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Screen
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1.
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Section
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Prerequisites and Learning objectives
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Screen Title
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The Human Eye and the Colourful World
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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1.
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Prerequisites:
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Prerequisites:
To start this
chapter requires a firm understanding of the following:
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2.
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Learning objectives:
Atmospheric refraction
And Scattering of light
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Learning objectives:
After completing this
chapter student will able to:
Atmospheric
refraction
And Scattering of light
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Reference
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Screen
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2.
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Section
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Introduction
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Screen Title
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The Human Eye and the Colourful World
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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3.
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Show image formation by lenses.
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Introduction:
·
What is refraction of light?
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Introduction:
·
What is refraction of light?
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4.
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Show
reflection and refraction by animation
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‘Light - Reflection and Refraction’
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We can give the answers
to above questions based on previous knowledge which is studied in the
chapter ‘Light- Reflection and
Refraction’.
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5.
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Show
the eye image/animation:
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These ideas can help us to study of the human eye.
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Reference
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Screen
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3.
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Section
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Explanation
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Screen Title
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11.1 THE HUMAN EYE
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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1.
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Rotate the eye from front view to side view and
stop cam.
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The human eye: is the most valuable and sensitive sense organ and it is a natural
optical instrument. The eye is nearly spherical in shape with a slight bulge
in the front part, and it enables us to see the beautiful, colorful world
around us.
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2.
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Indicate
all the labels as per VO.
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The important parts of the eye:
Cornea:
Iris:
Pupil:
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Let us discuss about the important parts of the eye and their
functions:
Cornea: The front part of the eye is covered by transparent spherical membrane
called cornea. Light enters the eye
through cornea.
Iris: Just behind the cornea is a dark coloured muscular diaphragm which has a small
circular opening in the middle.
Pupil: Pupil is the small circular opening of iris. The pupil appears black
because no light is reflected from it.
The dark center in the middle of the
iris. The pupil determines how much light is let in to the eye. It changes sizes to accommodate for the
amount of light that is available.
The iris regulates the light by adjusting
the size of the pupil.
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3.
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Let us see how iris regulates and controls the amount of light
entering the eye:
When the intensity of light is more or if
it is a bright source of light then the iris makes the pupil to contract and
as a result the amount of light entering the eye decreases.
When the intensity of light is less or if
the light is dim then the iris dilates the pupil so that more light can enter
the eye.
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4.
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Eye Lens:
Retina:
Blind Spot:
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Eye Lens: The
eye lens is a convex lens made of a transparent jelly - like proteinaceous
material. The eye lens is hard at the middle and gradually becomes soft
towards the outer edges. The eye lens is held in position by ciliary muscles.
The ciliary muscles help in changing the curvature and focal length of the
eye lens.
Retina: The inner back surface of the eye ball is called
retina. It is a semi-transparent membrane which is light sensitive and is
equivalent to the screen of a camera. The light sensitive receptors of the
retina are called rods and cones. When light falls on these receptors they
send electrical signals to the brain through the optic nerve. The space
between the retina and eye lens is filled with another fluid called vitreous
humour.
Blind Spot: It is a spot
at which the optic nerve enters the eye and is insensitive to light and hence
the name.
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5.
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Accommodation of the eye
Power of Accommodation
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Let us discuss about Accommodation of the eye and Power of Accommodation.
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6.
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Show
the movement of (expansion and compression) ciliary muscles when falling
light.
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Accommodation of the eye:
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Accommodation of the eye: The
process by which the ciliary muscles change the focal length of an eye lens
to focus distant or near objects clearly on the retina is called the accommodation
of the eye.
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7.
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Muscles
are expansion and the eye lens become thin.
Muscles are compress and the eye lens become
thick.
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Power
of Accommodation: The ability of the eye to
focus objects lying at different distances is called the power of
accommodation of the eye.
How Does an Eye Focus
Objects at Varying Distances?
When the ciliary muscles are relaxed, the eye lens becomes thin. Thus, its focal length increases and we see the
distant objects clearly.
