Question

The image on the retina remains for:
A) $20s$
B) $10s$
C) $\dfrac{1}{{10}}s$
D) $\dfrac{1}{{16}}s$

Answer 1

The retina is a very important part of an eyeball. It is made up of a few optic sensitive cells and directly connected to the optic nerve.
While the image of an object is created on the retina, the vision created by the optic nerves in the brain does not vanish instant after the displacement of the object. The image persists for some fixed time – this is called the persistence of vision.

Complete answer:
The eyeball has many parts having different activities. The retina is one of the most important parts of the eyeball that is made up of some optic sensitive cells and systems. It is connected to the optical nerve directly.
The image of an object is created on the Retina by the eye lens. Then this feeling is reached to the brain through the optic nerve and hence we can visualize.
The vision that is created in the brain after making the image on the retina does not vanish instantly after the displacement of the object. It remains $\dfrac{1}{{10}}$ seconds in the brain – this phenomenon is called persistence of vision. That’s why We can not understand two different things that happened within the $\dfrac{1}{{10}}$ seconds. The two cases seem to us a single one.
So, the image on the retina remains for $\dfrac{1}{{10}}$ seconds.

Hence, the right answer is in option (C).

Note: Due to the persistence of vision, we can not see the blades of a fan that move at a high speed. The blades are situated at different places at different times, but we see them like they all are the same place in the circular path.
In theatre, the consistent pictures we see are for this persistence of vision. Such as, when walking the positions of the hand, leg, and the body is changed continuously. If we see some still photos of these changes at the same place i.e. on the screen, it seems the person is walking, we cannot feel the existence of each different still photo – this happens due to the persistence of vision.