Optics of the Human Eye & Related Atmospheric Phenomena

Vocabulary flashcards covering structure and function of the human eye, common vision defects and their corrections, optical phenomena such as dispersion and total internal reflection, and atmospheric effects on light.

Human Eye

Sense organ that enables vision; situated in skull eye sockets with a constant diameter of about 2.3 cm throughout life.

Sclera

The tough, opaque, outermost white layer of the eye that protects and maintains its shape.

Cornea

Transparent, outermost part of the eye that provides most of the eye’s refraction of incoming light.

Eye Lens

Convex, flexible, jelly-like structure that focuses a real, inverted image on the retina by changing curvature.

Iris

Dark, muscular diaphragm that controls pupil size and thus regulates the amount of light entering the eye.

Pupil

Central aperture within the iris—often called the "window" of the eye—that admits light.

Ciliary Muscles

Muscles that hold the lens and alter its curvature to adjust focal length during accommodation.

Retina

Delicate, light-sensitive membrane containing rods and cones where images are formed for transmission to the brain.

Optic Nerve

Nerve bundle that carries visual information from the retina to the brain’s visual centers.

Blind Spot

Point on the retina where the optic nerve exits; contains no photoreceptors, so no image is detected there.

Aqueous Humour

Clear fluid between cornea and lens that helps focus light on the retina and nourishes eye tissues.

Vitreous Humour

Gel-like fluid filling the space between the lens and retina, helping maintain eyeball shape.

Far Point

Maximum distance at which the eye can see clearly; for a normal eye, effectively at infinity.

Near Point (Least Distance of Distinct Vision)

Minimum distance (about 25 cm for a normal eye) at which an object can be seen clearly without strain.

Accommodation

Process by which ciliary muscles change lens curvature and focal length to keep images focused on the retina.

Focusing on Far Objects

Ciliary muscles relax, lens becomes thin, focal length increases to bring distant images onto the retina.

Focusing on Near Objects

Ciliary muscles contract, lens thickens, focal length decreases to focus nearby images on the retina.

Myopia (Near-Sightedness)

Defect where nearby objects appear clear but distant ones appear blurred because images form in front of the retina.

Causes of Myopia

Excessive curvature of the eye lens or elongation (stretching) of the eyeball.

Correction of Myopia

Use of a concave (diverging) lens to form a virtual image at the eye’s far point, shifting focus onto the retina.

Hypermetropia (Far-Sightedness)

Defect where distant objects are clear but near ones are blurred because images form behind the retina.

Causes of Hypermetropia

Eye lens focal length too long or eyeball too short.

Correction of Hypermetropia

Use of a convex (converging) lens to help form a real image of a near object directly on the retina.

Dispersion of Light

Splitting of white light into constituent colours when passing through a prism due to different refractive indices.

Prism

Transparent optical element with flat, polished surfaces that refracts and disperses light into a spectrum.

Total Internal Reflection (TIR)

Phenomenon in which light incident on a boundary from a denser to a rarer medium reflects entirely back when the incidence angle exceeds the critical angle.

Conditions for TIR

(1) Light travels from denser to rarer medium; (2) angle of incidence is greater than the critical angle.

Rainbow Formation

Sequence of refraction, internal reflection, and dispersion of sunlight in water droplets producing a visible spectrum arc.

Atmospheric Refraction

Bending of light as it travels through layers of air with varying optical densities, causing apparent position shifts of celestial objects.

Blue Colour of Sky

Due to Rayleigh scattering: shorter-wavelength blue light is scattered more by tiny atmospheric particles than longer wavelengths.

Reddish Sunrise & Sunset

Sun’s rays traverse more atmosphere near the horizon; shorter wavelengths scatter away, leaving predominantly red light.

Red for Danger Signals

Red light has the longest wavelength, scatters least, and remains visible over longer distances in atmosphere, enhancing safety.

Yellow School Buses

Yellow has high visibility and peripheral detection; its medium wavelength scatters moderately, making buses noticeable in various conditions.

Apparent Raising of Celestial Bodies

Stars and Sun appear slightly higher than actual positions because atmospheric refraction bends their light downward.

Early Sunrise & Delayed Sunset

Atmospheric refraction allows the Sun to be seen about two minutes earlier at dawn and later at dusk than its geometric position.

Twinkling of Stars

Rapid changes in apparent brightness caused by atmospheric turbulence refracting starlight along varying paths.

Planets Do Not Twinkle

Planets’ apparent disks average out atmospheric fluctuations, so their brightness appears steady compared to point-like stars.