Overview: The Human Eye & the Colorful World | Science Class 10 PDF Download

The Human Eye

• The human eye, a vital sense organ, enables us to perceive the colorful world around us.
• Structure of the eye: resembles a camera, with a lens system forming images on the light-sensitive retina.
• Light enters through the cornea, and the crystalline lens adjusts focal length for focusing on different distances.
• Iris, a dark muscular diaphragm behind the cornea, controls the size of the pupil, regulating light entering the eye.
• The eye lens forms an inverted real image on the retina, activating light-sensitive cells, which transmit signals to the brain for interpretation.

Power of Accommodation

• The eye lens, composed of a fibrous, jelly-like material, adjusts its curvature through ciliary muscles.
• Accommodation allows the eye to focus on distant objects (relaxed muscles, thin lens) or nearby objects (contracted muscles, thicker lens).
• The minimum distance for clear vision, called the least distance of distinct vision, is approximately 25 cm.

Defects of Vision and Their Correction

• Common refractive defects: myopia (nearsightedness), hypermetropia (farsightedness), and presbyopia (loss of accommodation with age).
• Correction using concave lenses for myopia, convex lenses for hypermetropia, and bifocal lenses for presbyopia.
• Cataract, a condition where the lens becomes milky and cloudy, causing vision loss, can be corrected through surgery.

Refraction of Light Through a Prism

• A triangular glass prism refracts light, creating a spectrum of colors.
• Activity: Observation of refraction through a prism, demonstrating the angle of deviation.

Dispersion of White Light by a Glass Prism

• Newton's experiment with a prism showed that white light is composed of seven colors.
• Dispersion occurs when light passes through a prism, separating colors based on their different angles of refraction.
• A rainbow is a natural spectrum caused by the dispersion of sunlight through water droplets in the atmosphere.

Atmospheric Refraction

• Atmospheric refraction causes phenomena like twinkling of stars, advance sunrise, and delayed sunset.
• Twinkling occurs due to the continuous refraction of starlight through Earth's atmosphere, causing fluctuations in apparent brightness.
• The Sun appears before sunrise and after sunset due to atmospheric refraction bending light around the curvature of the Earth.

Scattering of Light

Tyndall Effect

• Colloidal particles in the atmosphere cause the scattering of light, making paths visible.
• Tyndall effect is observed in smoke-filled rooms or misty forests, demonstrating light scattering by fine particles.

Why is the Colour of the Clear Sky Blue?

• Molecules and particles in the atmosphere scatter shorter wavelengths (blue) more effectively than longer wavelengths (red), making the sky appear blue.
• The absence of atmosphere would result in a dark sky, as there would be no scattering of light.

Note: Activities and specific questions from the original text have been excluded, focusing on the overview and key points.