A long cylindrical wire carries a steady current which is uniformly distributed across its cross section. Which of the following is true?

Options

A. Magnetic field is zero at the centre.
B. Electric field is zero at the centre.
C. Electric field just outside the cylinder is zero.
D. Magnetic field just outside the cylinder is zero.

Answer

a, c

Explanation

Magnetic field intensity due to this system at a point distance x from its centre is given as follows:
` x lt R : B = (mu_(0)ix)/(2 pi R^(2))`
` x gt R : B = (mu_(0)i)/(2 pi x)`
Hence magnetic field is zero at a point on its axis and it is non-zero just outside the cylinder.
Current is flowing in the cylindrical conductor, hence electric field exists inside it along the length, which is applied from some external source like battery. But as a whole, the cylindrical wire is neutral so it will not create any electric field in its surrounding. Options (a) and (c) are correct.