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NDA 1 2025 GAT, question 129

Topic: Physics

Q129

The magnetic field inside a long straight solenoid-carrying current

  1. (a) is zero
  2. (b) decreases as we move towards its end
  3. (c) increases as we move towards its end
  4. (d) is uniform inside the solenoidCorrect answer

Solution.

Answer: (d) is uniform inside the solenoid

  1. For a long solenoid, the interior field away from its ends is approximately uniform: B=μ0nIB = \mu_{0}nI for an air core, where nn is the number of turns per unit length.
  2. The field lines there are nearly parallel and equally spaced.