Question

Two coils of self-inductance L 1 and L 2 are connected in series combination having mutual inductance of the coils as M. The equivalent self-inductance of the combination will be:

• A. $\frac{1}{L1 }$_ + $\frac{1}{L2}$ _ + $\frac{1}{M}$
• B. L 1 + L 2 + M
• C. L 1 + L 2 + 2 M
• D. L 1 + L 2 - 2 M

Answer 1

Answer: (D)

L 1 + L 2 - 2 M

Answer 2

Self-inductances are in series but their mutual inductances are linked oppositely so equivalent self-inductance
L = L 1 + L 2 – M – M
L = L 1 + L 2 – 2 M

$\therefore,$ The correct option is (D): $L_1 + L_2 – 2M$