LIGHT & OPTICS

🌟 1. Nature of Light

📘 What is Light?

Light is a form of electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight. It behaves both like a wave and a particle — a concept known as wave-particle duality.

🔍 Scientific Definition:

Light is made up of photons — massless particles that travel in a wave-like pattern. These photons carry energy and travel at a constant speed in a vacuum:
Speed of light (c) = 3 × 10⁸ m/s

🌊 Wave Nature of Light

🧬 Particle Nature of Light (Photon)

• Photon is a particle of light energy.
• Energy of a photon:
  E = h × f
  Where h = Planck’s constant and f = frequency of light

🔦 Example:

In the photoelectric effect, light shining on a metal surface causes electrons to be ejected. This effect proves that light acts as particles, not just waves.

🔁 2. Reflection

📘 What is Reflection?

Reflection is the bouncing back of light when it hits a surface that it cannot pass through. This is how we see objects—they reflect light into our eyes.

🔍 Laws of Reflection:

1. Angle of incidence = Angle of reflection
2. Incident ray, reflected ray, and normal all lie in the same plane

🪞Types of Reflection

🧠 Real-Life Examples:

• Bathroom mirror: Shows a clear image through regular reflection.
• Moonlight: The moon doesn’t emit its own light; it reflects sunlight.
• Road reflectors: Help drivers see at night by reflecting car headlights.

🔎 Diagram (Text Description):

• A straight line (the normal) is perpendicular to a surface.
• An incident ray strikes the surface at angle θᵢ.
• A reflected ray leaves the surface at angle θᵣ = θᵢ.
• All rays lie in the same plane.

🔄 3. Refraction

📘 What is Refraction?

Refraction is the bending of light as it passes from one transparent medium to another (e.g., from air to water), due to a change in speed.

🔍 Why Refraction Happens:

• Light slows down or speeds up depending on the density of the medium.
• It bends toward the normal when entering a denser medium.
• It bends away from the normal when entering a less dense medium.

📐 Snell’s Law (Law of Refraction)

n₁ × sin(θ₁) = n₂ × sin(θ₂)
Where:

• n₁, n₂: Refractive indices of the two media
• θ₁: Angle of incidence
• θ₂: Angle of refraction

🧠 Real-Life Examples:

• A straw in water appears bent or broken.
• Lenses in spectacles refract light to focus it correctly on the retina.
• Rainbow: Sunlight refracts through raindrops, separating into colors.

🔎 Diagram (Text Description):

• Light ray enters water from air.
• It bends toward the normal due to higher density.
• The outgoing ray changes direction based on refractive index.

🔍 4. Lenses

📘 What is a Lens?

A lens is a transparent optical device that refracts light rays to converge or diverge them, helping form images.

🔍 Types of Lenses

🧠 Properties of Lenses:

• Principal axis: The central line passing through the lens.
• Focal point (F): Point where light rays meet (convex) or appear to diverge from (concave).
• Focal length (f): Distance from lens center to focal point.

🧠 Real-Life Examples:

• Microscopes: Use multiple convex lenses to magnify tiny objects.
• Projectors: Use convex lenses to enlarge images on a screen.
• Eyeglasses: Concave lenses for myopia, convex lenses for hyperopia.
• Cameras: Adjustable convex lenses focus light to form clear images.

📦 More Optical Phenomena

🌍 Applications of Light & Optics

📌 Summary Table