Function Generator Question

Discussion in 'The Projects Forum' started by sspil, Feb 25, 2010.

  1. sspil

    Thread Starter New Member

    Feb 12, 2010
    11
    0
    I am setting up a mutual induction lab for my physics class. I thought I had everything hooked up correctly, but I'm getting such tiny output on the outer coil. Here is the lab I am using as my guideline:

    http://physics.ua.edu/lab10x/ph106/PDF/Mutual_EMF_LAB.pdf

    When I measure the output of the function generator, I am getting about 7.4 VAC. When I attach it to the inner coil, the voltage drops to the millivolt range when I measure it across the inputs. Maybe I am not understanding the function generator properly, but I don't understand why I'm getting such a huge drop in voltage. Is it that the function generator doesn't have the power to drive the signal through the coil? Should I be connecting the neg. side of the function generator and the coil to ground instead of each other?
     
    Last edited: Feb 25, 2010
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    You will need an amplifier. Most function generators are pretty high impedance outputs, and the coil experiment is going to be very low impedance.

    What make and model of function generator do you have, or is it a home brewed job?

    Amplifiers are pretty easy to build, but you will also need a power supply capable of providing the current.

    If you have an old boom box you don't mind risking that has audio in/audio out (and assuming the frequency is audio) you could use that.

    While I have never built it, I think this design of amplifier would work.

    http://forum.allaboutcircuits.com/album.php?albumid=26&pictureid=411

    [​IMG]

    You may want to go conservative and use a more established design, which I am sure one of our other members will provide.
     
  3. sspil

    Thread Starter New Member

    Feb 12, 2010
    11
    0
    Thanks for your help! I suspected an impedance mismatch but wasn't sure. I don't have the make and model of the function generator here with me, but it is a purchased unit, not home made. There isn't an amplifier on the unit itself like some of the more expensive units have.

    I don't think I'll have time to procure parts and teach myself to build the amplifier I need before I need to run the lab. I'll have to think of something else to have them do. I'm limited with what they have on hand at the school. There must be or must have been the proper equipment to run the coil lab at one time in the store room because they have most of the parts. Maybe the amplifier is there and I just need to hunt it down. I'm finding bits and pieces of standard labs, but parts are missing or damaged. Sadly anyone who had knowledge about the equipment in the store room is long gone.
     
    Last edited: Feb 25, 2010
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    Keep the audio amp in a boom box in mind. What was used before may not jump out at you. A PA amp would probably work well too.
     
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