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B Moving Magnet Along a Conductor

  1. May 24, 2016 #1
    Hi, I have a question regarding electricity.

    Suppose I have a conducting wire secured to a table so it's completely stationary. Suppose I attach a resister of some small amount of resistance, perhaps a light bulb.

    Then I take a magnet and slowly move the magnet near the conductor so that a current is induced. Let us call this trial 1.

    Then, I swing the magnet again along the same exact path as in trial 1, except this time, I have moved the magnet 10 times as fast as in trial 1.

    Suppose that in both trial 1 and trial 2, I have cut the same exact lines of magnetic flux at the same points in the same sequence, and the only difference between the two trials is the speed along the trajectory.

    My question is in regard to voltage, current, and power:

    Does the speed change any of the electrical features?
    Does the faster swing induce a stronger voltage?
    If so, then since resistance stays the same, the current must have also increased with voltage.
    If time decreased, then power must have increased (according to newton's law energy/time = power), right?
    If I am wrong in that speed of the swing does not change the voltage nor the current, then does power still increase since time still decreased from trial 1 to trial 2?

    Are these beliefs correct?
  2. jcsd
  3. May 24, 2016 #2


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    welcome to PF

    sounds like an excellent and safe experiment you can do at home and then report back with your findings
    you should be able to answer all your questions

    one clue

    generated power can only increase IF voltage and or current is increased
    Don't use Newton. just use plain P = V x I

    do your experiments and tell us how you got on

  4. May 24, 2016 #3


    Staff: Mentor

    Are you familiar with Faraday's law?
  5. May 24, 2016 #4


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    You can answer your last question by thinking about the conservation of energy.
  6. May 24, 2016 #5
    I don't have a magnet. I don't have wire. I don't have any type of electrical metering device. I kind of was hoping to understand this without reinventing the wheel at the moment lol.
  7. May 24, 2016 #6
    No Sir. I will look into it.
  8. May 24, 2016 #7
    I was hoping to get some feedback on each of the questions though lol :)
  9. May 24, 2016 #8
    Okay, just looked into it. That math seems way beyond my level at this time.

    Was just wondering if voltage, current or both change in a conductor when you increase the speed of a magnetic passing by.

    Just was asking because households have 60 hz voltage and jet aircraft have 400 hz voltage and I was just wondering what the reason for different frequency was.

    Don't know about double integrals and don't own a multimeter at this time. Was just hoping for some insight. Thanks.
  10. May 24, 2016 #9


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    seriously ....
    those are not excuses ... magnets are cheap $00.00 to a couple of bucks, wire likewise, a light globe likewise
    multimeters are available for around $10 if you shop around

    we are here to help people learn, not spoonfeed them the answers
    you have posted an ideal experiment setup, how about making just a little effort on your own :smile:

  11. May 24, 2016 #10
    I do make a lot of effort. I guess time is just not on my side at the moment. I didn't realize asking a legitimate question equates to requesting to be spoonfed. I must be a really lazy and ungrateful person. Anyway, thank you for welcoming me to this forum.
  12. May 24, 2016 #11

    I found the answer to my question:

    The amount of voltage is determined by 3 factors. Strength of magnet, length of the conductor cutting the flux, and the velocity that the magnet is moving through the flux.

    It is determined by E = B l v = (magnetic strength)(length of moving conductor)(velocity of the conductor).

    As I mentioned, I am mainly interested in the velocity factor.

    Unfortunately, I did not learn this through my own experimentation, but through experimentation of many before me via youtube video.
  13. May 25, 2016 #12


    Staff: Mentor

    Ok, there will be a limit to what I can say, but basically Faradays law says that the voltage induced in a loop is proportional to the rate of change of the magnetic flux through the loop.

    So if you use the same magnet then you will have the same total change in flux. If you move it faster then what will happen to the rate of change? And then applying what you now know about Faradays law what will happen to the voltage?
  14. May 26, 2016 #13
    Rate of change will increase. So voltage will increase?
  15. May 26, 2016 #14


    Staff: Mentor

    Yes, exactly
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