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

Answer 1

Answer: (D)

Current on both the inductor is in opposite direction.
Hence : $L _{ eq }= L _{1}+ L _{2}-2 M$