A long solenoid is fabricated by closely winding a wire of radius 0.5 mm over a cylindrical non-magnetic frame so that the successive turns nearly touch each other. What would be the magnetic field B at the center of the solenoid if it carries a current of 5A?

Given:


Radius of cylinder(r) = 0.5 mm = 5 x 10-4 m


Current(i) = 5 A


Formula used:


Magnetic field inside a long solenoid B = μ0ni,


where


μ0 = magnetic permeability of vacuum = 4π x 10-7 T m A-1, n = number of turns per unit length, i = current carried by the wire


Now, width of each turn = diameter of the wire = (0.5 x 2) mm = 1 mm = 10-3 m.


Hence, number of turns per unit length(n) (per m) =103 = 1000


Therefore, substituting the values:


B (magnetic field at the center) = 4π x 10-7 x 1000 x 5 T


= 6.28 x 10-3 T (Ans)


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