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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.

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

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.

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

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.

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

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.

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FAQs on Overview: The Human Eye & the Colorful World - Science Class 10

1. What are the common defects of vision and how can they be corrected?
Ans. The common defects of vision include myopia (nearsightedness), hyperopia (farsightedness), and presbyopia (loss of near vision with age). These defects can be corrected using spectacles or contact lenses. Myopia can also be corrected through refractive surgeries like LASIK.
2. How does a prism refract light?
Ans. A prism refracts light by bending it towards the base of the prism. This happens because light travels at different speeds in different mediums, and when it enters the prism, it slows down and changes direction due to the change in medium.
3. What is the process of dispersion of white light by a glass prism?
Ans. The process of dispersion occurs when white light passes through a glass prism. The different colors of the spectrum have different refractive indices, causing them to bend at different angles. This separation of colors results in the dispersion of white light into its constituent colors.
4. How does atmospheric refraction affect the appearance of celestial objects?
Ans. Atmospheric refraction is the bending of light as it passes through the Earth's atmosphere. It causes celestial objects to appear higher in the sky than they actually are. This is why the Sun appears to rise before it actually crosses the horizon and why the stars twinkle.
5. What is the phenomenon of scattering of light?
Ans. Scattering of light is the phenomenon where light is redirected in different directions as it passes through a medium containing particles. This causes the light to deviate from its original path and makes the sky appear blue during the day. It is also responsible for the red and orange colors seen during sunrise and sunset.
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