Ray Optics - 1 PPT Physics Class 12

 Page 1


RAY OPTICS - I
1. Refraction of Light 
2. Laws of Refraction
3. Principle of Reversibility of Light
4. Refraction through a Parallel Slab
5. Refraction through a Compound Slab
6. Apparent Depth of a Liquid
7. Total Internal Reflection
8. Refraction at Spherical Surfaces - Introduction
9. Assumptions and Sign Conventions
10.Refraction at Convex and Concave Surfaces
11.Lens Maker’s Formula
12.First and Second Principal Focus
13.Thin Lens Equation (Gaussian Form)
14.Linear Magnification
Page 2


RAY OPTICS - I
1. Refraction of Light 
2. Laws of Refraction
3. Principle of Reversibility of Light
4. Refraction through a Parallel Slab
5. Refraction through a Compound Slab
6. Apparent Depth of a Liquid
7. Total Internal Reflection
8. Refraction at Spherical Surfaces - Introduction
9. Assumptions and Sign Conventions
10.Refraction at Convex and Concave Surfaces
11.Lens Maker’s Formula
12.First and Second Principal Focus
13.Thin Lens Equation (Gaussian Form)
14.Linear Magnification
Refraction of Light:
Refraction is the phenomenon of change in the path of light as it travels 
from one medium to another (when the ray of light is incident obliquely).
It can also be defined as the phenomenon of change in speed of light 
from one medium to another.
Rarer
Rarer
Denser
N
N
r
i
r
i
Laws of Refraction:
I Law: The incident ray, the normal to 
the refracting surface at the point of 
incidence and the refracted ray all lie in 
the same plane.
II Law: For a given pair of media and for 
light of a given wavelength, the ratio of 
the sine of the angle of incidence to the 
sine of the angle of refraction is a 
constant. (Snell’s Law)
µ = 
sin i
sin r
(The constant µ is called refractive index of the medium,     
i is the angle of incidence and r is the angle of refraction.)
µ
Page 3


RAY OPTICS - I
1. Refraction of Light 
2. Laws of Refraction
3. Principle of Reversibility of Light
4. Refraction through a Parallel Slab
5. Refraction through a Compound Slab
6. Apparent Depth of a Liquid
7. Total Internal Reflection
8. Refraction at Spherical Surfaces - Introduction
9. Assumptions and Sign Conventions
10.Refraction at Convex and Concave Surfaces
11.Lens Maker’s Formula
12.First and Second Principal Focus
13.Thin Lens Equation (Gaussian Form)
14.Linear Magnification
Refraction of Light:
Refraction is the phenomenon of change in the path of light as it travels 
from one medium to another (when the ray of light is incident obliquely).
It can also be defined as the phenomenon of change in speed of light 
from one medium to another.
Rarer
Rarer
Denser
N
N
r
i
r
i
Laws of Refraction:
I Law: The incident ray, the normal to 
the refracting surface at the point of 
incidence and the refracted ray all lie in 
the same plane.
II Law: For a given pair of media and for 
light of a given wavelength, the ratio of 
the sine of the angle of incidence to the 
sine of the angle of refraction is a 
constant. (Snell’s Law)
µ = 
sin i
sin r
(The constant µ is called refractive index of the medium,     
i is the angle of incidence and r is the angle of refraction.)
µ
TIPS: 
1. µ of optically rarer medium is lower and that of a denser medium is higher.
2. µ of denser medium w.r.t. rarer medium is more than 1 and that of rarer 
medium w.r.t. denser medium is less than 1. (µ
air
= µ
vacuum
= 1)
3. In refraction, the velocity and wavelength of light change.
4. In refraction, the frequency and phase of light do not change.
5.
a
µ
m
= c
a
/ c
m        
and
a
µ
m
= ?
a
/ ?
m
Principle of Reversibility of Light:
Rarer   
(a)
N
r
i
Denser 
(b)
sin i
a
µ
b
= 
sin r
sin r
b
µ
a
= 
sin i
a
µ
b
x 
b
µ
a
= 1 or
a
µ
b
= 1 / 
b
µ
a
If a ray of light, after suffering any number of 
reflections and/or refractions has its path 
reversed at any stage, it travels back to the 
source along the same path in the opposite 
direction.
A natural consequence of the principle of reversibility is that the image and object 
positions can be interchanged.  These positions are called conjugate positions.
µ
Page 4


