your eths202 account for access. There are review sets in each topic folder on the school web site. There are practice problems and notes on the SAT II website. There is practice materials at the Learn AP Physics C site. Get into a study group. Come in for AM Support or lunch periods. Review old quizzams, HW sets. Review the essential questions you've received for each unit, and the objectives file. Review the equation sheet. Lab questions and concepts are fair game. 

Topics

Electrostatics

• Properties of charge
• How do you charge objects? Induction vs conduction

• E-field and Potential for point charges

• F = qE and U = qV
• Work done when charges move around

• Energy conservation to find speeds
• Projectile example

• Equipotentials

• Non-gauss examples, integrals
• Sticks, rings, partial rings

Gauss's Law

• What does it define?

• Why does only 'charge inside' matter?

• Why only the three shapes that we use?

• Thin shells
• Materials: what are physical differences that make them have different properties? Band theory. 

• Conductors

• Nonconductors, uniform density

• Nonconudctors, NON-uniform density

• Combinations of materials in layers

• Finding electric potential for layers

Circuits

• Conceptually how do we setup currents in wires?

• What is resistance? What does it depend on?

• What is current? How would you find charge?

• What is power? How would you find heat energy from resistors?

• Series vs parallel
• Resistance
• Capacitance
• Conceptually what is same, different
• How to find current in each resistor

• Ohm's law, Kirchhoff's 2 rules

• Multi-loop

• Capacitor only circuits
• How to find charge on each

• RC circuits, series
• Conceptually what is happening?
• Can you derive q(t), i(t)?
• Charging
• Discharging