A uniform current `I` is flowing in a long wire of radius `R`. If the current is uniformly distributed across the cross-sectional area of the wire, then

Options

A. magnetic field inside the cylinder increases linearly from zero at the centre
B. magnetic field will be maximum at a point on its axis
C. magnetic field will be maximum at a point on its surface
D. magnetic field is minimum at a point on its surface

Answer

a, c

Explanation

Magnetic field intensity due to this system at a point at a distance from its centre is given as follows:
` x lt R : B = (mu_(0) I x)/(2 pi R^(2))`
` x gt R : B = (mu_(0)i)/(2 pi x)`
Hence magnetic field is zero at x = 0 and option (a) is correct.
Magnetic field is increasing linearly from the centre up to the surface and then further, it decreases inversely proportional to the distance, hence it attains a maximum field at the surface. Thus, option (c) is also correct.