RAY OPTICS - I
1. Refraction of Light 
2. Laws of Refraction
3. Principle of Reversibility of Light
4. Refraction through a Parallel Slab
5. Refraction through a Compound Slab
6. Apparent Depth of a Liquid
7. Total Internal Reflection
8. Refraction at Spherical Surfaces - Introduction
9. Assumptions and Sign Conventions
10.Refraction at Convex and Concave Surfaces
11.Lens Maker’s Formula
12.First and Second Principal Focus
13.Thin Lens Equation (Gaussian Form)
14.Linear Magnification
Refraction of Light:
Refraction is the phenomenon of change in the path of light as it travels 
from one medium to another (when the ray of light is incident obliquely).
It can also be defined as the phenomenon of change in speed of light 
from one medium to another.
Rarer
Rarer
Denser
N
N
r
i
r
i
Laws of Refraction:
I Law: The incident ray, the normal to 
the refracting surface at the point of 
incidence and the refracted ray all lie in 
the same plane.
II Law: For a given pair of media and for 
light of a given wavelength, the ratio of 
the sine of the angle of incidence to the 
sine of the angle of refraction is a 
constant. (Snell’s Law)
µ = 
sin i
sin r
(The constant µ is called refractive index of the medium,     
i is the angle of incidence and r is the angle of refraction.)
µ
TIPS: 
1. µ of optically rarer medium is lower and that of a denser medium is higher.
2. µ of denser medium w.r.t. rarer medium is more than 1 and that of rarer 
medium w.r.t. denser medium is less than 1. (µ
air
= µ
vacuum
= 1)
3. In refraction, the velocity and wavelength of light change.
4. In refraction, the frequency and phase of light do not change.
5.
a
µ
m
= c
a
/ c
m        
and
a
µ
m
= ?
a
/ ?
m
Principle of Reversibility of Light:
Rarer   
(a)
N
r
i
Denser 
(b)
sin i
a
µ
b
= 
sin r
sin r
b
µ
a
= 
sin i
a
µ
b
x 
b
µ
a
= 1 or
a
µ
b
= 1 / 
b
µ
a
If a ray of light, after suffering any number of 
reflections and/or refractions has its path 
reversed at any stage, it travels back to the 
source along the same path in the opposite 
direction.
A natural consequence of the principle of reversibility is that the image and object 
positions can be interchanged.  These positions are called conjugate positions.
µ
Refraction through a Parallel Slab:
Rarer (a)
Rarer (a)
Denser 
(b)
N
N
r
1
i
1
i
2
r
2
M
t
d
y
sin i
1
a
µ
b
= 
sin r
1
sin i
2
b
µ
a
= 
sin r
2
But
a
µ
b
x 
b
µ
a
= 1
sin i
1
sin r
1
sin i
2
sin r
2
x
= 1
It implies that i
1 
= r
2 
and i
2
= r
1
since i
1
? r
1
and i
2
? r
2
.
Lateral Shift: 
t sin d
y = 
cos r
1
t sin(i
1
- r
1
)
y = 
cos r
1
or
Special Case:
If i
1
is very small, then r
1
is also very small.                                             
i.e. sin(i
1
– r
1
) = i
1
– r
1
and cos r
1
= 1
y = t (i
1
– r
1
) 
or
y = t i
1
(1 – 1 /
a
µ
b
) 
µ
Page 5


