184_projects:s20_project_15 [Projects & Practices in Physics]

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===== Project 15 =====
==== Project 15A: Sending signals ====

You are able to use your successfully MacGyver'd metal detector to track what the EM-boar tigers have left behind and find your trapped team members. But it is not only your team members you find. It is the EM-boar tigers base of operations. More important than rescuing your team members you observed something in their lair that effects the whole of humanity and needs to be communicated immediately. You estimate there is about 1 hour and 50 minutes to figure out a way to send some sort of E&M signal out for rescue before the EM-boar tigers realize that you are planning an escape. (What will that signal be??? You decide.) Due to the sensitivity that EM-boar tigers have to E&M waves, you only have one chance to send the signal before they realize what is happening and close in on the team. You will need to make sure that the attempt will work. You have a small metal ball that can be charged up 1e-6 C without discharging in air. You've found a piston that can shake the ball a total distance of 2cm, but at nearly any frequency you need. Your team decides to create a model of the signal to determine how best to orient the setup, how much charge to dump on the ball, and how quickly to shake it. Your group has already started setting up the code.

<code>
GlowScript 2.6 VPython

## Objects

charge = sphere(pos = vector(0,0,0), radius = 0.001)
charge.v = vector(0,0,0)

## Constants and model parameters

q = 1e-6
k = 9e9
mu = 4*pi*1e-7
mofpi = mu/(4*pi)

## Set up time parameters

t = 0
dt = 0.1


## Create list of arrows that encricle the charge
## Each location has two arrows: one for E and one for B

N = 20
theta = 0
dtheta = 2*pi/N
R = 0.02
ArrowList = []

while theta < 2*pi:
    
    Loc = vector(R*cos(theta), R*sin(theta), 0)
    
    ArrowList.append([arrow(pos=Loc, axis = vector(0,0,0), color=color.cyan),arrow(pos=Loc, axis = vector(0,0,0), color=color.magenta)])
    
    theta += dtheta

## Calculation loop

while t < 1000:
    
    rate(100)
    
    ## Charge should oscillate
    
    
    ## Loop through arrows to make E and B vectors
    
    for Arrow in ArrowList:
        
        r = Arrow[0].pos - charge.pos

        E = vector(0,0,0)
        B = vector(0,0,0)

        Arrow[0].axis = E
        Arrow[1].axis = B
       
    t = t + dt
</code>

<WRAP info>
=== Learning Goals ===
  * Make predictions for the electric and magnetic fields from a moving charge over time
  * Model (using VPython/Glowscript) the electric and magnetic fields from an oscillating charge
  * Explain the effect of changing a variable on your model of the electric and magnetic fields (i.e., what would you expect to change if you changed the magnitude or sign of the charge)
</WRAP>



==== Project 15B: Design your own review ====
Your group is to design two exam problems that can be used as practice problems by the class. As a reminder the topics for the final exam include:

  - Electric fields (including force, potential, energy) from charges of different shapes
  - Circuits
  - Magnetic fields/forces
  - Induction

Your design should include both the **problem statement** and the **solution** to the problem. Imagination is a plus. Try to come up with a context for your problem (not just "There's a moving charge") and follow the typical format for exam questions (multiple parts, some calculations, some concept questions).

A good solution will not just be equations but will include some commentary, so everyone can follow your work.

We encourage you to take this opportunity to review any physics you had particular difficulty with. The tutors are here to help you consider the correctness of the physics you are trying to include in your problem.

At the end of the project, please email your problems & solutions to: mcpadden@msu.edu. We will post all of the class's problems as extra resources that you can use for practice and review.