course_planning:184_projects:f18_project_13 [Projects & Practices in Physics]

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===== Project 13 =====
==== Project 13A: Poop in a Loop ====

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Dramatic events have occurred all over the world as the stormclouds and alien spacecraft have been repelled by what has been described as reverse Hawkion beams. The breakthrough came when it was realized that you must cross the beams in order to disrupt the alien technology. In Lakeview, life has gotten back to relative normality but the town continues to use the magnetic field in order to keep any remaining boar tigers away. There has been the added bonus that there has been a drastic reduction in car accidents due to the populace being afraid that the magnetic field will destroy their engines. However, tranquility is unsettled when the government agency P.E.R.L. comes to town in order to try and capture a live adult EM Boar Tiger. S.P.A.R.T.A.N force has been tasked with acting as a local guide, as P.E.R.L head into the surrounding forest to complete their investigation. Once deep in the forest, your party is ambushed by boar tigers and several of the team are captured and taken away. The remaining members of the team try to follow the tracks of the Boar Tigers but this becomes impossible after a time. However, you remember hearing from Dr. O'Tallest who did research on the boar tigers that their excrement has a very high percentage of nickel in it (it was the colorful poop that kept on being found all over town). You indicate to the group that you think you can McGyver a metal detector together to track your kidnapped colleagues. You have access to a whole bunch of 12 gauge copper wire, an alternating current power supply that can produce a maximum current of 2 A and has a frequency of 60 Hz, and a voltmeter that will measure an alternating voltage. If the voltmeter measures a voltage bigger than 50 mV, it will sound an alarm. You want to design your metal detector so that if there is not a metal nearby, the voltmeter will be below the threshold; however, if there is a metal nearby, then the measured voltage on the voltmeter will be above the threshold and set off the alarm. 

<WRAP info>
=== Learning Goals ===
  * Explain how a metal detector works (be able to explain what happens when a metal is present and not present)
  * On a microscopic level, explain what happens to the metal pieces when placed in a magnetic field.
  * Make a current vs time graph for the alternating current and for the induced current. Explain any similarities and/or differences in the graphs.
  * Use the right hand rule to check the direction of the induced current.
</WRAP>

==== Project 13B: 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>