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Two opposite and equal charges $4 \times 10^{-8}$ coulomb when placed $2 \times 10^{-2} \mathrm{~cm}$ 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 $180^{\circ}$ will be
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$32 \times 10^{-4} \mathrm{Nm}$ and $64 \times 10^{-4} \mathrm{~J}$
Dipole moment $p=4 \times 10^{-8} \times 2 \times 10^{-4}=8$ $\times1.0^{-12} \mathrm{~m}$
Maximum torque $=p E=8 \times 10^{-12} \times 4 \times 1$
$=32 \times 10^{-4} \mathrm{Nm}$
Work done in rotating through $1.80^{\circ}=2 p E$
$=2 \times 32 \times 10^{-4}=64 \times 10^{-4} \mathrm{~J}$
Maximum torque $=p E=8 \times 10^{-12} \times 4 \times 1$
$=32 \times 10^{-4} \mathrm{Nm}$
Work done in rotating through $1.80^{\circ}=2 p E$
$=2 \times 32 \times 10^{-4}=64 \times 10^{-4} \mathrm{~J}$
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