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If a rod permenant magnet enters a coil at a certain speed and the coil absorb its ki

  1. Jun 17, 2012 #1
    If a permanent magnet rod enters a coil of wires at a certain speed will the permanent magnet slow down? I'm trying to build a generator of some sort. So i need to know is my logic sound. I'll give you scenario.


    The permanent magnet slides into the coil at a speed of 3meters/second. What will the speed of the magnet be after exiting the coil?

    Permanent magnet parameters
    Mass : 2kg
    Strength : 2000Gauss or 0.2Tesla
    Area : 0.008m2

    Wire Coil Parameters
    Turns : 20000
    Resistance : 50 Ohm
    Length of Coil : 3meters

    Thus the energy contain in the magnet moving at 3ms-1 is = 9joules

    E=1/2 mv^2

    So using faradays law, the power generated by the magnet passing thru the coil of wire :

    V= (-N)(BA/t)
    V = voltage
    N = Turns
    B = Flux (in tesla)
    t = Round per second
    A = Surface Area of permanent magnet

    Note : I will reduce the flux strength to 0.1tesla because the coil will be approximately 2mm from the magnet

    V = (-20000)(0.1*0.008*/1)
    V = 16Volts

    Thus the current generated is


    I = 16V / 50ohm
    I = 0.32amps

    Thus power generated is

    Power = VI
    Power = 16V * 0.32amps
    Power = 5.12Watts or joule per second

    Thus the speed of the permanent magnet exiting the coil is

    9joules – 5.12 joules = Kinetic Energy Remaining

    3.88 = (1/2)(2)(v ^2)
    v = √(3.88*2/2)
    v = 1.96ms-1

    Is this logic and calculation correct??
  2. jcsd
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