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Question
A long solenoid is fabricated by closely winding a wire of radius 0.5 mm over a cylindrical nonmagnetic frame so that the successive turns nearly touch each other. What would be the magnetic field B at the centre of the solenoid if it carries a current of 5 A?
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Solution
Given:
Radius of the wire, r = 0.5 mm
Width of each turn, = diameter of the wire, 2r = 1 mm = 1 × 10−3 m
∴ Total number of turns in 1 m solenoid
`n = 1/(1 xx 10^-3 ) = 10^3`
Magnitute of current , i = 5 A
Using B = `mu _0 ni , ` We get
`B = 4 pi xx 10^-7 xx 10^3 xx 5`
`B = 2 pi xx 10^-3` T
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