Q.
Two small sphere balls each carrying charges $q = 10\mu$C are suspended by two insulated threads of equal length 1m each, from a point fixed in the ceiling. It is found that in equilibrium, threads are separated by an angle 60${^\circ}$ between them as shown in figure, the tension in the thread is
A) 0.18 N
B) 18 N
C) 1.8 N
D) None of the above
Explanation
(c) Let tension in the thread is $T$, then force of repulsion between the charges.
$\ \ \ F = T\cos\ 60{^\circ}$
Or = $\frac{9 \times 10^{9} \times 10 \times 10^{- 6} \times 10 \times 10^{- 6}}{(1)^{2}}$
$\ \ \ \ \ \ \ = T\cos\ 60{^\circ}$
Or $T \times \frac{1}{2} = 0.9$
$\therefore\ \ \ T = 2 \times 0.9 = 1.8$ N
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.