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    For my Advanced Higher Physics investigation I will be doing a series of experiments involving inductors.
    I want to include a section in my investigation about back emf, and I want to be able to calculate it.
    The formula I have is that

    back emf = -inductace x (dI/dt)

    Just wondering how I should go about calculating the inductance of my home made inductor?
    I have found several online "inductance calculators" which claim to do this but I am dubious about these and would rather do it myself if possible.

    The wikipedia page on inductance states that

    L= Nphi / current


    Could I potentially do something like measure the magnetic field with a hall probe and relate this to magnetic flux by knowing the area that I measured it over?

    Or maybe put a voltmeter across an inductor in a circuit, switch on/off the current and see how the back emf affects this somehow?

    Any help will be much appreciated, I'm getting pretty desperate with this investigation.


    you could put the inductor in series with a switch, d.c. power supply and resistor.

    Look at the p.d. across the resistor when the switch is closed, preferably with a storage oscilloscope or data logger.

    The inductance can be worked out from the slope. E = - L dI/dt where E at the start will be equal and opposite to the supply voltage.

    You could also use an a.c. power supply and measure the impedance of a circuit with your inductor and a resistor. From this you can work out the inductance.

    You could put it in a circuit with a capacitor and find the resonant frequency from which the inductance can be calculated.

    This is all pretty standard stuff which you should find in a good textbook.
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Updated: January 20, 2010

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