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12th Class Physics Electric Charges and Fields Question Bank MCQ - Electric Charges and Fields

  • question_answer
    An electric dipole is placed at an angle of                                                                              \[30{}^\circ\]  with an electric field of intensity                                                            \[2\times {{10}^{5}}\,N{{C}^{-1}}\] . It experiences a torque equal to 4 Nm. The charge on the dipole if the dipole length is 2 cm is:

    A) B mC                           

    B) 4 mC  

    C) 6 mC                           

    D) 2 mC

    Correct Answer: D

    Solution :

    (d) 2 mC Here,                                       \[E=2\times {{10}^{5}}\,N{{C}^{-1}},\,l=2\,cm\,,\,\tau =4\,Nm\] Torque,                    \[\overrightarrow{\tau }\times \overrightarrow{p}\times \overrightarrow{E};\,\tau =pE\,\sin \theta\]                                  \[\therefore \,\,\,\,\,\,4=p\times 2\times {{10}^{5}}\times \sin \,30{}^\circ\] Or                                                                  \[p=4\times {{10}^{-5}}Cm\]                                                                                \[\therefore\] Charge,                                             \[q=\frac{p}{l}=\frac{4\times {{10}^{-5}}Cm}{0.02\,m}\]                                                               \[=2\times {{10}^{-3}}C=2\,mC\]


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