When the ciliary muscles are contract, then the curvature of the
eye lens is increases and the eye lens becomes thick.
Thus, its focal length decreases and we see the nearby objects.
In brief it is the adjustment of the focal length of the eye lens which enables us to focus on objects situated at different distances. |
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8.
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Show
the following animation:
A boy see near object, show wit camera animation
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Least Distance of Distinct Vision (Near
point):
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Least Distance of Distinct Vision (Near point): Near point or least distance of distinct vision is the point
nearest to the eye at which an object is visible distinctly.
For a normal eye the least distance of distinct vision is about 25 centimetres. However, it varies with age of the person. For example, for infants it is only 5 to 8 cm. |
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9.
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Show
the far point of the eye.
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The
far point of the eye:
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The
far point of the eye:
Far point of the eye is the maximum distance up to which the normal eye can see things clearly. It is infinity for a normal eye. |
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10.
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Show the
milky and cloudy eyes in old
character
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Indicate
labels as per the words(bold) in VO.
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Cataract:
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Cataract: The crystalline lens of people at old age becomes milky and cloudy. This condition is
called cataract. This causes partial or complete loss of vision. It is
possible to restore vision through a cataract
surgery.
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11.
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Show
the distance between the near and the far point.
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Range of Vision:
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Range of Vision: The distance between
the near point and the far point is called the range of vision.
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Reference
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Screen
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4.
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Section
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Explanation
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Screen Title
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11.2 DEFECTS OF VISION AND THEIR CORRECTION
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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1.
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DEFECTS OF VISION AND THEIR CORRECTION:
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DEFECTS OF VISION AND THEIR CORRECTION:
The eye may gradually lose its power of accommodation.
In such conditions, the person cannot see the objects distinctly and comfortably.
The vision becomes blurred due to the refractive defects of the eye.
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2.
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Show
the types of defects of eye in tree
diagram with lables.
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There are mainly three common refractive defects of vision. These
are
(i)
Myopia or near-sightedness,
(ii)
Hypermetropia or farsightedness,
and (iii) Presbyopia.
These defects can be corrected by the use of suitable spherical
lenses.
We discuss below these defects and their correction.
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3.
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Show
the following animation:
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Myopia: The light from a distant object
arriving at the eye lens may get converged at a point in front of the retina
in the vitreous body. This type of defect is called near sightedness or
myopia.
The correction for myopia:
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Myopia: The light from a distant object arriving at the eye lens may get
converged at a point in front of the retina in the vitreous body. This type
of defect is called near sightedness or myopia.
Let us
observe these cases, and then you can understand the concept ‘myopia’.
In the case of
normal eye, the light rays from the object fall on the eye and converge on
the retina.
In the case of myopic eye, the light rays from the object fall on
the eye and focuses the light at a point in front of the retina in the
vitreous body
The correction for myopia:
To compensate
this, we interpose a concave lens between the eye and the object, with the
diverging effect desired to get the image focused on the retina.
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4.
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Show
the formation of image in hypermetropic eye, normal eye and its correction
with ray diagrams.
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Hypermetropia: If the eye-lens focuses the incoming light at a point behind the
retina, this defect is called far sightedness or hypermetropia.
The correction for hypermetropic eye:
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Hypermetropia: If the eye-lens focuses the incoming
light at a point behind the retina, this defect is called far sightedness or
hypermetropia.
Let us
observe these cases, and then you can understand the concept ‘hypermetropia’.
In the case of
normal eye, the light rays from the object fall on the eye and converge on
the retina.
In the case of hypermetropic eye, the light rays from the object fall on
the eye and focuses the incoming light at a point behind the retina.
The correction for hypermetropic eye:
A convergent lens is
needed to compensate for the defect in vision.
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5.
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Show
the formation of image in pesbyopic eye, normal eye and its correction with
ray diagrams.
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(c) Presbyopia:
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(c) Presbyopia:
What is presbyopia?
Presbyopia is a common type of
vision disorder that occurs as you age. It is often referred to as the aging eye condition.
