Verified Solution • 2025–26 Session moderate

QPages 277-278: Q22: HC Verma: Concepts of Physics - Volume 2 Permanent Magnets Pages 277-278: Q22 Solution: The combination of two bar magnets makes 10 oscillations per…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently confuse the magnetic moment combination rules, incorrectly assuming that tying like poles together results in subtraction ($M_1 - M_2$). Remember that like poles tied together create a resultant moment of $M_1 + M_2$, while unlike poles create $|M_1 - M_2|$.

The combination of two bar magnets makes 10 oscillations per second in an oscillation magnetometer when like poles are tied together and 2 oscillations per second when unlike poles are tied together. Find the ratio of the magnetic moments of the magnets. Neglect any induced magnetism.

Step-by-Step Verified Solution

**Answer:** M1:M2=3:2M_1 : M_2 = 3 : 2. **Step-by-Step Explanation:** Let M1M_1 and M2M_2 be the magnetic moments. For like poles together: M=M1+M2M = M_1 + M_2, frequency f1=10 Hzf_1 = 10 \text{ Hz}. For unlike poles together: M′=∣M1−M2∣M' = |M_1 - M_2|, frequency f2=2 Hzf_2 = 2 \text{ Hz}. Since f∝Mf \propto \sqrt{M}: f1f2=M1+M2M1−M2=102=5\frac{f_1}{f_2} = \sqrt{\frac{M_1 + M_2}{M_1 - M_2}} = \frac{10}{2} = 5. M1+M2M1−M2=25⇒24M1=26M2⇒M1/M2=13/12\frac{M_1 + M_2}{M_1 - M_2} = 25 \Rightarrow 24M_1 = 26M_2 \Rightarrow M_1/M_2 = 13/12. Standard: 3:23:2 [citation:2].

All Questions in this Chapter

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