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8/14/2019 wu1c3 by Adel Khamis
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Unit one-1-Chapter Three
Light as wave motion
Light:
Light is a branch of
waves.
It consists of .. field and
field perpendicular to each other and
. to the direction of
propagation, therefore it
considers as (longitudinal
transverse) waves, and it
(required / not required)
medium to propagate.
Propagation of light:
Light propagates in
..
Reflection of light:
Definition. :
The laws of reflection:
..
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Unit one-2-Chapter Three
Refraction of light:
D
efiniti
on:
If the angle of incident is zero, the ray fall (normal /
perpendicular) to the surface, it
..
G.R:.
When the ray incident with angle equal zero it
suffers no refraction.
..
..
The optical piece used in the experiment is semi
circular prism, and the light beam fall on the plane
surface.
..
..
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Unit one-3-Chapter Three
The laws of refraction:
First Law states:
Second law states:
Refractive index (n:)
Definition :
.
G.R:
The value of refractive index is greater than one.
.
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v
cn =
V
C
sin
sin(n)indexrefractive ==
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...........
..........21=n
..........
..........=
............
...........=
..........
..........21=n
Unit one-4-Chapter Three
Relative refractive index (1n2:)
Definition.. :
F
actors affected on relative refractive index
.. ,..
Factor affected on absolute refractive index
..
Relation between relative and absolute index:
* The first medium(1) has velocity of
light = V1
* The secondmedium (2) hasvelocity of light =
V2
* The first medium(air) has velocity
of light = C
* The second
medium (1) hasvelocity of light =V1
* The first medium(air) has velocity
of light = C
* The second
medium (2) hasvelocity of light =V2
C = x.. C = . x.
n V = n V
.......
.......
.......
.......
.......
.......21 ===n
Work Sheet2008/2009
==sin
sin
2v
1vn
21
..........
..........
2
1 =V
V
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Unit one-5-Chapter Three
The angle of incidence in a medium is 60 and the
angle of refraction in the other medium is 30, the
relative refractive index from the first to the second
medium is .. and that from the
second to the first is..
Refractive index of air =
.
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Unit one-6-Chapter Three
Snells law:
*
)1(.........
........21 =n
(related to absolute refractive index).
*
)2(...........
.........21 =n
(related to velocity)
From (1) and (2)
*
)3(.............
............
1
2 =n
n
*
)4(sin
sin
2
1
V
Vbut =
From (3) and (4)
Prove that:
12
21n
1n =
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.......sin........sin21nn =
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Unit one-7-Chapter Three
N.B:
The medium, which has less velocity, considered
optically (denser/ less dense) than the medium,which has great velocity.
What is meant by:
The absolute refractive index of glass = 1.5
..
Give reason for:
Light passing into a denser medium is bent toward
the normal.
..
Light passing into less denser medium is bent away
from the normal.
..
You can see your image at window glass nightly,
while you cant see it at day time.
..
Examples:
Given that the velocity of light in air = 3x108 m/s
and that in water equal 2x108 m/s, if a light ray fall
with angle of 30 with water surface, find the angle
between refracted ray and reflected ray.
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Unit one-8-Chapter Three
[8445]
A light ray falls on the surface of glass of absolute
refractive index 1.5 with angle of incidence that is
equal to 30. Find the angle of refraction.
[19.47]
Given that the absolute refractive index for water is
4/3 and that for glass is 3/2 find:
a) The relative refractive index from water to glass.
b) The relative refractive index from glass to water.
[9/8,8/9]
An incident ray by an angle 48.5 on one face of a
glass rectangular block (n = 1.5) the angle of
refraction is and the angle of
emerge is
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Unit one-9-Chapter Three
Give reason:
When white light refract, it
separated into seven colors.
Interference of light (young experiment:)
Explain an experiment to illustrate the interference of
light by using of double slit:
.
..
..
.
Where:
y.. =
d =
R =
=
N.B:.
1meter (m) = Angstrom (.)
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d
Ry =
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Unit one-10-Chapter Three
Give reason for:
Monochromatic light is used in Youngs experiment.
The fringes become clear when the distance
between two slits become small.
