Two small spherical balls each carrying a charge `Q= 10 mu C`( 10 micro=coulomb) are suspended by two insulating threads of equal lengths `1 cm` each, from a point fixed in the ceiling. It is found that in equilibrium threads are sepreated by an angle `60^(@)` between them, as shown in figure. What is the tension in the threads
(Given `(1)/(4piepsilon_(0))= 9xx10^(9)Nm//C^(2)` )

Options

A. 18 N
B. 1.8 N
C. 0.18 N
D. None of the above

Answer

B

Explanation

`F=T sin theta and sin 30^@ = (r//2)/1 implies r =1m`
`9 xx10^9 xxQ^2/r^2 =T(1)/2 implies 2 xx 9 xx10^9 xx100 xx10^(-12)`
`= 1.8 N`