Figure shown an imaginary cube of edge L/2. A uniformly Charged rod of length L moves towards left at a small but constant speed v. At t=0, the left end just touches the centre of the cube opposite it. Which of the graphs shown in figure represents the flux of the electic field through the cube as the rod goes through it?

Explanation

As the rod enters the box, the charge increases,
hence, flux increases linearly. When rod enters the
cube completely, the charge within the cube becomes
constant for sometime and hence the flux also becomes
constant.
When the rod starts moving out of the cube, the charge
inside the cube starts decreasing and hence the flux will
also start decreasing linearly. Hence, graph d is the
current graph.