L-7 | Light Reflection & Refraction Made Simple | REFRACTIVE INDEX MOST IMPORTANT TOPIC

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🌟 Light Reflection

Definition:
Reflection of light is the process by which light rays bounce back when they strike a smooth and shiny surface such as a mirror.

Key Points:

The incident ray is the incoming light ray that strikes the surface.

The reflected ray is the light ray that bounces off the surface.

The normal is an imaginary line perpendicular to the surface at the point of incidence.

Laws of Reflection:

The angle of incidence (i) is equal to the angle of reflection (r).

𝑖
=
𝑟
i=r

The incident ray, the reflected ray, and the normal all lie in the same plane.

Types of Reflection:

Regular (Specular) Reflection: Occurs on smooth surfaces; produces clear images (e.g., mirror).

Diffuse Reflection: Occurs on rough surfaces; scattered light, no clear image.

💧 Refractive Index

Definition:
The refractive index (or index of refraction) of a medium measures how much light slows down and bends (refracts) when entering that medium from another.

Refraction occurs when light passes from one transparent medium to another (e.g., air to water) and changes direction due to a change in speed.

Formula:

𝑛
=
𝑐
𝑣
n=
v
c
​


Where:

𝑛
n = refractive index

𝑐
c = speed of light in vacuum (≈
3
×
10
8
 
m/s
3×10
8
m/s)

𝑣
v = speed of light in the medium

Snell’s Law:
When light passes from one medium to another:

𝑛
1
sin
⁡
𝑖
=
𝑛
2
sin
⁡
𝑟
n
1
​

sini=n
2
​

sinr

Where:

𝑛
1
,
𝑛
2
n
1
​

,n
2
​

= refractive indices of the two media

𝑖
i = angle of incidence

𝑟
r = angle of refraction

Example:
When light passes from air (
𝑛
=
1.00
n=1.00) into water (
𝑛
≈
1.33
n≈1.33), it bends toward the normal because it slows down.

In summary:

Reflection → Light bounces off a surface.

Refraction & Refractive Index → Light bends when moving between materials of different optical densities, and the refractive index quantifies how much it slows down.