A simple pendulum of length `l` and bob mass `m` is hanging in front of a large nonconducting sheet having surface charge density `sigma`. If suddenly a charge `+q` is given to the bob `&` it is released from the position shown in figure. Find the maximum angle through which the string is deflected from vertical .
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Answer

`2 tan^(-1) ((sigmaq_(0))/(2in_(0) mg))`

Explanation

From work energy theorem (WET)

`W_(EF)+W_(mg)=Delta KE`
`q_(0) xx sigma/(2 in_(0))xxL sin theta-mgL`
`(1- cos theta)=0`
`=q_(0)xx sigma/(2 in_(0))xxLxx2 "sin" theta/2 "cos" theta/2`
`=mgLxx2 "sin"^(2) (2 theta)/2, "tan" theta/2=sigma/(2 in_(0))xxq_(0)/(mg)`