The charges $$2 \mathrm{q},-\mathrm{q},-\mathrm{q}$$ are located at the vertices of an equilateral triangle. At the circumcentre of the triangle

A solid metallic sphere has a charge $$+3 Q$$. Concentric with this sphere is a conducting spherical shell having charge $$-\mathrm{Q}$$. The radius of the sphere is '$$A$$' and that of the spherical shell is '$$B$$'. $$(B > A)$$. The electric field at a distance '$$\mathrm{R}$$' $$(\mathrm{A} < \mathrm{R} < \mathrm{B})$$ from the centre is ( $$\varepsilon_0=$$ permittivity of vacuum)

If the radius of the spherical gaussian surface is increased then the electric flux due to a point charge enclosed by the surface

Three equal charges '$$\mathrm{q}_1$$', '$$^{\prime} \mathrm{q}_2$$' and '$$\mathrm{q}_3$$' are placed on the three corners of a square of side 'a'. If the force between $$\mathrm{q}_1$$ and $$\mathrm{q}_2$$ is '$$\mathrm{F}_{12}$$' and that between $$\mathrm{q}_1$$ and $$\mathrm{q}_3$$ is '$$\mathrm{F}_{13}$$', then the ratio of magnitudes $$\left(\frac{F_{12}}{F_{13}}\right)$$ is