Question

A wire of fixed length is wound on a solenoid of length l and radius r

Answer 1

A wire of fixed length is wound on a solenoid of length l and radius r. its self inductance is found l . now if same wire is wound on a solenoid of length l/2 and radius r/2, then the self inductance will be
L/2
Explanation:

Self inductance is directly proportional to; n²lr²

hence, the length of the wire is 2πrn1
L1=k n1²lr²

Now, if the same wire is wound on a solenoid of length l/2 and radius r/2.

Number of turns would be; 2πrn1/2πr/2=2n1

Hence, the correct answer is; L/2