Presbyopia results in the inability to focus up close, a problem associated
with refraction in the eye.
How does presbyopia occur?
Presbyopia happens naturally in
people as they age. The eye is not able to focus light directly on to the
retina due to the hardening of the natural lens. Aging also affects muscle
fibers around the lens making it harder for the eye to focus on up close
objects. The ineffective lens causes light to focus behind the retina,
causing poor vision for objects that are up close.
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6.
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Show
the boy (long shot) and his eye lens (close up shot).
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When you are younger, the lens
of the eye is soft and flexible, allowing the tiny muscles inside the eye to
easily reshape the lens to focus on close and distant objects.
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Reference
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Screen
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5.
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Section
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Explanation
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Screen Title
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11.3 REFRACTION OF LIGHT
THROUGH A PRISM
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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1.
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Show
the following animation:
Light
passing through a glass slab.
Show all sides of the prism on the table
with camera movement.
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In the previous chapter You have learnt how light gets refracted
through a rectangular glass slab.
For parallel refracting
surfaces, as in a glass slab, the
emergent ray is parallel to the incident ray.
However, it is slightly displaced laterally.
How would light get refracted through a
transparent prism?
Consider a triangular glass prism. It has two triangular bases and
three rectangular lateral surfaces. These surfaces are inclined to each
other. The angle between its two lateral faces is called the angle of the prism. Let us now do an activity to study the refraction of
light through a triangular glass prism.
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2.
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Show
the following animation:
Take the prism and place on the table as shown that it rests on its triangular base.
Trace the outline of the prism using a
pencil.
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Fix a sheet of white paper on a drawing board
using drawing pins.
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3.
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Here PE is the incident ray,
EF is the refracted ray and FS is the emergent ray.
You may note that a ray of light is entering from air to glass at the
first surface AB. The light ray on refraction has bent towards the normal.
At the second surface AC, the light ray has entered from glass to air.
Hence it has bent away from normal.
Compare the angle of incidence
and the angle of refraction at each refracting surface of the prism.
Is this similar to the kind of bending that occurs in a glass slab?
The peculiar shape of the prism makes the emergent ray bend at an angle
to the direction of the incident ray. This angle is called the angle of deviation.
In this case ∠D is the angle of deviation. Mark the angle of deviation in the
above activity and measure it.
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4.
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Reference
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Screen
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6.
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Section
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Explanation
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Screen Title
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11.4 DISPERSION OF WHITE
LIGHT BY A GLASS PRISM
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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1.
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You must have seen and appreciated the spectacular colours in a
rainbow.
How could the white light of the Sun give us
various colours of the rainbow? Before we take
up this question, we shall first go back to the refraction of light through a
prism.
The inclined refracting surfaces of a glass prism show exciting phenomenon.
Let us find it out through an activity.
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2.
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Show
the following animation:
White
light passing through a glass prism and divided into seven colours.
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If a prism is placed in a room and a narrow beam of white
light is allowed to fall on one of its refracting faces,
What do you observe?
It is found that light
coming out from the other face of the prism is split in to seven colors.
What are the seven colours that you see on the
screen?
The various colours seen are Violet, Indigo, Blue, Green, Yellow,
Orange and Red.
This phenomenon (the splitting of light into its component colours)
is called dispersion of light.
The band of the coloured components of a light beam is called its
spectrum.
Why does this happen?
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3.
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The acronym VIBGYOR will help us to remember the
sequence of colours.
We have seen that white light is dispersed into its seven-colour components
by a prism.
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4.
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Why do we get these colours? Different colours of light bend through
different angles with respect to the incident ray, as they pass through a
prism.
The red light bends the least while the violet the most. Thus the rays
of each colour emerge along different paths and thus become distinct. It is
the band of distinct colours that we see in a spectrum.
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5.
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Place
two glass slabs in similar position and white light is scattered through
first prim it fall on second prism.
