Consider a long solenoid of length l and radius r. If n is the number of turns per unit length and μ₀ is the permeability of free space, the inductance of the solenoid is: (a) 2μ₀ π n² r² l (b) μ₀ π n² r² l (c) μ₀ n² r² l (d) (μ₀ / 2π) n² r² l

Answer: (b). L = μ₀ n² A l for a long solenoid. A = π r² ⇒ L = μ₀ π n² r² l So the answer is (b) μ₀ π n² r² l.

Consider a long solenoid of length l and radius r. If n is the number… | NEET 2026 (Re-neet)

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Self-Inductance & Energy

Consider a long solenoid of length $l$ and radius $r$ . If $n$ is the number of turns per unit length and $\mu_0$ is the permeability of free space, the inductance of the solenoid is:

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Answer: (b)

$L = \mu_0 n^2 A l$ for a long solenoid.
$A = \pi r^2 \Rightarrow L = \mu_0 \pi n^2 r^2 l$
So the answer is (b) $\mu_0 \pi n^2 r^2 l$ .

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