10th Class Science Electricity and Circuits Question Bank Electricity

  • question_answer
    When the radius of the circular current carrying coil is doubled and the current in it is Halved then magnetic dipole moment of the coil originally four units becomes               

    A)  4 units                 

    B)               8 units                   

    C)               16 units                            

    D)  32 units                     

    Correct Answer: B

    Solution :

                    \[M=niA=ni(\pi {{r}^{2}})\] \[\therefore \]  \[\frac{{{M}_{1}}}{{{M}_{2}}}=\frac{{{i}_{1}}{{r}_{1}}^{2}}{{{i}_{2}}{{r}_{2}}^{2}}\] \[\Rightarrow \]               \[{{M}_{2}}={{M}_{1}}\left( \frac{{{i}_{2}}{{r}_{2}}^{2}}{{{i}_{2}}{{r}_{1}}^{2}} \right)\] Given:   \[{{i}_{2}}=\frac{{{i}_{1}}}{2}\]and\[{{r}_{2}}=2{{r}_{1}}\] \[\therefore \]  \[{{M}_{2}}=4\frac{({{i}_{1}}/2){{(2{{r}_{1}})}^{2}}}{{{i}_{1}}{{r}_{1}}^{2}}=8\]


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