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

When a piece of polythene is rubbed with wool, a negative charge of $$4 \times 10^{-7} \mathrm{C}$$ is developed on the polythene. The number of electrons transferred from wool to polythene is $$[e=1.6 \times\left.10^{-19} \mathrm{C}\right]$$

A hollow metal sphere has a radius 'r'. The potential difference between a point on its surface and at a point at a distance '3r' from its centre is 'V'. The electric intensity at the distance '3r' from the centre of the sphere will be :