question_answer

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

A) \[\frac{mg}{\sin \theta }\text{ and }\frac{qE}{\cos \theta }\]

B) \[\frac{mg}{\cos \theta }\text{ and }\frac{qE}{\sin \theta }\]

C) \[\frac{mg}{\cos \theta }\text{ and }\frac{qE}{\sin \theta }\]

D) \[\frac{mg}{qE}\]

Correct Answer: B

Solution :

[b] In equilibrium,       \[T\cos \theta =mg\]        ??..(1) \[T\sin \theta =qE\]         ??..(2) From (1), \[T=\frac{mg}{\cos \theta }\] From (2), \[T=\frac{qE}{\sin \theta }\]