1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Piece of metal being carried through an inductor

  1. Apr 12, 2012 #1
    Hi, I have some questions about a piece of metal traveling through an inductor with DC current flowing through it. Imagine a solenoid of sorts with a hole in the middle that a piece of neutrally charged metal travels through, sort of like a coil gun.

    Let's say the inductor has no current running through it, then we turn it on. It will take time to get up near it's peak magnetic field output, correct? I know the current takes time to get going, and the magnetic field is proportional to the current. And if the piece of metal is attracted to the solenoid, then the piece of metal will travel through the solenoid. Will the piece of metal being attracted by and traveling through the solenoid disrupt the current/magnetic field of the solenoid? As in, will the solenoid take longer to "get going" if it is attracting a piece of neutral metal?

    My last question is, will the piece of metal be attracted to both sides of the solenoid (instead of attracted by one and repelled by the other) even though the magnetic field goes straight through the solenoid? I'm pretty sure the answer is yes but I'm just making sure.

  2. jcsd
  3. Apr 14, 2012 #2
    I would model this using the free electrons moving into the B field of the solenoid.
    What direction are the free electrons moving in the B field. And then use the Lorentz force to see which way the electrons will move in the conductor. Will there be an induced current in the conductor and if so what direction is it? F=q(vxB)
    Good questions you bring up.
  4. Apr 14, 2012 #3
    Thanks, but I still have a lot of difficulties. Such as, the force acting on the electrons is in the same direction as the magnetic field in the solenoid.
  5. Apr 16, 2012 #4


    User Avatar

    Staff: Mentor

    Copper and aluminium (non-magnetic) will behave differently to steel and nickel.
    If you quickly slide the iron core into an energized solenoid, the core can travel through and partly emerge from the far end, then get pulled back in, then bounce back and forth until it settles.

    Iron dropped into the solenoid just as it's being energized will increase the inductance, causing the coil's current to rise more slowly. :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook