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QPage 248: Q5: HC Verma: Concepts of Physics - Volume 2 Magnetic Field Due to a Current Page 248: Q5 Solution: The magnetic field inside a tightly wound, long solenoid is .…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often assume every added turn, even those at the solenoid’s ends, increases the interior field because $B=\mu_0 n i$ appears length‑independent; they forget that $n=N/L$ changes and that the magnetic field of a distant loop drops rapidly, so end turns contribute only weak edge fields that hardly affect the uniform central field.

The magnetic field inside a tightly wound, long solenoid is B=μ0niB = \mu_0 ni. It suggests that the field does not depend on the total length of the solenoid, and hence if we add more loops at the ends of a solenoid the field should not increase. Explain qualitatively why the extra-added loops do not have a considerable effect on the field inside the solenoid.

Step-by-Step Verified Solution

**Answer:** The extra loops at the ends produce fields that are largely along the axis but also have radial components. For a long solenoid, the end effects are negligible compared to the field produced by the central loops. **Step-by-Step Explanation:** The magnetic field inside an ideal infinite solenoid is uniform and given by B=μ0niB = \mu_0 n i. For a finite solenoid, the field near the centre is still approximately uniform. Adding more loops at the ends increases the length but the additional field contribution at the centre is small because those loops are far away. Hence, the field does not increase significantly.

All Questions in this Chapter

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