Coil C carries a steady current. A second coil is placed in close proximity to coil C as shown in figures given below. Arrange the following options in the correct order of decreasing mutual inductances for the pair of coils.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, C, D, B
The mutual inductance of two coils measures how much of the flux of coil C passes through the second coil. It is largest for coaxial coils in parallel planes close together, and it falls as this flux linkage falls.
(A) The two coils are coaxial, in parallel planes and close together, so almost all the flux of C passes through the second coil: M is the largest.
(C) The coils are again coaxial and parallel, but the second coil is smaller, so it catches only part of the flux of C: M is smaller than in (A).
(D) The second coil lies in the same plane as C, beside it, so only the weak return flux outside C passes through it: M is small.
(B) The plane of the second coil is perpendicular to the plane of C, so the field lines of C run along the second coil’s plane and do not pass through it: M is practically zero.
So the decreasing order of mutual inductance is A, C, D, B.
NCERT (2026-27):
Mutual Inductance – “… It is also important to know that the mutual inductance of a pair of coils, solenoids, etc., depends on their separation as well as their relative orientation.”