Question

A pendulum bob of mass m carrying a charge q is at rest with its string making all angle $\theta$ with the vertical in a uniform horizontal electric field E. The tension in the string is :

• A. $\frac{mg}{sin\theta }$
• B. $mg$
• C. $\frac{qE}{sin\theta }$
• D. $\frac{qE}{cos\theta }$

Answer 1

The correct option is C $\frac{qE}{sin\theta }$

Let T be the tension in the string.

In equilibrium , $mg=T\cos \theta \Rightarrow T=\frac{mg}{\cos \theta }$ and $qE=T\sin \theta \Rightarrow T=\frac{qE}{\sin \theta }$