A long solenoid of 50 cm length having 100 turns
carries a current of 2.5 A. The magnetic field at
the centre of the solenoid is :
(``µ_0``
=4π×``10^{-7}`` T m A-1)
(1) 6.28×``10^{-4}`` T
(2) 3.14×``10^{-4}`` T
(3) 6.28×``10^{-5}`` T
(4) 3.14×``10^{-5}`` T