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JEE Main & Advanced Physics Magnetism Question Bank Magnetic Equipments

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    Two magnets are held together in a vibration magnetometer and are allowed to oscillate in the earth's magnetic field with like poles together, 12 oscillations per minute are made but for unlike poles together only 4 oscillations per minute are executed. The ratio of their magnetic moments is [MP PMT 1996; CPMT 2002]

    A)            3 : 1                                          

    B)            1 : 3

    C)            3 : 5                                          

    D)            5 : 4

    Correct Answer: D

    Solution :

               In the sum and difference method of vibration magnetometer \[\frac{{{M}_{1}}}{{{M}_{2}}}=\frac{T_{2}^{2}+T_{1}^{2}}{T_{2}^{2}-T_{1}^{2}}\] Here \[{{T}_{1}}=\frac{1}{{{n}_{1}}}=\frac{60}{12}=5\sec .\ {{T}_{2}}=\frac{1}{{{n}_{2}}}=\frac{60}{4}=15\sec \] \[\therefore \frac{{{M}_{1}}}{{{M}_{2}}}=\frac{{{15}^{2}}+{{5}^{2}}}{{{15}^{2}}-{{5}^{2}}}=\frac{225+25}{225-25}=\frac{5}{4}\]


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