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The self-inductance L of a solenoid of length l and area of cross-section A increases if ______. (The number of turns N is fixed.)

Asked in GUJCET 2021 · Coil geometry, cores and combinations

Answer: (3) l decreases and A increases

Step-by-step solution

Idea: for a long solenoid, L = (μ₀N²A)/l.

With N fixed, L ∝ A/l: it grows with the area and falls with the length.

The only option in which both changes raise L is: A increases and l decreases.

So L increases when l decreases and A increases.

Why the other options are wrong

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