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Faraday Flashlight/Torch

  1. May 2, 2015 #1
    So I have a very basic question, but I have next to no electrical understanding so can't answer it myself.

    With a Faraday torch you shake a magnet in a coil to create electrical charge. They say the harder you shake the more charge you create, so my question is this... is it the increased number of passes the magnet makes through the coil that would create more charge, or is it the speed of the magnet passing through the coil that creates more charge?
  2. jcsd
  3. May 2, 2015 #2

    Simon Bridge

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    Its a bit of both - but basically (mostly) each pass of the magnet moves a set amount of charge from one place to another. It's like pumping water.
    Note: no charge is created or destroyed in this process.
  4. May 3, 2015 #3
    Thanks for the reply.

    So do you think a single pass through a 1m long coil could produce the same amount as multiple passes through a 0.1m long coil?
  5. May 3, 2015 #4


    Staff: Mentor

    The number of turns, not the length is the key parameter. There are complexities such as leakage flux, but in a rough sense yes. The number of passes times the number of turns should be roughly proportional to the amount of charge.
  6. May 5, 2015 #5

    Simon Bridge

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    You can imagine if you just inverted the coil+magnet, allowing the magnet to fall - then the setup converts a proportion of the gravitational potential energy into electrical energy stored in a battery. Twice the coil length (all else i.e. the turn density remaining equal) gets you twice the GPE ans so twice the electrical energy.
    This would be the same if you just shook it horizontally - bearing in mind you'll also need twice the effort.
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