Verified Solution • 2025–26 Session moderate

QPages 277-278: Q24: HC Verma: Concepts of Physics - Volume 2 Permanent Magnets Pages 277-278: Q24 Solution: A bar magnet makes 40 oscillations per minute in an oscillation …

A bar magnet makes 40 oscillations per minute in an oscillation magnetometer. An identical magnet is demagnetized completely and is placed over the magnet in the magnetometer. Find the time taken for 40 oscillations by this combination. Neglect any induced magnetism.

Step-by-Step Verified Solution

**Answer:** Time for 40 oscillations = 402 min40\sqrt{2} \text{ min}. **Step-by-Step Explanation:** When an identical demagnetized magnet is placed over the original, the moment of inertia doubles but the magnetic moment remains the same. T′=2π2IMBH=2TT' = 2\pi \sqrt{\frac{2I}{MB_H}} = \sqrt{2} T. Time for 40 oscillations = 40×2 min40 \times \sqrt{2} \text{ min} [citation:2].

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