A small bob is suspended from the roof with a string and hangs vertically. The bob is given a charge +q and a uniform horizontal electric field is set up o the neighbourhood of the bob. Now the bob hangs intjhe field such that the string makes an angle of `30^(@)` with the vertical. If the charge on te bob is made +3q, and the bob once again comes to equilibrium, then the angle made by the string with the vertical will be

Options

A. `30^(@)`
B. `45^(@)`
C. `60^(@)`
D. `90^(@)`

Answer

A

Explanation

Three forces on the bob, T, mg and qE produced equilibrium. Resolving T and appling the condition of equilibrium gives qE=mg tan q.