When considering the arrangement of rods and cones in the retina, there is a central location where only cones are found. As we move farther away from this point there are increasing amounts of rods and fewer cones so, as some point we are only able to see black and white. This central location of only cones is known as the.

stands for electromotive force and it is measured in volts. despite its name, it is not actually the force in the sense of being a "pushing" or "pulling" (not measured in newtons).an equation that relates emf,  ℰ,  to a battery's terminal voltage, v, current, i, and internal resistance, r, is    ℰ = v + irin this case, the emf can be interpreted as a voltage—a difference in electric potential.i would not say that it would be considered an energy. if emf can be defined as the energy/work per a unit charge from a battery or other electric source, then it is not strictly energy.