Question

Two identical non-conducting solid spheres of same mass and charge are suspended in air from a common point by two non-conducting, massless strings of same length. At equilibrium, the angle between the strings is $\alpha$. The spheres are now immersed in a dielectric liquid of density $800\, kg \,m ^{-3}$ and dielectric constant $21$ . If the angle between the strings remains the same after the immersion, then

• A. electric force between the spheres remains unchanged
• B. electric force between the spheres reduces
• C. mass density of the spheres is $840 \,kg\, m ^{-3}$
• D. the tension in the strings holding the spheres remains unchanged

Answer 1

Answer: (A), (C)

$\tan \alpha=\frac{F}{m g}=\frac{F / K}{m g-\rho_{t} v g}$
$\Rightarrow \rho_{0}=840\, kg / m ^{3}$
$T_{1} \cos \alpha=m g, T_{2} \cos \alpha=m g-\rho_{t} v g$
So, $T _{2}$ will decrease