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Physics 20: eLab Activity

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Electromagnetic Induction

Background:

Electric current can be generated in a coil of conducting wire if a magnet is moved through the coil. This fact makes large-scale generation of electric current possible.

In this lab, you will investigate how current is generated with a magnet and wire.

The Questions:

How is electric current generated with a coil of wire and a magnet? What is the relationship between the speed at which a wire passes through a magnetic field and the voltage that is produced?

Variables:

This experiment involves these variables: voltage, speed at which a magnet is moved in a coil of wire, number of wire coils. Identify and state the manipulated, responding, and controlled variables in this investigation.

Materials:

  • voltage sensor and alligator clips
  • USB link
  • RLC circuit board (non-insulated coil of wire can be substituted)
  • long, preferably cylindrical magnet that will fit through the coil of wire
  • lab stands, support rods and clamps
  • paper for making tubes
  • small square of foam about 2 cm thick

Procedure:

Step 1:

Plug the voltage sensor into the USB link.

Step 2:

Attach the RLC circuit board to the lab stand(s) so that it is oriented horizontally about 30 cm above the lab counter. Plug the leads of the voltage sensor into connections on each side of the wire coil on the RLC board. On the lab counter beneath the wire coil, place the square of foam. The square of foam will prevent damage to the lab bench and magnet when it drops through the coil. The apparatus should look something like this:

Step 3:

Configure DataStudio to display a graph of voltage vs. time. Your graph display should be similar to the following:

Step 4:

You are now going to drop the magnet through the coil. Hold the magnet vertically right above the opening of the wire coil. Click START to begin recording data, then drop the magnet through the coil. Make sure the magnet is caught or strikes the foam so as not to damage the lab counter. Click STOP to end data recording. Scale the data on the graph to highlight the area that shows the spike of voltage that occurred when the magnet went through the coil.

*Note - magnets and computer media do not mix! Keep all magnets away from computer media.

Step 5:

Select the voltage data in your graph. Use the "smart cursor" in the DataStudio software to pinpoint the peak voltage produced when the magnet went through the coil (this may be a positive or negative value - it does not matter). Record this voltage value.

Step 6:

Repeat steps 4 and 5 several times, each time dropping the magnet through at a higher speed. Make sure you drop the same end through first every time. The different speeds can be accomplished by dropping the magnet from greater and greater heights. Construct a paper tube that the magnet will fit through. The paper tube can be cut to different lengths (the longer the magnet drops through the tube, the faster it will be travelling when it reaches the coil), this paper tube will guide the magnet through the coil.

Make note of the peak voltages for all your trials.

Analyzing and Interpreting:

1. Why is voltage produced when the magnet passes through the coil?
2. What was the peak voltage produced? What was the relationship between the speed of the magnet and the voltage produced?

Forming Conclusions:

3. Write answers to the following questions:
  • How is electric current generated with a coil of wire and a magnet?
  • What is the relationship between the speed at which a wire passes through a magnetic field and the voltage that is produced?

Extending:

4. Design and conduct experiments to find answers to the following questions:
  • Will a coil generate voltage if a magnet is held inside the coil without moving?
  • How does the strength of the magnet affect the amount of voltage generated?
  • Is the voltage generated any different if the magnet is dropped through with a different pole (North or South) leading the way through the coil?
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