Effect of an electric current on a spiral metal spring

Discussion in 'Physics' started by physicsstudent1, Apr 11, 2011.

  1. physicsstudent1

    Thread Starter New Member

    Apr 11, 2011

    I'd be grateful if anyone can help me with a science project. Here is some information on the project:

    It is suggested that a spiral metal spring will undergo a small contraction if an electric current is passed through it.

    My question is, how would I design an experiment to investigate this effect? (I must include a diagram showing the arrangement of the apparatus and a description of the procedure to be followed)

    Additional information:
    Special attention should be paid to
    -the stiffness of the spring that is to be used,
    -the magnitude of the current to be passed through the spring
    -the method of measuring the contraction of the spring (given that it is likely to be very small).

    Also, are there any difficulties that I might expect to encounter?

    If anyone has any ideas I'd be grateful to know what they are, thank you.

    -Darien (physics student in need of HELP!)
  2. someonesdad

    Senior Member

    Jul 7, 2009
    Sounds like an interesting experiment! Lots of things to think about.

    The first is to outline the mechanisms based on your knowledge of physics as to why the spring might move. Is it an electrical effect? Mechanical? Combination of both? What properties of the spring material might influence it? Does the direction of the current matter? Will it happen with an AC current? If so, is it frequency dependent?

    The actual design of the apparatus to detect the movement will be interesting too. What's a good way to detect the movement? You might want to read up about an optical lever (how about a mechanical lever?). What about videotaping the spring through a magnifier or using a macro lens? Could a sensitive and low-mass LVDT sensor be used? How about capacitively measuring the displacement?

    Remember that the careful experimenter designs an experiment with a null hypothesis and an alternative hypothesis. Then data are gathered and analyzed and one or more conclusions made. Then the experimenter has to decide whether a) the data are consistent with the null hypothesis and thus, it can't be rejected (but this doesn't "prove" it's true!) or b) the null hypothesis has to be rejected.

    Once these concepts are internalized, then your design strategy revolves around finding an efficient way to find out whether the null hypothesis can be rejected. I glibly make it sound easy; however, many professional scientists aren't very well trained on this stuff. You can show them up. :p
  3. Wendy


    Mar 24, 2008
    I've never heard of it, but I won't dismiss it. There are lots of things I've never heard of.

    One thing to consider, that spring is also a coil. It generates a magnetic field, and has inductance.
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    The effect may be complicated by heating. In a coil of some length, that might easily be the most obvious effect. In Fords, at least, the automatic choke was controlled by a coil that changed length with temperature.
  6. physicsstudent1

    Thread Starter New Member

    Apr 11, 2011
    Thank you all for your input. I'm sure it will help.
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Choke coils, and in the old days exhaust heat riser coils were both made of a 'bi-metal 'strip. The same basic principal as a old style house (heating) thermostat.
    Last edited: Apr 13, 2011
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    a 'slinky' might show some twitching, or the like, when you send a surge of juice through it. The steel will certainly help it react to the magnetic field generated. The added resistance of steel versus copper will mean you have to keep the battery connection time very short and let the wire cool between demo's.
  9. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    I'm thinking your movement will be very small, and you should be prepared to measure expansion as well as contraction. My suggestion would be an optical flat.
  10. mcike

    New Member

    Apr 17, 2011
    start to read about Lorentz-force and Ampere's force law. Former, 1Ampere was defined describing the attractive force between two parallel wires carrying an electric current.
    Describing springs might be much more difficult, because forces on windings in the middle of the spring may cancel out. Anyway, this doesn't hold for first and last winding.
    Hope this hints are helpful. :)

  11. physicsstudent1

    Thread Starter New Member

    Apr 11, 2011
    Thanks for the advice! So the scientific principle that this experiment could be based on, could be Ampere's Force Law?

    Thanks again to everyone!
    Last edited: Apr 18, 2011