QPages 285-286: Q4: HC Verma: Concepts of Physics - Volume 2 Magnetic Properties of Matter Pages 285-286: Q4 Solution: A long, straight wire carries a current i. The magnetising…

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QPages 285-286: Q4: HC Verma: Concepts of Physics - Volume 2 Magnetic Properties of Matter Pages 285-286: Q4 Solution: A long, straight wire carries a current i. The magnetising…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often mistake the magnetising field intensity $H$ for the magnetic flux density $B$, assuming the iron rod will amplify $H$. Remember that $H$ is set only by free currents ($H=I/2\pi r$ for a straight wire) and is independent of the surrounding material; the iron changes $B$ via $B=\mu_0(H+M)$, not $H$ itself.

A long, straight wire carries a current i. The magnetising field intensity H is measured at a point P close to the wire. A long, cylindrical iron rod is brought close to the wire, so that the point P is at the centre of the rod. The value of H at P will ___________.