The impression of an image on the retina of the human eye persists for about what fraction of a second, allowing us to perceive smooth motion in cinema and animation?

Introduction / Context:
The human eye and brain do not respond to visual changes instantaneously. When an image forms on the retina, its impression persists for a short time even after the object is removed. This phenomenon, sometimes called persistence of vision, allows us to experience a sequence of still images shown rapidly as continuous motion, as in films and animated videos. This question asks you to recall the approximate duration of this persistence.

Given Data / Assumptions:

• The question refers to the persistence time of an image on the retina.
• It is asking for an approximate fractional value in seconds.
• Common textbook value used in basic physics is about one sixteenth of a second.
• The values provided include several simple fractions of a second.

Concept / Approach:
Persistence of vision refers to the short time that an image continues to appear in the eye after the actual object has been removed. Experiments and practical experience in cinema show that if images are flashed on a screen quickly enough, the brain blends them into smooth motion. For standard school level physics, it is accepted that the impression on the retina persists for about 1/16 second. This is why showing 16 or more frames per second can create the illusion of continuous movement. Therefore, among the options, 1/16th of a second is the correct approximate duration.

Step-by-Step Solution:
Step 1: Remember that persistence of vision is a short duration, much less than a full second.Step 2: Recall the commonly quoted textbook value, which is about 1/16 second for image persistence on the retina.Step 3: Compare this with the options 1/10th, 1/8th, 1/16th and 1/5th of a second.Step 4: Recognise that 1/16th matches the standard physics teaching value.Step 5: Understand that longer times like 1/5th second would give too much overlap and would not match actual cinematic practice.Step 6: Conclude that the correct answer is 1/16th of a second.

Verification / Alternative check:
Traditional films use 24 frames per second, and older silent films often used about 16 frames per second or slightly more. At these rates, the change between consecutive frames happens faster than the persistence time, so the brain blends them into apparent continuous motion. If persistence were much longer, the moving images would smear together and appear blurred. If it were much shorter, a higher frame rate would be necessary to achieve smooth motion. The commonly accepted estimate of about 0.06 seconds, roughly 1/16 second, fits this practical experience.

Why Other Options Are Wrong:
1/10th and 1/8th of a second are both longer than 1/16th, and while they are of the same order, the standard value taught in introductory physics is 1/16th. The fraction 1/5th of a second is significantly larger and would produce a different visual effect, leading to more noticeable afterimages and motion blur. Since the question is based on the textbook value and common approximation, 1/16th is correct and the other fractions are considered incorrect here.

Common Pitfalls:
Some students may not remember the exact fraction and may guess a value like 1/10th or 1/8th because they sound familiar. Others may confuse persistence of vision with reaction time of the eye, which is typically longer and describes how quickly we respond to stimuli, not how long a static image stays. To avoid confusion, link persistence of vision specifically with frame rates in movies and the rough value 1/16 second that corresponds with early cinematic technology.

Final Answer:
The impression of an image on the retina persists for about 1/16th of a second.