Electromagnetic Induction Demonstration
This material is replicated on a number of sites
as part of the
SERC Pedagogic Service Project
Initial Publication Date: April 27, 2010
Summary
The level of explanation for the demonstration can vary from a very qualitative discussion of magnetic fields to a quantitative discussion of transformer theory.
CollapseLearning Goals
At the end of this activity the students will understand there is a relationship between the electric and magnetic fields. Specifically, they will verify that a magnetic field is created in a current carrying coil of wire and a changing magnetic field can induce a current in another coil of wire.
More advanced students will learn the relationship between the induced current and the spacing of the coils or the number of turns in each coil.
More advanced students will learn the relationship between the induced current and the spacing of the coils or the number of turns in each coil.
Context for Use
Conceptual or introductory high school class:
Materials:
1 small radio or ipod
1 small external speaker (Radio Shack Model: 277-1008 )
1 mini stereo cable (Radio Shack Model: PH62125 )
1 mini stereo cable cut in half with coils of magnet wire on each end
Materials:
1 small radio or ipod
1 small external speaker (Radio Shack Model: 277-1008 )
1 mini stereo cable (Radio Shack Model: PH62125 )
1 mini stereo cable cut in half with coils of magnet wire on each end
Description and Teaching Materials
The demonstration is set up by:
1. Turning on the radio and the speaker and connecting the cable between them
2. Removing the cable and replacing each end with the modified cable (coils of wire on each end)
3. Slowly bring the coils close together until the music is heard.
The students will be amazed and ready for an explanation. Several concepts can be discussed:
1. A current carrying coil of wire creates a magnetic field through it. Equations can be discussed if desired.
2. A changing magnetic field induces a current in a coil of wire as stated by Faraday's law of induction
3. A basic transformer is two coils of wire that can transfer electrical energy without touching.
For a more detailed discussion, the spacing of the coils can be changed, a piece of iron can be place through both coils, or coils with varying numbers of turns can be used.
1. Turning on the radio and the speaker and connecting the cable between them
2. Removing the cable and replacing each end with the modified cable (coils of wire on each end)
3. Slowly bring the coils close together until the music is heard.
The students will be amazed and ready for an explanation. Several concepts can be discussed:
1. A current carrying coil of wire creates a magnetic field through it. Equations can be discussed if desired.
2. A changing magnetic field induces a current in a coil of wire as stated by Faraday's law of induction
3. A basic transformer is two coils of wire that can transfer electrical energy without touching.
For a more detailed discussion, the spacing of the coils can be changed, a piece of iron can be place through both coils, or coils with varying numbers of turns can be used.
Teaching Notes and Tips
The coils can be made by stripping the ends of a long piece of magnet wire (about 20 gauge for strength(, forming a coil with about 5 loops and soldering the ends to the two leads of the mini-stereo cable.
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Assessment
White boards can be used to have students sketch the coils and fields after the demonstration and before the discussion.
References and Resources
http://faraday.physics.uiowa.edu/em/5k10.51.htm