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Isaac Newton was the first to use a glass prism to obtain the spectrum
of sunlight. He tried to split the colours of the spectrum of white light
further by using another similar prism. However, he could not get any more
colours. He then placed a second identical prism in an inverted position with
respect to the first prism.
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6.
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Place
two glass slabs in similar position and white light is scattered through
first prism it falls on second prism emerged as white light.
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This allowed all the colours of the spectrum to pass through the second
prism. He found a beam of white light emerging from the other side of the
second prism. This observation gave Newton the idea that the sunlight is made
up of seven colours.
Any light that gives a spectrum similar to that of sunlight is often referred
to as white light.
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7.
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White
light passing through water bubble it is divided into colours as shown in
figure.
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A rainbow is a natural spectrum appearing in the sky after a rain
shower.
It is caused by dispersion of sunlight by tiny water droplets, present
in the atmosphere.
A rainbow is always formed in a
direction opposite to that of the Sun. The water droplets act like small
prisms. They refract and disperse the incident sunlight, then reflect it
internally, and finally refract it again when it comes out of the raindrop.
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8.
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Due to the dispersion of light and internal reflection, different
colours reach the observer’s eye.
You can also see a rainbow on a sunny day when you look at the sky
through a waterfall or through a water fountain, with the Sun behind you.
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Reference
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Screen
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7.
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Section
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Explanation
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Screen Title
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11.5 ATMOSPHERIC
REFRACTION
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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1.
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Show the wavering image
Show the twinkling of stars
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We have observed some natural phenomena in our daily life, such as,
This wavering is thus an effect of atmospheric refraction (refraction
of light by the earth’s atmosphere) in our local environment.
Let us discuss about them.
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2.
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Show the twinkling of a stars is due to
atmospheric refraction of starlight
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Twinkling of stars:
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Twinkling of stars:
The twinkling of a star
is due to atmospheric refraction of starlight.
The scientific name for the twinkling of stars is stellar scintillation (or astronomical
scintillation). Stars twinkle when we see them from the Earth's surface
because we are viewing them through thick layers of turbulent (moving) air in
the Earth's
atmosphere. |
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3.
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Show the above animation and give the lables
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Stars (except for the Sun) appear as tiny dots in the sky; as
their light travels through the many layers of the Earth's atmosphere, the
light of the star is bent (refracted) many times and in random directions
(light is bent when it hits a change in density - like a pocket of cold air
or hot air). This random refraction results in the star winking out (it looks
as though the star moves a bit, and our eye interprets this as twinkling). |
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4.
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Show
the following animation:
The
light ray travels through the earth layers with reflection and reach the
observer as shown in figure.
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Stars closer to the horizon appear to twinkle more than stars
that are overhead - this is because the light of stars near the horizon has
to travel through more air than the light of stars overhead and so is subject
to more refraction. Also, planets do not usually twinkle, because they are so close to us; they appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent). Stars would not appear to twinkle if we viewed them from outer space (or from a planet/moon that didn't have an atmosphere) |
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5.
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The light ray travels through the earth layers
with reflection and reach the observer as shown in figure.
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Apparent position of sun:
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Apparent position of
sun: Because of atmospheric refraction, we do not see the sun (or the stars)
in its true position except when it is directly overhead. As a ray of light from
the sun enters earth’s atmospheric at B, it continuously bends towards radius
of the earth.
The ray of light will reach the observer at O as if it had
come in the direction AO instead of in its true direction BO. Consequently,
we do not see the true position of the sun. It is due to atmospheric refraction
that the sun is visible before actual sunrise and after actual sunset.
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6.
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Sunrise
animation
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Do you know this fact?
The sun appears to rise 2 minutes before the actual rise
and it continues to be seen 2 minutes after it has actually set. Therefore,
the day becomes longer by 4 minutes due to atmospheric refraction.
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Reference
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Screen
Number
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8.
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Section
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Explanation
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Screen Title
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11.6 SCATTERING OF LIGHT
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Events
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Graphics/Animation Details
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On Screen Text
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VO
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1.
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Show
the sunrise and sunset images.
