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Q129 (NDA-I/2025) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Electricity and magnetism Answer Verified

The magnetic field inside a long straight solenoid-carrying current

Result
Your answer: —  Â·  Correct: D
Explanation

The magnetic field inside a long straight current-carrying solenoid is uniform. This uniformity is characterized by magnetic field lines that are parallel straight lines, indicating that the field strength and direction are the same at all points within the interior [1]. For an ideal or very long solenoid, the field is considered translation-invariant along the axis, meaning every point far from the ends experiences the same magnetic environment. While the field strength does decrease near the ends due to fringe effects—dropping to approximately half its central value at the very exit—the standard physical description for a 'long' solenoid emphasizes the uniform nature of the field within its core. This uniform field is mathematically expressed as B = μ0nI, where 'n' is the number of turns per unit length. This property makes solenoids highly effective for magnetizing materials or focusing particle beams [1].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > 12.2.4 Magnetic Field due to a Current in a Solenoid > p. 201
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