Question

Two equal and opposite charges of $ 2\times {{1}^{-10}}C $ are placed at a distance of 1 cm forming a dipole and are placed in a electric field of $ 2\times {{10}^{5}}N\text{/}C $ . The maximum torque on dipole is :

• A. $ 2\sqrt{2}\times {{10}^{-6}}\text{Nm} $
• B. $ 8\times {{10}^{8}}\text{Nm} $
• C. $ 4\times {{10}^{-}}^{7}\text{Nm} $
• D. $ 4\times {{10}^{-}}^{9}\text{Nm} $

Answer 1

Answer: (C)

$ \tau =\overrightarrow{p}\times \overrightarrow{E}=pE\sin \theta $ $ {{\tau }_{\max }}=p\times E $ (As $ \theta =90{}^\circ , $ $ p=ql $ ) $ =ql\times E=2\times {{10}^{-10}}\times 1\times {{10}^{-2}}\times 2\times {{10}^{5}} $ $ =4\times {{10}^{-7}}Nm $