Two identical charged spheres are suspended by strings of equal lengths. The strings make an angle $\theta$ with each other. When suspended in water the angle remains the same. If density of the material of the sphere is $1.5 \mathrm {~g/cc}$, the dielectric constant of water will be $\_\_\_\_$.\\
(Take density of water $= 1 \mathrm {~g/cc}$)