Science Buddies: "Ask an Expert"

Hi, for school i am required to make an ac generator that can turn on a 1.3Ω light bulb. This will be generated by dropping a 100g mass down a distance of 1.5m.
What we have done so far is wrapped copper wire (0.4mm) around a toilet paper roll. Through this we have put through a skewer which has two magnets (rare earth magnets) attached on either side (of the skewer), spaced apart so they are not touching. The set up is made of lego and the toilet paper rests at a height, allowing the skewer and magnets to pass through without hitting the walls of the roll. The skewer is sitting flat through two lego pieces with holes. At the end of the skewer, rope is wrapped around. The rope is tied to two 50g masses. The ends of the copper wire have been sanded slightly and attached to the light bulb.
When the masses are dropped and the magnets spin, the light does not turn on. We do not know what to change in order to make this work and were hoping you could help. Thanks,

Hi bront3,

I assume your setup looks similar to http://amasci.com/amateur/coilgen.html.

Here are a few things I can think of that might go wrong:

• The wire ends don't connect properly to the light bulb
  • If you soldered the wires to the light bulb, the solder joints could have broken or didn't fully connect
    If you wrapped the wires around the light bulb terminals, try sanding the wires more and re-connecting them.
  The light bulb burnt out.
  • If the resistance across the light bulb terminals (without anything else connected) is very large (> 1 MegaOhm), then the light bulb burnt out, and you will need to replace it.
  Your setup works, but is just really dim. Some possible suggestions:
  • Increase the number of coils to increase the current/brightness
    Spin the setup faster
    Test your setup in the dark to check if the light is just dim.

If those suggestions don't work, let us know. A photo of the setup may help us provide more suggestions.

Best,
Charles