Question
An electric dipole, consisting of two opposite charges of $$2 \times {10^{ - 6}}C$$ each separated by a distance $$3\,cm$$ is placed in an electric field of $$2 \times {10^5}\,N/C.$$ Torque acting on the dipole is
A.
$$12 \times {10^{ - 1}}N - m$$
B.
$$12 \times {10^{ - 2}}N - m$$
C.
$$12 \times {10^{ - 3}}N - m$$
D.
$$12 \times {10^{ - 4}}N - m$$
Answer :
$$12 \times {10^{ - 3}}N - m$$
Solution :
$$\eqalign{
& {\text{Charges}}\,\left( q \right) = 2 \times {10^{ - 6}}C, \cr
& {\text{Distance}}\,\left( d \right) = 3\,cm = 3 \times {10^{ - 2}}m\,{\text{and}}\,{\text{electric}}\,{\text{field}}\,\left( E \right) = 2 \times {10^5}\,N/C. \cr
& {\text{Torque}}\,\left( \tau \right) = q.d. \cr
& E = \left( {2 \times {{10}^{ - 6}}} \right) \times \left( {3 \times {{10}^{ - 2}}} \right) \times \left( {2 \times {{10}^5}} \right) \cr
& = 12 \times {10^{ - 3}}N - m \cr} $$