Light is an essential part of our daily life. It helps us see objects around us and is fundamental to many natural phenomena. In this chapter, we learn about the nature of light, reflection, refraction, and how we see objects.
1. What is Light?
- Light is a form of energy that makes things visible.
- It travels in a straight line in a medium (like air).
- Sources of light:
- Natural: Sun, stars, firefly, etc.
- Artificial: Bulbs, torches, candles, lamps.
2. How Light Travels
- Rectilinear Propagation: Light travels in a straight line.
- Shadow Formation: When an opaque object blocks light, it forms a shadow.
- Experiments:
- Using a pinhole and a torch to show light travels in straight lines.
- Formation of shadows with hands or objects.
3. Reflection of Light
- Reflection: Bouncing back of light from a surface.
- Laws of Reflection:
- Angle of incidence = Angle of reflection
- Incident ray, reflected ray, and normal lie in the same plane
- Types of Surfaces:
- Plane Mirror: Produces a virtual image (upright and same size).
- Spherical Mirrors: Concave and convex mirrors used in torches, shaving mirrors, vehicles, etc.
4. Image Formation by Plane Mirrors
- Characteristics of Image:
- Virtual and upright
- Same size as the object
- Laterally inverted (left appears right, right appears left)
5. Refraction of Light
- Refraction: Bending of light when it passes from one medium to another.
- Examples: Pencil in water appears bent, spoon in a glass of water.
- Laws of Refraction:
- Incident ray, refracted ray, and normal lie in the same plane.
- Light bends towards the normal in denser medium and away in rarer medium.
6. Lenses
- Convex Lens (Converging Lens): Brings light rays together. Used in magnifying glasses, cameras, and eyes.
- Concave Lens (Diverging Lens): Spreads light rays apart. Used in spectacles for myopia.
7. Dispersion of Light
- White light can split into seven colors (VIBGYOR) using a prism.
- Rainbows are natural examples of dispersion of sunlight by water droplets.
8. Human Eye
- Parts of Eye: Cornea, Lens, Retina, Iris, Optic nerve.
- Function of Lens: Focuses light on the retina.
- Defects of Vision:
- Myopia (Nearsightedness): Corrected with concave lens.
- Hypermetropia (Farsightedness): Corrected with convex lens.
9. Uses of Light
- Essential for vision.
- Used in communication (fiber optics).
- Used in medical tools (microscopes, lasers).
Important One-Word / Very Short Answers for Exams
- Form of energy – Light
- Source of natural light – Sun
- Source of artificial light – Bulb
- Light travels in – Straight line
- Device showing light path – Ray box
- Path of light – Ray
- Point from which light spreads – Source
- Reflection of light – Reflection
- Surface producing reflection – Mirror
- Smooth reflecting surface – Plane mirror
- Curved mirror – Concave
- Curved mirror – Convex
- Reflection from plane mirror – Regular
- Reflection from rough surface – Diffused
- Image formed by plane mirror – Virtual
- Mirror producing real image – Concave
- Mirror producing virtual image – Convex
- Bending of light – Refraction
- Medium where light slows down – Denser
- Medium where light speeds up – Rarer
- Lens bending light inward – Convex
- Lens bending light outward – Concave
- Converging lens – Convex
- Diverging lens – Concave
- Focal point of lens – Focus
- Focal length – Distance
- Splitting of light – Dispersion
- Band of colors – Spectrum
- Light color with shortest wavelength – Violet
- Light color with longest wavelength – Red
- Reflection from water surface – Specular
- Rainbow formation – Refraction
- Tyndall effect – Scattering
- Shadow – Shadow
- Umbra of shadow – Dark
- Penumbra of shadow – Partial
- Lens used in spectacles for farsightedness – Convex
- Lens used in spectacles for nearsightedness – Concave
- Mirror used in vehicles – Convex
- Mirror used in headlights – Concave