Final Answer:
The pupil dilates when the light is shone and contracts when the light is moved away. So, Option B is correct.
Step-by-step explanation:
When you shine a light into your friend's eye in a dimly lit room, the pupil undergoes a reflexive response known as the pupillary light reflex. The iris, the colored part of the eye, contains two sets of muscles—radial muscles and circular muscles. When light is introduced, the circular muscles contract, causing the pupil to dilate and allowing more light to enter the eye. This is a protective mechanism to optimize vision in low-light conditions.
Conversely, when you move the light away, the circular muscles relax, and the radial muscles contract. This causes the pupil to constrict, reducing the amount of light entering the eye. The speed of these changes is quite rapid, typically occurring within fractions of a second. The process is essential for regulating the amount of light reaching the retina, ensuring optimal vision in varying light conditions.
In mathematical terms, the relationship between the intensity of light (I) and the size of the pupil (P) can be expressed as an inverse square law: I proportional to 1/P². When the light is increased, the denominator decreases, leading to an increase in intensity and pupil dilation. Conversely, when the light is removed, the pupil constricts to limit the incoming light. This physiological response is crucial for maintaining visual acuity and protecting the delicate structures of the eye.