💡 1. Properties of Light
- Light is a form of electromagnetic energy (can travel through vacuum)
- Light travels in straight lines (rectilinear propagation) — proven by shadows,
pinhole camera
- Speed of light in vacuum = 3 × 10⁸ m/s (about 300,000 km per second — fastest speed
in the universe!)
- Light can be reflected, refracted, and absorbed
- White light is made up of 7 colours (VIBGYOR): Violet, Indigo, Blue, Green, Yellow,
Orange, Red
🪞 2. Reflection of Light
When light hits a smooth, shiny surface and bounces back, this is called reflection.
Laws of Reflection:
1️⃣ The angle of incidence (∠i) = angle of reflection (∠r)
2️⃣ The incident ray, reflected ray, and normal at the point of incidence all lie in the same
plane
Both laws always hold true — on any reflecting surface (mirror, water, metal, etc.)!
📸 AI Image Prompt
A clear, labeled educational diagram showing the laws of reflection. On the left
side: a bright yellow arrow (incoming "Incident Ray") hits the center of a flat horizontal mirror at an
angle. At the point of contact, a vertical dotted blue line goes straight up (labeled "Normal —
perpendicular to mirror surface"). The angle between the incident ray and the Normal is labeled "Angle
of Incidence (i)" with a curved arc in yellow. A red reflected ray bounces off symmetrically on the
other side of the Normal. The angle between the reflected ray and the Normal is labeled "Angle of
Reflection (r)" with a red arc. A bold equation is shown: "∠i = ∠r". Below the mirror surface, a
reflection of the incident ray geometry is shown (the region inside mirror is shaded light grey). All
labels are bold, black on white background. Additional text below: "Both incident ray, normal, and
reflected ray lie in the same plane." Clean physics diagram style.
Fig. 11.1 — Laws of reflection of light
🪞 3. Plane Mirror — Image Properties
When you look into a
plane mirror, the image you see is:
- 📏 Same size as the object
- 📍 Same distance behind mirror as object is in front
- 🔨 Virtual (cannot be projected on a screen)
- ⬅️➡️ Laterally inverted (left-right reversed — AMBULANCE written in mirror
writing!)
- ↕️ Erect (not upside down)
🌈 4. Types of Mirrors and Lenses
|
Concave Mirror |
Convex Mirror |
Convex Lens |
Concave Lens |
| Shape |
Curves inward (like inside of a spoon) |
Curves outward (like back of spoon) |
Thicker in middle |
Thinner in middle |
| Effect on light |
Converges (brings rays together) — converging mirror |
Diverges (spreads rays apart) — diverging mirror |
Converges rays to a focal point |
Diverges rays — appears to spread out from a point |
| Image type |
Real & inverted (when object beyond focus) OR Virtual & erect (when object within focus)
|
Always Virtual, Erect, Diminished (smaller) |
Real & inverted (object beyond focus); Virtual, erect, magnified (within focus) |
Always Virtual, Erect, Diminished |
| Uses |
Shaving/makeup mirror, reflecting telescopes, torch/headlamps, solar cookers, dentist's mirror |
Rear view mirrors in vehicles (wide field of view) |
Magnifying glass, eye lens (camera/eye), projectors |
Spectacles for short-sighted (myopia), camera viewfinders |
🌈 5. Dispersion of Light — The Rainbow!
White light enters glass prism
⬇
Light bends (refracts) as it enters denser glass
⬇
Different colours bend by different amounts (violet
bends most, red bends least)
⬇
White light splits into VIBGYOR spectrum 🌈
The same happens in the sky when sunlight passes through raindrops → Rainbow!
Violet, Indigo, Blue, Green,
Yellow, Orange, Red
Remember: "Vibgyor" or mnemonic "Vibgyor is the rainbow's order"
Rainbow forms when: Sunlight → enters raindrop → refracts → internally reflects → refracts again on exit →
dispersion visible
👁️ 6. Structure of the Human Eye
| Part |
Function |
| Cornea |
Transparent protective layer; does most of the light bending (refraction) |
| Iris |
Coloured part; controls the size of pupil (adjusts amount of light entering) |
| Pupil |
The dark circular opening in the centre of iris; lets light in |
| Lens (Crystalline) |
Flexible convex lens; adjusts focus for near and far objects (Accommodation)
|
| Retina |
Light-sensitive screen at back of eye; contains rods (B&W) and cones (colour vision). Image
forms here (inverted & real) |
| Optic nerve |
Sends signals from retina to brain; brain interprets image right-side up |
📝 7. Quick Revision
- Light travels in straight lines (rectilinear propagation). Speed = 3 × 10⁸ m/s
- Laws of Reflection: ∠i = ∠r; all three (incident ray, normal, reflected ray) lie in
same plane
- Plane mirror image: same size, virtual, erect, laterally inverted, same distance behind mirror
- Concave mirror: converging → uses: torch, dentist, solar cooker. Convex
mirror: diverging → rear-view mirror
- Convex lens: converging → magnifying glass, camera, eye. Concave
lens: diverging → spectacles for myopia
- Dispersion: white light splits into 7 colours through prism. VIBGYOR (Violet bends
most, Red bends least)
- Rainbow = dispersion of sunlight by raindrops
- Eye: Cornea → Pupil (controlled by Iris) → Lens → Retina (image forms) → Optic nerve → Brain