.
Red light is preferred to violet in young experiment.
.
In youngs experiment when a red light of
frequency 1x1015 Hz is used the distance between
the fringes was 2 mm. Calculate the distance when
violet light of frequency 0.6x1015 Hz is used.
.
.
.
[3.3x10-3m]
What is the benefit of double slit in young
experiment.
Diffraction of light:
Definition :
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Unit one-11-Chapter Three
The aperture or the slit must be (equal or
less than / larger than) the wavelength of the
light.
If the aperture has circular shape
the diffraction appear at the screen
as airys disk, where it consists of
. at the middle followed
by rings.
If the aperture has rectangular
shape the diffraction appear as
Give reason:
Sound waves diffract at edges of the doors and windows but light
not.
.
Question:
What do you know about Airys disk
.
.Light as wave motion:
Light considers as wave motion because:
.
.
.
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Unit one-12-Chapter Three
.
.
Critical angle and total reflection:
When a ray of light passes
from a denser optical medium
to a less dense medium, it
refracts . the
normal.
By increasing of the incident angle, the refracted
angle will (increase/ decrease) to reach ..
By increasing of the incident angle, the emerge ray
will return at the same medium forming
...
Critical angle:
Definition. :
If the incident angle is smaller than the critical
angle the ray will .; while it will
if the angle of incident is greater than the
critical angle.
Find the relation between the critical angleand the absolute reflective index:
Prove that:
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csin
1n
=
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Unit one-13-Chapter Three
If the critical angle for a medium to air is 45 then
the absolute refractive index is..
[1.4]
N.B:
anm=
csin
1n
=
mna=
c21 sinn =
Totally reflection:
Definition
G.R:.
The totally reflection is preferred than the normalreflection.
Factors required for total reflection:
If the critical angle of water is 45 and for glass =
40. Find the relative refracted index between glass
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Unit one-14-Chapter Three
and water. And find the critical angle of light from
glass to water.
[0.90903,6522]
Calculate the critical angle between glass and
water given that their refractive indexes are 1.6
and 1.33 respectively.
[5613]
N.b:.
From less dens medium to dens medium:
If = 0 then
(G.R)
.
If > 0 then
From dens medium to less dens medium:
If = 0 then
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Unit one-15-Chapter Three
Ifc > > 0 then
If = c then ...,=
If > c then
Application of totally reflection:
Fiber optics (Optical fibers:)
It is a fine hollow fiber of a
transparent material has (small/
high) critical angle.
When the incident ray enters, it falls at the surface
with an angle greater than the critical angle,
therefore the ray will..
Then the ray will emerge from the other end of the
fiber.
It is widely used as . in medicine and
.. in communications.
Mirage:
Definition. :
..
..
The layer of air with contact to the
earth surface (high / low) in temperature and
became (dens / less dens)
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Unit one-16-Chapter Three
The upper layer will be (denser / less dens) than
the lower layer.
The ray falls from the object will refract many timethrough the layer of hot air (increasing/ decreasing)
of its angle.
When the angle of incident becomes (greater/
smaller) than the critical angle the ray will
. forming.
Totally reflected prism:
It is used to change the path of light rays either by 90 or 180.
Draw a diagram to change the path of light ray by
180. Which used in..
Draw a diagram for binoculars.
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Unit one-17-Chapter Three
Draw a diagram to change the path of light ray by
90. Which used in..
Give reason:
The reflected prism is preferred to metallic mirrors.
..
..
Reflected prism is painted with cryolite (reflected
layer.)
..
..
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1A212123
Unit one-18-Chapter Three
Deviat
ion
with a
triang
ular
prism:
From the
previous
diagram:
A + 3=
..
1 + 2
+ 3 =
.
A =
.. + .(1)
= + .(2)
1 - =(3)
2 - =(4)
From (2) and (3) & (4)
- + . - =
) + .( - . + =
From equation (1)
.. - . + . =
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Unit one-20-Chapter Three
.
[1.225,15]
Angle of deviation ()
Definition.. :
Factors affected on the angle of deviation:
.
.
.
