Two identical pith balls are charged by rubbing against each other. They are suspended from a horizontal rod through two strings of length 20 cm each, the separation between the susjpension points being 5 cm. in equilibrium, the separation between the balls in 3 cm. Find the mass of each ball and the tension in the strings. the charge on each ball gas a magnitude `2.0 xx 10^(-8) C.`

Explanation

As the balls are rubbed against each other they will acquire equal and opposite charges. The FBD of left ball is shown in figure which shows all the forces acting on ball in equilibrium position.


Here for equilibrium of each bob. we have
or `T sin theta=(kq^2)/(r^2)" "...(1)`
or `Tcostheta=mg" "...(2)`
or `tantheta=(kq^2)/(r^2mg)`
or `1/(sqrt((20)^(2)-1^2))=(K(2xx10^(-8))^(2))/((3xx10^(-2))mxx10)`
or `m = 7.96m`
From equation (2)
From equation (2)
`T=(mg)/(costheta)=(7.96xx10^(-3)xx10xx20)/(sqrt((20)^(2))-1)`
`=7.72xx10^(-2)N`