RAY OPTICS - I
1. Refraction of Light 
2. Laws of Refraction
3. Principle of Reversibility of Light
4. Refraction through a Parallel Slab
5. Refraction through a Compound Slab
6. Apparent Depth of a Liquid
7. Total Internal Reflection
8. Refraction at Spherical Surfaces - Introduction
9. Assumptions and Sign Conventions
10.Refraction at Convex and Concave Surfaces
11.Lens Maker’s Formula
12.First and Second Principal Focus
13.Thin Lens Equation (Gaussian Form)
14.Linear Magnification
Refraction of Light:
Refraction is the phenomenon of change in the path of light as it travels 
from one medium to another (when the ray of light is incident obliquely).
It can also be defined as the phenomenon of change in speed of light 
from one medium to another.
Rarer
Rarer
Denser
N
N
r
i
r
i
Laws of Refraction:
I Law: The incident ray, the normal to 
the refracting surface at the point of 
incidence and the refracted ray all lie in 
the same plane.
II Law: For a given pair of media and for 
light of a given wavelength, the ratio of 
the sine of the angle of incidence to the 
sine of the angle of refraction is a 
constant. (Snell’s Law)
µ = 
sin i
sin r
(The constant µ is called refractive index of the medium,     
i is the angle of incidence and r is the angle of refraction.)
µ
TIPS: 
1. µ of optically rarer medium is lower and that of a denser medium is higher.
2. µ of denser medium w.r.t. rarer medium is more than 1 and that of rarer 
medium w.r.t. denser medium is less than 1. (µ
air
= µ
vacuum
= 1)
3. In refraction, the velocity and wavelength of light change.
4. In refraction, the frequency and phase of light do not change.
5.
a
µ
m
= c
a
/ c
m        
and
a
µ
m
= ?
a
/ ?
m
Principle of Reversibility of Light:
Rarer   
(a)
N
r
i
Denser 
(b)
sin i
a
µ
b
= 
sin r
sin r
b
µ
a
= 
sin i
a
µ
b
x 
b
µ
a
= 1 or
a
µ
b
= 1 / 
b
µ
a
If a ray of light, after suffering any number of 
reflections and/or refractions has its path 
reversed at any stage, it travels back to the 
source along the same path in the opposite 
direction.
A natural consequence of the principle of reversibility is that the image and object 
positions can be interchanged.  These positions are called conjugate positions.
µ
Refraction through a Parallel Slab:
Rarer (a)
Rarer (a)
Denser 
(b)
N
N
r
1
i
1
i
2
r
2
M
t
d
y
sin i
1
a
µ
b
= 
sin r
1
sin i
2
b
µ
a
= 
sin r
2
But
a
µ
b
x 
b
µ
a
= 1
sin i
1
sin r
1
sin i
2
sin r
2
x
= 1
It implies that i
1 
= r
2 
and i
2
= r
1
since i
1
? r
1
and i
2
? r
2
.
Lateral Shift: 
t sin d
y = 
cos r
1
t sin(i
1
- r
1
)
y = 
cos r
1
or
Special Case:
If i
1
is very small, then r
1
is also very small.                                             
i.e. sin(i
1
– r
1
) = i
1
– r
1
and cos r
1
= 1
y = t (i
1
– r
1
) 
or
y = t i
1
(1 – 1 /
a
µ
b
) 
µ
Refraction through a Compound Slab:
Rarer (a)
Rarer (a)
Denser 
(b)
N
N
µ
b
r
1
i
1
r
1
r
2
r
2
i
1
Denser 
(c)
µ
c
N
sin i
1
a
µ
b
= 
sin r
1
sin r
1
b
µ
c
= 
sin r
2
a
µ
b
x 
b
µ
c
x 
c
µ
a
= 1
sin r
2
c
µ
a
= 
sin i
1
a
µ
b
x 
b
µ
c
= 
a
µ
c
or
b
µ
c
= 
a
µ
c 
/
a
µ
b
or
µ
a
µ
c 
> µ
b