Chapter 10: The Human Eye and the Colourful World

Comprehensive vocabulary flashcards covering key definitions, optical defects, ray diagrams, and natural optical phenomena from Class X Physics Chapter 10: The Human Eye and the Colourful World.

Human Eye Anatomy

The structure of the human sense organ that enables vision, consisting of components such as the cornea, iris, pupil, crystalline lens, ciliary muscles, retina, and optic nerve.

Crystalline Lens

A lens composed of a fibrous, jelly-like material that provides the finer adjustment of focal length required to focus objects at different distances on the retina.

Cornea

A thin membrane through which light enters the eye, where most of the refraction for incoming light rays occurs at its outer surface.

Eyeball

An approximately spherical structure forming a transparent bulge on its front surface with a diameter of about $2.3\,\text{cm}$.

Iris

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

Pupil

The aperture in the eye that regulates and controls the amount of light entering the eye.

Retina

A delicate light-sensitive screen containing an enormous number of light-sensitive cells that get activated upon illumination to generate electrical signals sent to the brain via the optic nerve.

Power of Accommodation

The ability of the eye lens to adjust its focal length using the ciliary muscles to focus on distant or nearby objects.

Near Point of the Eye

The minimum distance at which objects can be seen most distinctly without strain (least distance of distinct vision), which is about $25\,\text{cm}$ for a young adult with normal vision.

Far Point of the Eye

The farthest point up to which the eye can see an object clearly, which 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, which can be restored through cataract surgery.

Myopia

A refractive defect (near-sightedness) where nearby objects are seen clearly but distant objects cannot be seen distinctly; caused by excessive curvature of the eye lens or elongation of the eyeball, and corrected using a concave (diverging) lens.

Hypermetropia

A refractive defect (far-sightedness) where distant objects are seen clearly but nearby objects cannot be seen distinctly; caused by the focal length of the eye lens being too long or the eyeball being too small, and corrected using a convex (converging) lens.

Presbyopia

A vision defect arising from ageing where the power of accommodation decreases and the near point recedes due to the gradual weakening of ciliary muscles and diminishing flexibility of the eye lens.

Bi-focal Lenses

Corrective eyeglasses consisting of both concave and convex lenses, where the upper concave part facilitates distant vision and the lower convex part facilitates near vision.

Triangular Glass Prism

An optical medium having two triangular bases and three rectangular lateral surfaces that are inclined to each other.

Angle of the Prism

The angle between the two lateral faces of a triangular glass prism ($\angle A$).

Angle of Deviation

The angle ($\angle D$) between the direction of the incident ray and the emergent ray caused by the peculiar shape of a prism.

Dispersion

The splitting of white light into its component colours when passing through a medium like a glass prism.

Spectrum

The band of coloured components of a light beam formed when white light is split by a prism.

VIBGYOR

The acronym representing the sequence of the seven colours of the spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

Recombination of White Light

The phenomenon demonstrated by Isaac Newton where a second identical inverted prism placed in the path of dispersed spectrum colours recombines them into a beam of white light.

Rainbow

A natural spectrum appearing in the sky opposite the Sun caused by the refraction, dispersion, and internal reflection of sunlight by tiny spherical atmospheric water droplets acting like small prisms.

Atmospheric Refraction

The refraction of light caused by the Earth's atmosphere having air layers of varying temperatures, densities, and changing refractive indices.

Twinkling of Stars

The apparent flickering in brightness and fluctuation in apparent position of point-sized starlight caused by continuous atmospheric refraction through non-stationary layers of air.

Advance Sunrise and Delayed Sunset

The optical phenomenon where the Sun is visible about $2\,\text{minutes}$ before actual sunrise and about $2\,\text{minutes}$ after actual sunset due to atmospheric refraction bending the rays toward the observer.

Scattering of Light

The phenomenon in which light is absorbed by particles of a medium and subsequently radiated in a particular direction, with intensity depending on particle size and wavelength.

Tyndall Effect

The optical phenomenon where the path of a light beam becomes visible due to diffuse reflection and scattering of light by colloidal particles.

Danger Signal Light

Red light utilized for warning signals because its longer wavelength (about $1.8$ times greater than blue light) causes it to be least scattered by fog or smoke, remaining visible over large distances.