(a) increases when they are brought nearer.
(d) is the same as M21 of coil 2 with respect to coil 1.
The mutual inductance M12 of coil 1 with respect to coil 2 (a) increases when they are brought nearer. (b) depends on the current passing through the coils. (c) increases when one of them is rotated about an axis. (d) is the same as M21 of coil 2 with respect to coil 1.
The mutual inductance M12 of coil 1 with respect to coil 2 (a) increases when they are brought nearer. (b) depends on the current passing through the coils. (c) increases when one of them is rotated about an axis. (d) is the same as M21 of coil 2 with respect to coil 1.