1. Ray travelling from rarer medium to denser medium
When a ray of light travels from a rarer medium (air) to a denser medium (glass or water), it bends towards the normal.
2. Ray striking surface at right angle
If a ray strikes the boundary perpendicular to the surface (angle of incidence = 0°), it passes straight without bending.
Answer: The ray travels in the same straight line.
3. Mathematical equation of Snell’s Law
Snell’s law states:
\[
n_1 \sin i = n_2 \sin r
\]
Where:
– \( n_1 \) = refractive index of first medium
– \( n_2 \) = refractive index of second medium
– \( i \) = angle of incidence
– \( r \) = angle of refraction
4. Speed of light in different media
Speed of light decreases as refractive index increases.
Order of refractive index:
Air < Water < Glass < Diamond
Therefore:
Highest speed: Water
Lowest speed: Diamond
5. Refraction through a glass slab
In a glass slab the emergent ray becomes parallel to the incident ray but shows a lateral displacement.
6. Value of \( n_{21} \times n_{12} \)
\[
n_{21} \times n_{12} = 1
\]
7. Angle of refraction when angle of incidence is 0°
If angle of incidence = 0°,
\[
r = 0^\circ
\]
The ray travels straight without bending.
