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?

Explanation

Given r= -0.5 mm
so, width of each turn
`=1mm = 1xx10^(-3) m`
:. Number of turns, `n = (1)/(1xx1-0^(-3)) = 10^3`
`i=5A`
Since `B =mu_oni`
`=4pi xx10^(-7)xx10^3xx5`
`=2muxx10^(-3) T.`