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Two opposite and equal charges $4 \times {10^{ - 8}}\, coulomb$ when placed $2 \times {10^{ - 2}}\,cm$ away, form a dipole. If this dipole is placed in an external electric field $4 \times 10^8\, newton / coulomb$ , the value of maximum torque and the work done in rotating it through $180^o$ will be
$64 \times {10^{ - 4}}\,Nm$ and $64 \times {10^{ - 4}}\,J$
$32 \times {10^{ - 4}}\,Nm$ and $32 \times {10^{ - 4}}\,J$
$64 \times {10^{ - 4}}\,Nm$ and $32 \times {10^{ - 4}}\,J$
$32 \times {10^{ - 4}}\,Nm$ and $64 \times {10^{ - 4}}\,J$
Solution
$\tau_{\max }=\mathrm{q}(2 \mathrm{a}) \mathrm{E}=4 \times 10^{-8} \times 2 \times 10^{-4} \times 4 \times 10^{8}$
$\Rightarrow \tau_{\max }=\rho \mathrm{E}=32 \times 10^{-4} \mathrm{\,Nm}$
$\mathrm{W}=2 \mathrm{\,pE}=64 \times 10^{-4} \mathrm{\,J}$