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We have across some wonderful phenomena in our daily life, such as
What is the reason behind these natural phenomena?
For this, first we shall discuss about ‘Scattering of light’.
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2.
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Show
the animation, how the light is scattered when it strikes the atmospheric
particles.
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Scattering of light:
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Scattering of light:
When a beam of
light falls on an atom, it causes the electron in the atom to vibrate. The
vibrating electrons, in turn, re-emit light in all directions. This process
is called scattering.
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3.
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Show
above animation.
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The intensity of scattered light varies
inversely as the fourth power of the wave length of height (1/h4).
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Earth’s atmosphere contains air
molecules and other tiny particles. When light from the sun passes through
the atmosphere, it gets scattered by the large number of particles in the
atmosphere.
According to Rayleigh law, the intensity of scattered light
varies inversely as the fourth power of the wave length of height (1/h4).
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4.
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Show the John Tyndall s photo and give some description.
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Tyndall Effect:
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Tyndall Effect:
John
Tyndall was the first one to
explain about the color of the sky in the year 1859.
He stated that the color blue shatters (scattered) more than that of red
due to the shorter wavelength in a case where the light has to pass through a
clear fluid that contains suspended small particles.
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5.
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The sun light passes through dust particles.
The sun light passes through water particles.
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Our planet earth consists
of various mixtures of particles like smoke, molecules of air, dust particles
and water droplets. These diffused particles reflect the light before
it reaches the earth. The scattering of the light by the colloidal particles
is known as the Tyndall effect.
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6.
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The size of the particles
determines the color of the scattered light.
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The size of
the particles determines the color of the scattered light.
This
statement can be proved with the help of a simple experiment.
Allow a beam of light to
pass through a tank of water with a slight mixture of soap or milk in
it. If you watch the beam from a side you can notice that the beam scatters blue light but when you thoroughly
observe the beam from the end then you will find that the beam is reddened after it has passed through the tank.
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7.
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Sun light ray travels towards earth
atmosphere and
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Why is the colour of the clear Sky Blue?
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Why is the colour of the clear Sky Blue?
Since the wave
length of blue colour is smaller than the wavelength of red colour (
Although violet
light is scattered more than blue light, our eyes are not very sensitive to
violet light.
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8.
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Colour of the Sun
at Sunrise and Sunset:
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Colour of the Sun at Sunrise and Sunset: At the time of sunset or sunrise, the
sun is near the horizon as shown in diagram. The rays from the sun must
travel more kilometers through the atmosphere than at noon. Therefore, more
blue is scattered from the sunlight. The removal of blue leaves the transmitted
light more reddish in appearance. Therefore, sun looks reddish at the sunset
or sunrise.
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9.
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The Raman effect was theoretically
predicted in 1923
The first experimental
observation was made by
C V Raman in 1928.
That is, If light of a definite
frequency is passed through any substance in gaseous, liquid or solid state,
the light scattered at right angles contains radiations not only of the
original frequency (Rayleigh Scattering) but also of some other
frequencies which are generally
lower but occasionally higher than the frequency of the incident
light.
The phenomenon of scattering of light by a substance when the frequencies of radiations scattered at right angles are different (generally lower and only occasionally higher) from the frequency of the incident light, is known as Raman Scattering or Raman effect. The lines of lower frequencies as known as Stokes lines while those of higher frequencies are called anti-stokes lines.
If f is the frequency of the
incident light & f’ that of a particular line in
the scattered spectrum, then the difference f-f’
is
known as the Raman Frequency. This frequency is independent
of the frequency of the
incident light.
It is constant and is characteristic of the substance exposed to the incident
light.
A striking feature of Raman
Scattering is that Raman Frequencies are
identical, within
the limits of experimental error, with those obtained from
rotation-vibration (infrared) spectra of the substance.
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10.
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Uses:
Investigation of biological systems such as the
polypeptides and the proteins in aqueous solution.
Determination of structures of molecules.
RAMAN was awarded the 1930 Physics Nobel Prize for this.
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11.
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Reference
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