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1. Defects of Vision
- Myopia (Near-sightedness): Can see nearby objects clearly but distant objects appear blurred. The image forms in front of the retina. Corrected using a Concave Lens.
- Hypermetropia (Far-sightedness): Can see distant objects clearly but nearby objects appear blurred. The image forms behind the retina. Corrected using a Convex Lens.
- Presbyopia: Common in old age due to weakening of ciliary muscles. Corrected using Bifocal Lenses.
2. Refraction through a Prism
When white light passes through a glass prism, it splits into its seven constituent colors (VIBGYOR). This phenomenon is called Dispersion. Violet light bends the most, and red light bends the least.
3. Atmospheric Refraction Phenomena
- Twinkling of Stars: Due to the bending of starlight by the varying refractive indices of different atmospheric layers.
- Advanced Sunrise & Delayed Sunset: The sun appears 2 minutes early and 2 minutes late due to atmospheric refraction.
- Tyndall Effect: Scattering of light by particles in a colloid or fine suspension (e.g., light through a dusty room or dense canopy).
CBSE Board Exam Classic Question
Why is the sky blue? The molecules of air and other fine particles in the atmosphere are smaller in size than the wavelength of visible light. These particles scatter shorter wavelengths (blue) more strongly than longer wavelengths (red). This scattered blue light enters our eyes, making the sky appear blue.