A solenoid 4 cm in diameter and 20 cm in length has 250 turns and carries a current of 15A. Calculate the flux through the surface of a disc of 10 cm radius that is positioned perpendicular to and centered on the axis of the solenoid

R = radius of solenoid = 2 cm L = 20 cm,    turns = N = 250 turns per unit length = n = 1,250 turns/meter current i = 15 A Magnetic field through the solenoid = μ₀ n i = 4π * 10⁻⁷ * 1,250 * 15  units          B = 2.356 * 10⁻² H The magnetic field outside the turns of the solenoid is zero, ie., it exists only in the area of π r². Flux = B * πr² = 0.0185  Volt-sec