The Human Eye and the Colourful World Practice Flashcards

This set covers the anatomy of the human eye, vision defects and their correction, optical phenomena like dispersion and atmospheric refraction, and the properties of light scattering.

Retina

A delicate membrane with an enormous number of light-sensitive cells that acts as a screen on which the lens system forms an inverted real image.

Cornea

A thin membrane through which light enters the eye, forming a transparent bulge on the front surface of the eyeball.

Eyeball

A structure approximately spherical in shape with a diameter of about $2.3\,cm$.

Iris

A dark muscular diaphragm located behind the cornea that controls the size of the pupil.

Pupil

A structure that regulates and controls the amount of light entering the eye.

Crystalline lens

The part of the eye that provides the finer adjustment of focal length required to focus objects at different distances on the retina.

Accommodation

The ability of the eye lens to adjust its focal length.

Ciliary muscles

Muscles that modify the curvature of the eye lens; they contract to make the lens thicker for nearby objects and relax to make it thin for distant objects.

Least distance of distinct vision

The minimum distance ($25\,cm$ for a young adult) at which objects can be seen most distinctly without strain; also called the near point.

Far point

The farthest point up to which the eye can see objects clearly; it is infinity for a normal eye.

Cataract

A condition in old age where the crystalline lens becomes milky and cloudy, causing partial or complete loss of vision.

Myopia

Also known as near-sightedness; a defect where a person can see nearby objects clearly but cannot see distant objects distinctly because the image is formed in front of the retina.

Hypermetropia

Also known as far-sightedness; a defect where distant objects are seen clearly but nearby objects are blurred because light rays are focused behind the retina.

Presbyopia

A defect arising with aging due to weakening ciliary muscles and diminishing flexibility of the eye lens, causing the near point to recede.

Bi-focal lenses

Lenses used to correct both myopia and hypermetropia, where the upper portion is a concave lens and the lower part is a convex lens.

Angle of the prism

The angle between the two rectangular lateral faces of a triangular glass prism.

Angle of deviation

The angle between the direction of the incident ray and the emergent ray after passing through a prism, denoted as $\angle D$.

Dispersion

The splitting of light into its component colors, such as when white light passes through a glass prism.

Spectrum

The band of colored components of a light beam.

VIBGYOR

The acronym for the sequence of colors in a spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

Atmospheric refraction

The refraction of light by the earth's atmosphere caused by a medium of gradually changing refractive index.

Tyndall effect

The phenomenon of scattering of light by colloidal particles, which makes the path of a light beam visible.

Rayleigh Scattering Rule (Wavelength Reference)

Fine particles scatter shorter wavelengths (blue) more strongly, while red light has a wavelength about $1.8$ times greater than blue light.

Advance sunrise and delayed sunset

Phenomena caused by atmospheric refraction where the Sun is visible about $2$ minutes before actual sunrise and $2$ minutes after actual sunset.