Figure shows an imaginary cube of side a. A uniformly charged rod of length a moves towards right at a constant speed v. At `t=0` the right end of the just touches the left face of the cube. Plot a graph between electric flux passing through the cube versus time.

Explanation

The electric flux passing through a closed surface depends on the net charge inside the surface. Net charge in this case first increases, reaches a maximum value and finaly decreases to zero. The same is the case with the electric flux. The electric flux `phi` versus time graph is as shown in figure below.