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 $800kg{m}^{-3}$ 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 $840kg{m}^{-3}$
• D. the tension in the strings holding the spheres remains unchanged

Answer 1

Answer: (A), (C)

$\tan \alpha =\frac{F}{mg}=\frac{F/K}{mg-{\rho }_{t}vg}$
$\Rightarrow {\rho }_0=840kg/m^3$
$T_1\cos \alpha =mg,T_2\cos \alpha =mg-{\rho }_{t}vg$
So, $T_2$ will decrease