Calculating the strength of a magnetic field in a electromagnet

[balexan]

hi all,

i have just signed up to this site to find some assistance with the above topic.

i am building an electromagnetic propagator to study the effects of varying field strengths on the germination of seeds and the rooting of cuttings.

it has been many years since i last look into such a topic, and i need some help with my calculations.

would someone be kind enough to give me the formula for calculating the field strength produced by an electro magnet (this is my variable). i am only using the simplist of apparatus i.e. an iron core, insulated copper wire, a transformer (this experiment is for 12v only) and sodium lamps.

thanks in advance,

Ben

 

[mfb]

Field strength where? In general, that is a hard problem to analyze in theory.

 

[balexan]

well, the electromagnet will be placed immediately under the seeds and/or cuttings. So the distance between the magnet and the sample will be no more than 15mm
I had hoped that there would be a formula to calculate the strength of the field using the current, length of wire and the number of turns , in addition to the size of core
it is possible that this may not be as easy as i had first thought, but i am keen to run the experiment in this manner as it provides the ability to alter the field strength over a number of different experiments run at the same time
Thanks

 

[mfb]

This thread might be interesting, together with some formulas for electromagnets with a core.

 

[sophiecentaur]

I had a thought that you could probably use the formula for the field inside a long solenoid - if you used a large area solenoid below and above the seed tray. The field would hardly be different from what you calculate if the gap is not great compared with the diameter of the coils. There may be a problem with the lighting, though.
Of course, if you just use a large coil underneath, do a calculation based on the simple solenoid, you would be near the right answer. You could then actually measure the field with a Hall Probe to calibrate the system against the current you are using.