JEE Main & Advanced Physics Magnetism Question Bank Magnetic Equipments

  • question_answer
    A certain amount of current when flowing in a properly set tangent galvanometer, produces a deflection of 45°. If the current be reduced by a factor of \[\sqrt{3}\], the deflection would [MP PMT 1996; DPMT 2005]

    A)            Decrease by 30°                  

    B)            Decrease by 15°

    C)            Increase by 15°                   

    D)            Increase by 30°

    Correct Answer: B

    Solution :

               In tangent galvanometer, \[I\propto \tan \theta \] \[\therefore \ \frac{{{I}_{1}}}{{{I}_{2}}}=\frac{\tan {{\theta }_{1}}}{\tan {{\theta }_{2}}}\Rightarrow \frac{{{I}_{1}}}{{{I}_{1}}/\sqrt{3}}=\frac{\tan {{45}^{0}}}{\tan {{\theta }_{2}}}\] \[\Rightarrow \sqrt{3}\tan {{\theta }_{2}}=1\Rightarrow \tan {{\theta }_{2}}=\frac{1}{\sqrt{3}}\Rightarrow {{\theta }_{2}}={{30}^{o}}\] So deflection will decrease by 45o- 30o = 15o.


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