Question

Three identical small balls each of mass m are suspended at one point on silk threads of $l$. Charge on each ball is q and each thread makes same angle $\theta$ with vertical, then

• A. If $\theta ={30}^{\circ }$, tension in threads is $T=\frac{8}{\sqrt{3}}\frac{k{q}^2}{l^2}$.
• B. Separation between balls is $\frac{\sqrt{3}}{2}l$ if $\theta ={30}^{\circ }$.
• C. Tension in threads is $T=\frac{2mg}{\sqrt{3}}$ if $\theta ={30}^{\circ }$.
• D. Tension in threads is $T=\frac{mg}{2}$ if $\theta ={30}^{\circ }$.

Answer 1

Answer: (A), (B), (C)

The correct options are
A If $\theta ={30}^{\circ }$, tension in threads is $T=\frac{8}{\sqrt{3}}\frac{k{q}^2}{l^2}$.
B Separation between balls is $\frac{\sqrt{3}}{2}l$ if $\theta ={30}^{\circ }$.
C Tension in threads is $T=\frac{2mg}{\sqrt{3}}$ if $\theta ={30}^{\circ }$.


$Tcos\theta =mg$ ....... (1)



$x=\sqrt{3}lsin\theta$
$Tsin\theta =2Fcos{30}^{\circ }$
$Tsin\theta =2\frac{k{q}^2}{3l^{2}si{n}^2\theta }\frac{\sqrt{3}}{2}$ ....(2)