The SI unit of the intensity of electric field is .

The name of the physical quantity whose unit is $\mathrm{Joule} {\left(\mathrm{coulomb}\right)}^{-1}$ is _____.

Figure shows line of constant potential in a region in which an electric field is present. The values of the potentials are written in brackets of the points A,B and C, the magnitude of the field is greatest at the point _____.

A point charge q moves from point P to point S along the path $\mathrm{PQRS}$ (Fig. $2.103$ ) in a uniform field $\overrightarrow{\mathrm{E}}$ pointing parallel to the positive direction of $X$ -axis. The coordinates of P, Q, R and S are $(a, b, 0),(2 a, 0,),$ $(a, b, 0)$ and $(0,0,0)$ respectively. The work done by the field in the above process is given by the expression _____.