Connections in Electricity and MagnetismFirst discovered by Michael Faraday, electromagnetic induction is the process of using magnetic fields to produce voltage, and in a complete circuit, a current. He started, at first using different combinations of wires and magnetic, but it wasn't until he tried moving the wires that he created a current. It turns out that electromagnetic induction is created by just that – moving of a conducting material through a magnetic field (or the moving of a magnetic field past a conductor). Electric guitars make use of Faraday's discovery. Pick-up coils, consisting of a small magnet wound with wire, created an interaction with a magnetic string or wire, which in turn creates a current in the coil. This current can be transmitted to a speaker and converted to sound by a reciprocal process. While Faraday discovered the science, most historians give credit to Leo Fender, who in the 1940s created the electric guitar. In this lab you will learn how a pick-up coil works and use a home-made pick-up to play the \'physics guitar.\'
Materials Guitar pick-up stick Alligator to (mono) audio connector Mini amplifier Guitar string board A word of caution: the guitar string board is not a guitar. The board is just a way to mount strings of different modes of vibration. It cannot be tuned like a guitar. If you try, you will break the strings. Please do not!
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Procedure 1. Attach two wires on the electric "pick-up stick" to the speaker-amplifier using the alligator to mono audio connector. 2. Tum the amplifier to the on position and turn the volume knob to near maximum. 3. Slide the "pick-up stick" magnet under one of the strings and pluck the string (making sure the magnet does not touch the string). 4. Move the magnet in and out from under the string while it is vibrating and note what happens. 5. Draw the magnetic field lines of the magnet on the pick-up stick. 6. What is the purpose of the magnet inside the coil on the pick-up stick (i.e. what function does it serve? Revised from Overhiser and Donev, 2006, Cornel University, by David Sederberg, Purdue University Science Express, 2018 6 7. The magnet in the center of the coil is not moving through the coil. Explain how the wire coil is able to generate a current. 8. Why wont nylon strings work on an electric guitar?
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Activity 5 Talking back to the speaker. In this activity you will identify the parts of a common loud speaker and consider how it works relative to the force created by the interactions between magnets and coils of current-carrying wire. Materials Mini amplifier Alligator to mono connector Small loud speaker
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Procedure 1. Study Illustration C to the right and find the components we have discussed to this point: the coil and the magnet. 2. Connect the mini-amplifier to the small speaker using the mono-to-alligator adapter. Very gently tap the loud speaker and observe the effect. 3. Using the same set-up, talk into the loud speaker. 4. Make a list of the sequence of events that results in a current when talk into or tap on the speaker. Revised from Overhiser and Donev, 2006, Cornel University, by David Sederberg, Purdue University Science Express, 2018 7 Activity 6 Making your own speaker and microphone. You will now be able to identify the parts of a common loud speaker and consider how it works relative to the forces created by the interactions between magnets and coils of current-carrying wire.
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