In designing the instrument required to calculate the coil, the magnetic field inside which would be near the middle is 4 * 10 ^ 4 grade A / m. The winding is made of wire having a diameter of 0.225 mm, which maintains the current strength of not more than 1.5 A. From a minimum number of layers will be composed of the solenoid coil when wound coils close to each other?

Detailed solution shorthand terms, formulas and laws used in the decision, the withdrawal of the calculation formula and the response.
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