If the number of turns per unit length of a coil of solenoid

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If the number of turns per unit length of a coil of solenoid is doubled, the self-inductance of the solenoid will

1. remain unchanged
2. be halved
3. be doubled
4. become four times

Correct Option: D

Self inductance of a solenoid

=	μn²A
	ℓ

So, self induction ∝ n²
So, inductance becomes 4 times when n is doubled.