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# Re: [femm] high schoool science project

- To: <femm@egroups.com>
- Subject: Re: [femm] high schoool science project
- From: "ernestfreeman" <ernestfreeman@email.msn.com>
- Date: Sat, 8 Apr 2000 09:09:03 +0100
- Organization:
- References: <8cmkbm+2c0o@eGroups.com>

    Greetings jtheobald.

    1. It would be helpful to know your academic level, what exams have you
    passed in science? I can then pitch my replies accordingly.

    2. It is extremely difficult to calculate magnetic fields when you have
    iron present. You really need a computer aided design (CAD) package. Try
    this website...

    http://members.aol.com/gmagnetics/download.htm

    This will not be easy for you, but will show you what is possible. Also
    look at the listed companies, their websites will give you a good idea of
    the state of the art.

    3. If the coil is in air, with no iron present, then you can calculate
    the field on the axis. This is very easily done for a single circular coil,
    see A-level physics texts. Off-axis is very tricky using closed form
    algebraic expressions. For a solenoid, divide it up into a large number of
    thin circular coils, then add them separate fields together. I use a spread
    sheet for that sort of tedious calculation.

    4. To calculate forces, you really need fields. Then you would apply
    Maxwell stress formulae. Again, you need a CAD package.

    There is another technique based on rate of change of inductance. Measure
    the inductance with the iron piece at several distances along the axis,
    keeping the dc current constant. Plot inductance against distance. Then
    the force is given by.....

    Force = 0.5*(dc current)^2*(rate of change of inductance with distance) in
    Newtons

    5. To a first approximation, the power required will be independent of
    the number of turns, for a given force. Also, do note that the field is
    proportional to (turns*current).

    6. The Institution of Electrical Engineers, (IEE), London, has links to
    schools. That means that your school could have a direct link to the sort of
    expertise you are tapping with this enquiry.

    7. I work at Imperial College. It runs the Pimlico Project, to take
    science into schools. If your school is in or near london, that might be
    worth noting.

    8. Please show this to your teacher.

    9. As an aside, I enjoyed your joke spelling, but I am sure that for
    serious correspondence you would run everything you type through a spelling
    checker.

    Good luck, E.M.Freeman

    Professor E.M.Freeman, FREng, FIEE, FRSA, PhD,
    Professor of Applied Electromagnetics,
    Electrical and Electronic Engineering Department,
    Imperial College of Science Technology and Medicine,
    Exhibition Road, London, SW7 2BT, UK.
    phone:0171-594-6166, fax 0171-594-6167, ernestfreeman@msn.com

- References:
  - high schoool science project
    - From: jtheobald@cannondesign.com

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