A volume charge distribution in free space is characterized by the density rho v = q 2Ad exp (− |z| / d ) where d is a distance along z, A is the area of a surface parallel to the xy plane, and q is a fixed charge quantity. The charge distribution exists everywhere. (a) Find the electric field intensity, E, everywhere. (b) What is the interpretation of q?

answer: the correct answer for the fill in the blank is rods.

rods are the specialized photoreceptor cells that are present in the retina of human eye. they are responsible for vision in the night time ( also called scotopic vision). they have very low visual acuity and color distinguishing ability.

as they are responsible for vision in night time, therefore they are found predominantly in the nocturnal animals.