Question

The coil is wound on an iron core and looped back on itself so that core has two sets of closely wound coils carrying current in opposite directions. The self inductance is

• A. $0$
• B. $2L$
• C. $2L+M$
• D. $L+2M$

Answer 1

Answer: (A)

$0$

Let the inductance due to first loop alone be $L$.

Then inductance due to second loop alone is also $L$.

The effective self inductance can be calculate by: $L_{eff}=L_1+L_2-2M$$=L+L-2\sqrt{L.L}=0$