184_projects:s20_project_13 [Projects & Practices in Physics]

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===== Project 13 =====

==== Project 13A: Clean Source of Energy or Hidden Stash of Jellybeans??? ====

{{ 184_notes:13a_picture.png?700 |Alternative Energy Source}}

The people of Lakeview are starting to get used to living life in the magnetic field, now that it seems to be doing a pretty good job keeping EM-boar tigers from entering into the center of town and causing mayhem. Local alternative energy scientist Alysson Watersa has even installed a source of clean energy that is made possible by the magnetic field. This could be incredibly useful if anything happens to the powerplant. She has constructed a water mill with her bare hands and situated it into the side of the cliff, conveniently below a waterfall so that the motion of the water turns the mill at a frequency of $15 \text{ rpm}$. Dr. Watersa also fixed a board along the axle of the mill, and she has laid a loop of 12-Gauge copper wire (with a radius of $1 \text{ m}$) on the board. One end of the loop becomes a wire that comes out the side of the board and is grounded into the cliff. The other end of the loop becomes a wire that runs out the other side of the mill, all the way back to Lakeview. As the mill turns, so does the loop, causing a current to exist in the wire, which can be used as a small convenience for the good people of Lakeview.

Unfortunately, local superstitious person Manny Hallabero is causing a ruckus again, this time about the new energy source. He claims that it's all hocus pocus, and Dr. Watersa is just using the water mill as a ploy to hide her stash of jellybeans in the face of the cliff in order to avoid sharing. Clearly deluded, he won't listen to Dr. Watersa for even a second, so it's up to you to explain to Manny how the water mill works and why it produces the current that it does. It may be helpful for Manny to see a diagram of the mill and a graph of the current produced as his special type of crazy his often open to representational data. Be as detailed as possible, as Manny can be very stubborn about changing his mind. Dr. Watersa's blueprints, shown below, may be helpful.

{{ 184_notes:13a_representation.png?600 |Diagram}}

<WRAP info>
=== Learning Goals ===
  * Calculate the induced current from a changing magnetic flux
  * Use the right hand rule to determine the direction of the induced current
  * Explain why induced current is different from the current in a circuit (in other words, what does it mean for a current to be "induced"?)
  * Explain why there is a negative sign in Faraday's Law
</WRAP>



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

{{ 183_projects:rainbow.jpg?300 }}

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>