A point charge is kept at the center of a metallic insulated spherical shell. Then

In the diagram shown $P$, is a point negative charge. Its weight is balanced by the electric force due to the fixed very long wire. The equilibrium of the particle is

A charge $q$ is placed at the center of the cubical vessel (with one face open) as shown in the figure. The flux of the electric field through the surface of the vessel is

A large sheet carries uniform surface charge density $\sigma .$ A rod of length $2\ell$, has a linear charge density $\lambda$, on one half and $-\lambda$, on the second half. The rod is hinged at mid-point $O$, and makes angle $\theta$, with the normal to the sheet. The electric force experienced by the rod is

The figure shows two large, closely placed, parallel, nonconducting sheets with identical (positive) uniform surface charge densities, and a sphere with a uniform (positive) volume charge density. Four points marked as $1, 2, 3$ and $4$ are shown in the space in between. If $E_1, E_2, E_3$ and $E_4$ are the magnitude of net electric fields at these points respectively then: