NEET Sample Paper NEET Sample Test Paper-47

  • question_answer
    Two opposite and equal charge \[4 \times {{10}^{-8}}\]when placed\[2 \times {{10}^{-2}}\]cm away, form a dipole. If this dipole is placed in an external electric field\[4 \times {{10}^{8}}\]N/C, the value of maximum torque and the work done in rotating it through \[180{}^\circ \] will be:

    A) \[64\times {{10}^{-4}}\operatorname{N}-m and 64\times 1{{0}^{-4}}\operatorname{J}\]

    B) \[64\times {{10}^{-4}}\operatorname{N}-m and 32\times 1{{0}^{-4}}\operatorname{J}\]

    C) \[32\times {{10}^{-4}}\operatorname{N}-m and 32\times 1{{0}^{-4}}\operatorname{J}\]

    D) \[32\times {{10}^{-4}}\operatorname{N}-m and 64\times 1{{0}^{-4}}\operatorname{J}\]

    Correct Answer: D

    Solution :

    Torque will be maximum when 6 = 90 \[{{\tau }_{max}}=PES\,\,in\,9{{0}^{o}}\] \[=q\ell \operatorname{E} \,\,\,\therefore \left( P=q\times \ell  \right)\] \[=4\times 1{{0}^{-8}}\times 2\times 1{{0}^{-4}}\left( m \right)\times 4\times {{10}^{8}}\] \[=32\times {{10}^{-4}}N-m\] \[\operatorname{W}=PE\left[ cos{{\theta }_{1}}-cos{{\theta }_{2}} \right]\] Note: When nothing is specified assume \[{{\theta }_{1}} =0{}^\circ ,\,\,{{\theta }_{2}} =180{}^\circ \] \[=PE\left[ cos0{}^\circ -cos180{}^\circ  \right]\] \[=PE\left[ 1-cos180{}^\circ  \right]\Rightarrow 2PE\] \[\operatorname{W}=64\times {{10}^{-4}}N-m\]


You need to login to perform this action.
You will be redirected in 3 sec spinner