Question

consider a series of four long concentric cylinders, each carrying the uniform current I in alternating directions into and out of the page, as shown in the figure. For this problem, each cylinder is considered to be infinitely thin! let r denote the radial distance from the center of the cylinders.

the magnetic field is zero

Consider a series of four long concentric cylinders, each -1 into page 2 carying the uniform current Iin alternating directions into and out of the page, as shown in the figure. For this problem, each cylinder is considered to be infinitely thin! Let r denote the radial distance from the center of the cylinders. The magnetic field is zero (A) only for r<a (C) only for r<a and b < r < c and r > d I out of page^ ) only for a <r< (E) only for r>d

Answer 1

Therefore, option(C) is correct.   

Using Ampere's circuital law, B^vector. dl^vector = mu. I_enclosed B = magnetic filed case 1 r < I. therefore I_enclosed = zero therefore B = 0 case 2 a < r < b Net I_enclosed will be present due to the presence of wrrent on the wire with radius 'a' therefore B notequalto 0 case 3 b < r < c. net I_enclosed = zero therefore B = 0 case 4 c < r < d. i_enclosed will be present in clock wise direction therefore B notequalto 0. Case 5 r > d. Net I_enclosed = 0 therefore B = 0 therefore option (C) is correct.