Electromagnetism — Experiments With a Bicycle Dynamo
This experiment shows how the output of a bicycle dynamo can be displayed using a PC–based oscilloscope. It assumes a basic knowledge of electromagnetic induction.
Contents:
Equipment required
Any bicycle dynamo should be suitable for these experiments. We used a bicycle dynamo with a pulley wheel, handle and bulb mounted on a demonstration stand. This was purchased from Griffin Education (part number XKE-650-J).
Experiment set up
The experiment was set up as shown in the photograph below.
Experiment results
To test the set up, the handle on pulley was given a single turn. PicoScope oscilloscope software was set to single–shot trigger to capture the results. Pre–trigger (20%) was used to show signals before and after the trigger event. The PicoScope screen shot shows the results:
Questions
- How long did the dynamo keep turning?
- What was the maximum voltage it produced?
- What happened to the speed of rotation of the dynamo whilst it was turning?
- How was the voltage related to the the speed of rotation of the dynamo. Use your knowledge of electromagnetic induction to explain this.
- The dynamo is connected via pulley and handle which produces several turns of the dynamo for one turn of the handle. Approximately how many times did the dynamo rotate (assume one cycle per rotation) for one rotation of the pulley handle?
Further experiments
Using PicoScope meter functions, the relationship between speed of rotation and output voltage can clearly be seen. We experimented using an AC Voltmeter and Frequency meter (see screenshot). If you want to investigate this further, try using PicoLog data logging software to plot voltage against frequency.
When we disconnected the bulb from the circuit, the signal increased in amplitude and changed shape (see below). Explain why this happens.
