The Human Eye and The Colourful World – Key Vocabulary

Vocabulary flashcards covering major terms and concepts from the chapter on The Human Eye and The Colourful World.

Human Eye

A sensitive sense organ whose lens system forms images on the retina, enabling vision.

Cornea

Transparent, curved front layer of the eye where most refraction of incoming light occurs.

Iris

Dark muscular diaphragm behind the cornea that controls pupil size.

Pupil

Opening in the iris that regulates the amount of light entering the eye.

Retina

Light-sensitive screen at the back of the eye containing photoreceptor cells that generate electrical signals.

Ciliary Muscles

Muscles that adjust the curvature (and focal length) of the eye’s crystalline lens for accommodation.

Accommodation

The eye’s ability to change lens focal length to focus on near and distant objects.

Least Distance of Distinct Vision (Near Point)

Minimum comfortable viewing distance for clear vision, about 25 cm for a normal young adult.

Far Point

The farthest distance at which the eye can see clearly; infinity for a normal eye.

Myopia

Near-sightedness; distant objects focus in front of the retina. Corrected with a concave lens.

Hypermetropia

Far-sightedness; nearby objects focus behind the retina. Corrected with a convex lens.

Presbyopia

Age-related loss of accommodation causing difficulty in seeing near objects; often corrected with bifocals.

Concave Lens (Diverging)

Lens used to spread light rays outward; corrects myopia by moving image back onto the retina.

Convex Lens (Converging)

Lens that brings light rays together; corrects hypermetropia by moving image forward onto the retina.

Bifocal Lens

Eyeglass lens combining concave (upper) and convex (lower) sections to correct both near and far vision.

Cataract

Condition where the eye’s lens becomes cloudy, leading to partial or complete vision loss; treatable by surgery.

Glass Prism

Transparent triangular block with two triangular bases and three rectangular faces that refracts light.

Angle of Prism

The angle between the two refracting lateral faces of a prism.

Angle of Deviation

The angle between the incident ray’s direction and the emergent ray after passing through a prism.

Dispersion

Splitting of white light into its component colours when passing through a prism.

Spectrum

Band of colours (Violet, Indigo, Blue, Green, Yellow, Orange, Red) produced by dispersion of white light.

VIBGYOR

Mnemonic representing the order of colours in the visible spectrum: Violet-Indigo-Blue-Green-Yellow-Orange-Red.

Newton’s Recombination Experiment

Demonstration that a second inverted prism recombines dispersed colours into white light.

Rainbow

Natural spectrum formed by dispersion, internal reflection, and refraction of sunlight in water droplets.

Atmospheric Refraction

Bending of light as it passes through Earth’s atmosphere with varying density.

Twinkling of Stars

Apparent brightness fluctuations due to atmospheric refraction of starlight through turbulent air layers.

Advance Sunrise and Delayed Sunset

Effect where the Sun is seen about 2 minutes earlier at dawn and later at dusk because of atmospheric refraction.

Scattering of Light

Redirection of light by small particles, producing phenomena like blue sky and red sunsets.

Tyndall Effect

Visible path of a beam of light when scattered by colloidal particles in a medium.

Blue Colour of the Sky

Result of preferential scattering of shorter-wavelength blue light by small atmospheric particles.

Red Signal Lights

Use of red light (least scattered by fog/smoke) to ensure visibility over large distances.

Power of a Lens

Measure of a lens’s converging or diverging ability, expressed in dioptres (D), equal to 1/focal length (m).

Angle of Incidence

Angle between the incident ray and the normal to the surface at the point of incidence.

Angle of Refraction

Angle between the refracted ray and the normal inside the medium.

Emergent Ray

Ray that exits an optical medium after refraction, leaving a prism or glass slab.

Eye Donation

Post-death gifting of corneas to restore sight; eyes must be removed within 4–6 hours and can benefit up to four people.