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In a solenoid, the current flowing through the wire is I and number of

June 1, 2025 by rawan239

In a solenoid, the current flowing through the wire is I and number of turns per unit length is n. This gives a magnetic field B inside the solenoid. If number of turn per unit length is increased to 2n, what will be the value of magnetic field in the solenoid?

B

2B

B/2

B/4

This question was previously asked in

UPSC NDA-1 – 2017

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The correct answer is 2B. The magnetic field inside a long solenoid is directly proportional to the number of turns per unit length and the current flowing through the wire.

The formula for the magnetic field inside an ideal long solenoid is B = μ₀ * n * I, where μ₀ is the permeability of free space, n is the number of turns per unit length, and I is the current. If the number of turns per unit length is increased to 2n while the current I remains the same, the new magnetic field B’ will be B’ = μ₀ * (2n) * I = 2 * (μ₀ * n * I).

Since the original magnetic field was B = μ₀ * n * I, the new magnetic field is B’ = 2B. The magnetic field strength inside a solenoid can be increased by increasing the current, increasing the number of turns per unit length, or by inserting a core material with a higher permeability (like iron) into the solenoid.

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