Chapter "Light – Reflection and Refraction": NOTES
1. Introduction to Light:
- Light is a form of energy that allows us to see objects around us.
- It travels in straight lines called rays.
2. Reflection of Light:
- Reflection is when light bounces off a surface.
- Laws of reflection:
- The angle of incidence is equal to the angle of reflection.
- Incident ray, reflected ray, and the normal (perpendicular line) to the surface at the point of incidence all lie in the same plane.
- Examples: mirrors, polished surfaces.
3. Image Formation by a Plane Mirror:
- Virtual image: formed behind the mirror, appears upright and of the same size as the object.
- Characteristics of image formed by a plane mirror:
- Virtual
- Upright
- Same size as the object
- Laterally inverted (left-right reversed)
4. Spherical Mirrors:
- Concave mirror:
- Converging mirror (brings parallel rays to a focus).
- Forms real or virtual images depending on the position of the object.
- Convex mirror:
- Diverging mirror (spreads out parallel rays).
- Always forms virtual, erect, and diminished images.
5. Image Formation by Spherical Mirrors:
- Ray diagrams: Used to locate images formed by spherical mirrors.
- Principal focus, focal length, and mirror equation.
6. Refraction of Light:
- Refraction is the bending of light when it passes from one transparent medium to another.
- Refractive index: Ratio of the speed of light in vacuum to its speed in the medium.
- Laws of refraction:
- The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane.
- Snell's law: \( \frac{\sin i}{\sin r} = \frac{n_2}{n_1} \), where \( n_1 \) and \( n_2 \) are refractive indices of the two media.
7. Refraction by Spherical Lenses:
- Convex lens:
- Converging lens (brings parallel rays to a focus).
- Forms real or virtual, inverted or upright images.
- Concave lens:
- Diverging lens (spreads out parallel rays).
- Always forms virtual, erect, and diminished images.
8. Image Formation by Lenses:
- Ray diagrams: Used to locate images formed by lenses.
- Principal focus, focal length, lens formula.
9. Power of a Lens:
- Power \( P \) of a lens in dioptres (D): \( P = \frac{1}{f} \), where \( f \) is the focal length in meters.
10. Human Eye:
- Structure and functions of the human eye.
- Defects of vision (myopia, hyperopia, presbyopia) and their corrections (using lenses).
11. Optical Instruments:
- Simple microscope, compound microscope, astronomical telescope.
- Construction and working principles.
12. Atmospheric Refraction:
- Causes the apparent bending of light rays when they pass through the Earth's atmosphere.
- Results in phenomena like sunrise, sunset, and twinkling of stars.
13. Dispersion of Light:
- Splitting of white light into its constituent colors (spectrum) due to different wavelengths.
- Prism and rainbow formation.
14. Scattering of Light:
- Explanation of why the sky appears blue and sunsets appear red.
- Rayleigh scattering and its effects.
These are the key points covered in the chapter on "Light – Reflection and Refraction". Understanding these concepts will help in grasping how light behaves and how we perceive objects through it.