1.Reflection of Light
➤ What is Reflection?
Reflection is when light bounces back from a smooth or shiny surface, like a mirror.
Example: When you look in a mirror, your face appears due to reflection.➤ Laws of Reflection
- Angle of incidence = Angle of reflection
- Incident ray, reflected ray, and normal (a line perpendicular to the surface at the point of incidence) all lie in the same plane.
➤ What is Refraction?
Refraction is the bending of light when it passes from one medium to another (e.g., air to water), due to a change in speed.
Example: A pencil looks bent when placed in a glass of water.➤ Laws of Refraction:
- The incident ray, refracted ray, and normal all lie in the same plane.
- Snell’s Law:
- i = angle of incidence
- r = angle of refraction
- n = refractive index
It tells how much light slows down in a medium.
- c = speed of light in vacuum
- v = speed of light in medium
➤ What happens when light travels from denser to rarer medium (like water to air)?
- It bends away from the normal (refraction).
- At a certain angle, called the critical angle, the refracted ray grazes along the surface.
- If the angle of incidence exceeds the critical angle, light is completely reflected back inside — this is called:
Conditions for TIR:
- Light must travel from denser to rarer medium.
- Angle of incidence > critical angle
Example: Fiber Optic Cables
- Light enters the glass core (denser medium) and hits the boundary at an angle > critical angle.
- It undergoes Total Internal Reflection, and keeps bouncing inside, carrying the signal efficiently over long distances.
Uses:
- Internet/data transfer (fiber optics)
- Endoscopes in medical fields
- Periscopes