JEE Main & Advanced Physics Magnetism Question Bank Magnetic Equipments

  • question_answer
    Two tangent galvanometers having coils of the same radius are connected in series. A current flowing in them produces deflections of 60° and 45° respectively. The ratio of the number of turns in the coils is [MP PET 1995; MP PMT 1999]

    A)            4/3

    B)            \[(\sqrt{3}+1)/1\]

    C)            \[(\sqrt{3}+1)/(\sqrt{3}-1)\] 

    D)            \[\sqrt{3}/1\]

    Correct Answer: D

    Solution :

               In the first galvanometer \[{{i}_{1}}={{K}_{1}}\tan {{\theta }_{1}}={{K}_{1}}\tan {{60}^{o}}={{K}_{1}}\sqrt{3}\] In the second galvanometer \[{{i}_{2}}={{K}_{2}}\tan {{\theta }_{2}}={{K}_{2}}\tan {{45}^{o}}={{K}_{2}}\] In series i1 = i2 Þ \[{{K}_{1}}\sqrt{3}={{K}_{2}}\Rightarrow \frac{{{K}_{1}}}{{{K}_{2}}}=\frac{1}{\sqrt{3}}\] But \[K\propto \frac{1}{n}\Rightarrow \] \[\frac{{{K}_{1}}}{{{K}_{2}}}=\frac{{{n}_{2}}}{{{n}_{1}}}\]     \ \[\frac{{{n}_{1}}}{{{n}_{2}}}=\frac{\sqrt{3}}{1}\].


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