Two identical He-filled spherical balloons each carrying a charge q are tied to a weight W with strings and float in equilibrium, as show in fig. (a)
Find the magnitude of q, assuming that the charge on each balloon acts as if it were concentrated at the centre.

Explanation

`2Tcostheta=W,Tsintheta=F`
or `(tantheta)/(2)=(F)/(W)orF=W(tantheta)/(2)`
or `(q^(2))/(4piepsilon_(0)(2x)^(2))=(Wtantheta)/(2)orq=sqrt(8Wtanthetapiepsilon_(0)x^(2))`