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

The Human Eye

• The human eye is a crucial sense organ that helps us see the vibrant world around us.
• Its structure is similar to a camera, with a lens system that projects images onto the light-sensitive retina.
• Most of the bending of light rays happens at the front surface of the cornea.
• Light enters through the cornea, while the crystalline lens fine-tunes the focus for objects at various distances.
• The iris, a dark muscle behind the cornea, regulates the size of the pupil, controlling the light that enters.
• The lens creates an upside-down image on the retina, which is a thin membrane filled with many light-sensitive cells.
• These cells send electrical signals to the brain via the optic nerves, allowing us to see and understand our surroundings.

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 vision problems include myopia (nearsightedness), hypermetropia (farsightedness), and presbyopia (age-related loss of accommodation).
• Myopia is corrected with concave lenses, hypermetropia with convex lenses, and presbyopia with bifocal lenses.
• Cataract occurs when the lens becomes cloudy, leading to vision loss, and can be treated with 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 demonstrated that white light consists of seven colours: Violet, Indigo, Blue, Green, Yellow, Orange, and Red. You can remember the order using the acronym VIBGYOR.
• Dispersion happens when light travels through a prism, separating colours due to varying angles of refraction.
• A rainbow is a natural spectrum seen in the sky after rain, caused by the dispersion of sunlight through tiny water droplets in the atmosphere. It always appears in the opposite direction of the Sun.

Atmospheric Refraction

• Atmospheric refraction creates effects like the twinkling of stars, earlier sunrises, and later sunsets.
• You may notice objects appearing to flicker when viewed through a hot air stream above a fire or radiator. The air above the fire is hotter and less dense than the cooler air above it, affecting its refractive index.
• The Sun is visible before sunrise and after sunset due to this bending of light around the Earth's curvature.

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.