This document provides information about reflection and refraction of light, including: 1) The laws of reflection and refraction, such as the fact that the angle of incidence equals the angle of reflection, and Snell's law relating the sines of the angles of incidence and refraction to the refractive indices. 2) Concepts like relative and absolute refractive index, how refractive index depends on wavelength, limitations of Snell's law. 3) Examples of refraction like mirages and applications like periscopes and binoculars. 4) Total internal reflection and the conditions required for it to occur. 5) Dispersion of light through a prism and why white light separates

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2. By:- Prof. Dnyanesh Vaidya

3. Reflection of light.
 When light rays fall on any opaque
surface (like plane mirror), they are
returned back on the same side of the
surface. This phenomenon is called
reflection of light.

4. Laws of Reflection:-
1. The angle of incidence and angle of refraction
are of equal measures.
i.e.
2. Incident ray, reflected ray and the normal at the
point of incidence lie in the same plane.
3. Incident ray and reflected ray are on the opposite
sides of the normal at the point of incidence.
m i m r

5. Refraction of light.
“the bending of a ray of light when it travels
from one transparent medium to another,
having different optical density is called
refraction of light.”

8. Laws of Refraction :
Snell’s law
1
2
sin
.
sin
sin
sin
i
const
r
i
r
C
C

9. Snell

10. Relative Refractive Index and
Absolute Refractive Index
1 2
2
sin
Relative Refractive Index
sin
sin
Absolute Refractive Index
sin
a
i
r
i
r

11. 1
1
2
2
2 2 1
1 1 2
1
1 2
2
2
1 2
1
c
C
c
C
c C C
c C C
C
But
C

12. Refractive index in terms of
wavelength
1
1 2
2
1
1 2
2
1
1 2
2
C
C
But C f
f
f

13. Limitation of Snell’s Law

14. Practical examples of refraction of
light

16. Numericals
If the refraction indices of glass and water is 1.5
and 1.33 respectively calculate the velocity of
light in glass and water.

17. Ans: Ca = 3 × 108 m/s
ng = 1.5 ,
cg = ? , cw = ?
w
4
n 1.33
3
a
g
g
8
a
g
g
8
g
c
n
c
c 3 10
c
n 1.5
c 2 10 m / s

18. a
w
w
8 8
a
w
w
c
n
c
c 3 10 3 3 10
c
4n 4
3
8
wc 2.25 10 m / s

19. Total Internal Reflection :-

20. Necessary conditions for
total internal reflection
1. The ray of light must travel from optically
denser medium to optically rarer medium.
2. The angle of incidence in the denser
medium must be greater than the critical
angle for that pair.

21. Thus, refractive index of rarer medium (air)
with respect to the denser medium (water)
is: sin
sin90
sin90 1
sin
1 1
sin
d r
d r
r d
d r
c
But
c
c

22. Mirage: -

25. Periscope

26. Binacular

31. Why diamond will shine?

32. For Home works
1. If the refractive indices of diamond and glass
are 2.4 and 1.5 respectively. Compare the
velocity of light in diamond and glass.
2. The R.I of water relative to air is 4/3. A ray of
light passing through water into air is incident
at interface at an angle of 35° with the normal.
What angle does the refracted ray make with
the normal?

33. Prizm

36.  ∠δ = ∠EQR + ∠ERQ .(exterior angles property)
= (i – r1) + (e – r2)
∠δ = (i + e) – (r1 + r2) ………(1)
 From ΔQDR,
r1 + r2 + D = 180° ………(2)
 from □AQDR,
□ AQDR is a cyclic quadrilateral
∵ ∠Q = ∠R = 90°
∴ ∠A + ∠D = 180° ……..(3)

37.  From (2) and (3)
r1 + r2 + D = A + D
∴ r1 + r2 = A
 Substituting A in equation (1),
δ = (i + e) – A …….(4)
 i.e. A + δ = (i + e) ……(5)

39.  Thus, i = e.
∴ δ = δm
 ∴ Equation (5) will become
A + δm = (i + i)
A + δm = 2i
 ………(6)A m
i
2

40.  As i = e then r1 = r2 = r (say)
 Substituting this value in equation of A,
 r + r = A
 2r = A
 ……..(7)A
r
2

41.  Substituting equations (6) + (7) in
formula of refractive index,

sin i
sin r
A m
sin
2
sin A / 2

42. Thin Prism
 (A < 6°).
 sin θ = θ. m
m
m
m
m
A m
sin
2
sin A / 2
A
2
A
2
A
=
A
A A
A A
A 1

43. Dispersion of light

44. Dispersion of white light takes
place because :
 1. White light is composed of seven different
colours.
 2. Velocities and refractive indices
 3. After emerging out from the prism, different
colours travel in different directions. Hence,
they remain separated.

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