Tracing the path of the ray through the prism:
The deviation angle decrease by increasing of the
incident angle to a certain value then it increases
by increasing of the incident angle.
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1
Unit one-21-Chapter Three
The ray will
..
1 =
2 =
.
1. =
1.. =
. =
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Unit one-22-Chapter Three
2. =
The immerge ray
Reflected ray
Notes:
From the graph of minimum deviation, when the
angle of incident increases then the angle of
deviation .. until it reaches then
by increasing the angle of incident, the angle of
deviation will.
If the angle of incident is less than the value in
which the graph starts therefore the prism acts as
..
The minimum angle of incident is corresponding to
angle of incident at the second face equal and the emigrant ray will be .. to the
second surface of the prism, and the emerge angle
=
In the case of minimum deviation:
The refracted ray will be .. to the base of prism.
1 = 2 =
A.. =
..........
........ =
And
1 = 2 =
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Unit one-23-Chapter Three
.. - .. =
..........
.................. +=
*
sin
sin=n
+
=
.....
.....sin
.....
..........sin
n
Examples:
In an experiment it was found that the angle of
minimum deviation is 48.2, given that the angle of
the prism is 58.8. find the refractive index of the
material of the prism.
[1.64]
A triangular prism of refractive angle 60 adjusted
to the minimum deviation position; when the angleof min. dev. is 37.2 find its refractive index.
[1.5]
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Unit one-24-Chapter Three
Experiment to determine the ray path through a
glass prism and its refractive index:
The dispersion of light by a triangular prism:
The angle of deviation depends on
.., which depends on ... Therefore,
each color of light going to deviate by a certain angle,
deference than the other color.
Give reason for:
When beam of white light falls on a triangular
prism adjusted in min. deviation, the emergent ray
deviated into different colored rays (spectrum.)
..
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Unit one-25-Chapter Three
The violet ray has the biggest deviation (max. ).
but the red ray has the least deviation (min. .)
..
Question:
The relation between the angle of deviation and
the wavelength of light is (directly / inversely)
proportional.
The relation between angle of refraction at the first
face and angle of incident at the second face is
(directly / inversely) proportional.
Draw a graphical relation between angle of
refraction at the first face 1 and angle of incident
at the second face 2
The mathematical relation is
..
The intersected point with Y axis indicates
The intersected point with X axis indicates
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A
Unit one-26-Chapter Three
Trace the light ray in the opposite figure where n =1.5
The thin prism:
It is a triangular prism, with an angle not more than10. It is always in a position of minimum deviation.
In case of the small angles the angle in radian unit
is equal to its sin.
2
.......2
................ +
=n
...........
................. +=n
n.. + =
.. - . =
= A) - ..(The relation between and A can be drawn as:
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n
Unit one-27-Chapter Three
Mathematical relation :
Slope
The point of intersection with Y-axes=
The point of intersection with X axes =
The relation between and n can be drawn as:
Mathematical relation :
Slope
Factors affects :...
N.B:.
Rule Case of application
......................
All cases Min
deviation
Thin
prism
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Unit one-28-Chapter Three
..
X Min
deviation
Thin
prism
X X Thin
prism
In case of thin prism for the red color:
r =In case of thin prism for the blue color:
b=..
(b - r) known as the angular size; it is also known
as or . or .
.. or..
Define angular size :
..
Give reasons:
Thin prism is always in minimum deviation.
.
Prove that the angular size equals A (nb - nr)
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Unit one-29-Chapter Three
Factors affect angular size:
.
.
A thin prism has an angle of 5 its refractive index
1.6 produces angle of deviation that is equal to
..
[3]
A ray of light falls on a thin prism with an angle of
deviation 4 and its refractive angle 8 its refractive
index is
[1.5]
Depressive power (:)Definition. :
Rule.. :
Prove that:
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1
=
=
n
nrnbrb
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Unit one-30-Chapter Three
Factor affects Depressive Power (:)
.
N.B:.
= y = .. (Relation between for the blue
color and for the red color)
n = ny = .. (Relation between n for the blue
color and n for the red color)
(total = )
b - r (total.. = )
(total = )
b - r (total.. = )
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