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A ball at O is in equilibrium as it is attached with two strings AO and DO, which are tied atA and D. AO = DO= a(sqrt5). The charges at A, B, C, abd D are +q, +Q, +2Q, and -q, respectively. Find the correct options. The ball at O is positively charged. |
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Answer» The ball O cannot remain in equilibrium. For ball `O` (positively charged) to be in equilibrium at the middle of `BC`  `[(q)/(4piepsilon_(0)(asqrt(5))^(2))+(q)/(4piepsilon_(0)(asqrt(5))^(2))]cos theta+(Q)/(4piepsilona^(2))` `=(2Q)/(3piepsilon_(0)a^(2))` `q=(5sqrt(5)Q)/(2)`(as `cos theta=(a)/(asqrt(5)`) If `q=5sqrt(5)Q//2,` ball will be in equilibrium , even if charge are interchanged (a) is WRONG and (c) and (d) are CORRECT. If charge as `C` is `+Q`, then `(2qcostheta)/(5)+Q=Q` or `(2qcostheta)/(5)=0` `Qcancel=0,theta=90^(@)`, which is not possible (b) is wrong. |
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