Refraction of Light at
Plane Surfaces
Refraction, Laws of Refraction
and Refractive Index
Principle of Reversibility
of the path of light
Speed of Light in Different Media
Law of Refraction
Lateral Displacement
Refraction of Light
The change in the direction of the path of light when it passes from one transparent medium to another transparent medium obliquely is called refraction
- Rarer to Denser
- Denser to Rarer
- At Normal incidence
Cause of Refraction
bends towards the Normal
bends away from the Normal
Passes undeviated
the direction changes due to change of speed
in going from one medium to the other
frequency remains same
Incident ray, Refracted ray and Normal lie in the same plane
sin i / sin r = constant 1u2
wavelength(ƛ) = speed(V) / frequency(f)
u= c/V
1u2= Speed of light in medium 1/ Speed of light in medium 2
ƛ' = ƛ / u (frequency remains same)
Factors affecting the refractive index
Medium (speed of denser medium ↓ R.F ↑) ref: u= c/V
Temperature ↑ Speed(V) ↑ ∴ R.F ↓
Colour
speed- 🔴 > 🟣
R.F- 🟣 >🔴
Wavelength 🔴 > 🟣
2u1= 1/ 1u2
Difference between the emergent ray and the direction of incident ray
thickness of the medium
angle of incidence
Refractive index
PRISM
transparent medium bounded by 5 plane surfaces with a triangular cross section
Refraction of light
through a glass prism
𝜹 = (i1+i2) - (r1+r2)
r1 + r2= A
i1 + i2 = A + 𝜹
Factors affecting the angle of deviation
Material of prism-↑ R.F ↑ deviation
Angle of incidence ↑ deviation ↓
𝜹 min = 2i - A
↑ Angle of prism ↑ angle of deviation
Colour- 🟣 maximum 🔴 minimum
Wavelength ↑ angle of deviation ↓
REAL AND
APPARENT DEPTH
An object when placed in a denser medium when viewed from a rarer medium it appears to be at a depth less than the actual depth
Apparent depth = Real depth/ aUm
aUm= Real depth / Apparent depth
Shift = Real depth- Apparent depth
Shift = Real depth x ( 1- 1/ aUm)
Factors affecting the shift
R.F ↑ Shift ↑
Thickness of the medium ↑ Shift ↑
Wavelength ↑ Shift ↓
Colour 🟣 > 🔴
CRITICAL ANGLE AND
TOTAL INTERNAL REFLECTION
Denser medium to Rarer medium
i < C
i = C (refraction becomes 90°)
i > C (no refraction takes place)
Critical angle
Angle of incidence in the denser medium
to which the angle of refraction in the rarer
medium is 90°
Relationship between
Critical angle and R.F
Sin C= 1/ aUg
Factors affecting
Critical angle
Colour 🔴 max 🟣 min
Wavelength ↑ Critical angle ↑
Temperature ↑ Critical angle ↑
Total Internal Reflection
When a light travelling from a denser medium to a
rarer medium at an angle of incidence greater
than the critical angle then the ray is totally
reflected back into the denser medium
Conditions
Light must travel from denser to rarer medium only
Angle of Incidence must be greater to the Critical angle