question_answer

The bob of a simple pendulum has mass 2g and a charge of \[5.0\mu C.\]It is at rest in a uniform horizontal electric field of intensity 2000 V/m. At equilibrium, the angle that the pendulum makes with the vertical is: \[(take\,g=10m/{{s}^{2}})\]                                    [JEE Main 8-4-2019 Morning]

A) \[{{\tan }^{-1}}(5.0)\]                     

B) \[{{\tan }^{-1}}(2.0)\]

C) \[{{\tan }^{-1}}(0.5)\]         

D) \[{{\tan }^{-1}}(0.2)\]

Correct Answer: C

Solution :

            \[\tan \theta =\frac{qE}{mg}=\frac{5\times {{10}^{-6}}\times 2000}{2\times {{10}^{-3}}\times 10}\]             \[\tan \theta =\frac{1}{2}\Rightarrow \,\theta ={{\tan }^{-1}}(0.5)\]