Find the electric current, or "I," flowing through the magnetic coil. Refer to the design specifications for your magnetic circuit or system and look for the average or anticipate current flow. Current will be in units of amperes.
How to Calculate the Strengths of Magnets
A more common name for strength of a magnet is magnetic field strength. The magnetic field strength depends on the magnetic circuit. A magnetic circuit works similarly to an electrical circuit. For example, an electric circuit obeys Ohms law, which states that voltage is equal to the current time the resistance. In a magnetic circuit, the magnetomotive force is equal to the magnetic flux multiplied by the reluctance. The magnetomotive force is proportional to magnetic field strength, magnetic flux is analogous to current and reluctance is analogous to resistance.
Things You'll Need
 Design specifications for your magnetic circuit or system
 Calculator
Instructions


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Find the number of turns of wire in the coil, or "N". Refer to design specifications.


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Find the length of the magnetic circuit, or "L". The magnetic circuit is the length of the iron core. However, if an air gap exists, as with a "C" shaped magnetic coil, the magnetic circuit will be the length of the core plus the length of the air gap. Refer to design specifications of the coil. L is in units of centimeters.

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Calculate the magnetic field strength for the coil using the formula: S = (I x N)/L where S stands for magnetic field strength. As an example, if I is 2 amperes, N is 15,000 turns and L is 18 centimeters, S = (2 x 15,000)/18 = 1,667 amperesturns per centimeter.

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References
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