Which of the following equations represents the Gauss's law in a homogeneous isotropic medium?

An electrostatic potential is given by $$\phi=2x\sqrt y$$ volt in the rectangular co-ordinate system. The magnitude of the electric field at x = 1 m,y = 1 m is _________V/m

In the circuit shown in fig, $$L$$ is large and the average value of $$'i'$$ is $$100A.$$ The thyristor is gated in the half cycle of $$'e'$$ at a delay angle $$\alpha $$ equal to ___________.
$$e\left( t \right) = \sqrt 2 .00\,\,\sin \,\,314t$$

The inductance of a power transmission line increases with