NCERT Class 8 Science Light Free Study Material PDF

6 LIGHT
6.1
6.2
6.3
6.4
6.5
Light
Reflection of light
Refraction of light
Lens
Human eye
6.1 LIGHT
What is light?
Light is a form of energy.
 Light travels in straight lines. Light travels along paths called rays. A
beam of light is a stream of light energy, or a bundle of rays which
can be parallel, converging or diverging.
 Light travels in vacuum with a speed of 300 million m/s (in standard
form, 3  108
m/s). This is an incredibly high speed, 3 hundred
thousand kilometres in a single second.
6.1.1 Visibility
An object can be seen when light from the object enters our eyes. Objects
which absorb light completely seem white and those objects that reflect
light completely look black.
There are two types of objects –
Luminous objects which give out light of their own eg. sun, stars, flame,
lamp and fireflies.
Non-luminous objects which do not give out light of their own eg.
moon, paper etc. Non-luminous objects have different degrees of
transparency -
 Opaque – objects that do not allow light to pass through. We cannot
see through them. Most of the objects around us are opaque.
 Transparent – objects that allow almost all the light falling on them
to pass through. We can see clearly what is behind a transparent
object.
 Translucent – objects that diffuse or scatter light and allow only
some light to pass through. We cannot see clearly what is behind a
translucent object eg. frosted window and veil. A translucent object
is something that is in between an opaque and a transparent object.
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6.1.2 Sources and propagation of light
The objects from which we obtain light are known as the sources of light. It is of two types – natural
sources (sun, star, etc.) and artificial sources (candle, torch, etc.). When a source of light emits both light
and heat it is called hot source of light and those that emit only light are called cold source of light. All
incandescent bodies are hot sources of light.
Light travels in straight line if the medium is same and this is known as the rectilinear propagation of
light. Images and shadows are formed because of the rectilinear propagation of light.
A shadow is an area where light is blocked by an opaque
object.
Umbra Penumbra
A totally dark shadow A partially dark
shadow
Produced by point
light source
Produced by extended
light source
6.2 REFLECTION OF LIGHT
Reflection is the bouncing of light off an object.
The ray of light falling on any surface is referred to as
the incident ray. The point at which the incident ray
falls on the mirror is the point of incidence. The ray
that comes back from the surface after reflection is
referred as the reflected ray. The perpendicular drawn
at the centre is called the normal at that point. The
angle between the incident ray and the normal is called
the angle of incidence (i). Likewise, the angle
between the reflected ray and the normal is called the
angle of reflection (r).
6.2.1 Types of reflection
Reflection are of two types -
Regular reflection – Reflection from a smooth surface like mirror or polished metal which produces
sharp images with all the beams reflected in only one direction.
Diffused reflection – Reflection from a rough surface when parallel beams of light are reflected in
various different directions or are scattered. NO image is formed in diffused reflection eg. paper has
uneven surface, we cannot see an image of ourselves in an ordinary piece of paper. It is because of
diffused/irregular reflection, we are able to see objects from every direction.

LAWS OF REFLECTION
 The angle of incidence is always equal to the angle of reflection i.e. i = r
 The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.
6.2.2 Plane mirror
Mirror consists of a piece of thin, flat glass with a coating of silver or aluminum on one side protected by
a coat of paint. Images formed by a plane mirror have the following characteristics:
 Virtual (not real and image cannot be caught on screen)
 Same size as that of the object
 As far behind the mirror as the object is in front of it
 Laterally inverted (images turn from left to right)
 Upright
Virtual images are images which seem to be there but no light actually reaches eg. images in mirrors or
enlarged words when magnifying glasses are used to read.
What is the difference between a real and a virtual image?
Real image Virtual image
Can be captured on a screen Cannot be projected or captured on a screen
After reflection, the rays of light actually meet at a
point.
After reflection, the rays of light appear to meet at
a point.
Always inverted Always erect, but laterally inverted

Multiple reflections
Multiple reflections occur when two plane mirrors are held at some angles and an object is placed
between them. Many images can be seen and the number (n) of images formed, if  is the angle of
inclination between two mirrors, is
n
360 360
1; if is even
360 360
; if is odd
 

 
 
 
  
 
 
 
 
Significance of -1 is that it shows the last two images coinciding with each other.
6.2.3 Methods for constructing reflection ray diagrams
Step 1 - Draw a normal
perpendicular to the
mirror from the object.
Step 2 - Measure the
distance of the object to
the mirror, (let it be x
cm). Along the normal,
x cm behind the mirror
is the location of the
image.
Step 3 - Draw a light
ray from the image to
the eye. The ray
between the mirror and
the eye are actual light
ray (to be drawn as
complete line). The rays
behind the mirror are
virtual light rays (to be
drawn with dotted lines)
Step 4 - Join the
incident ray from the
object to the reflected
ray which is drawn
earlier. Finally add the
arrows to indicate the
directions of light rays.
6.2.4 Kaleidoscope
The principle of forming multiple images
by mirrors at an angle to each other is
used in a toy and termed as kaleidoscope.
It comprises of three plane mirrors
inclined at an angle of 60 to each other.
The entire arrangement is placed in a
cylindrical cardboard box with a few
pieces of colored glass at one end. The
mirrors form multiple images of these
glass pieces resulting in beautiful
patterns when seen from the other end.
On rotating the cylindrical box, the pattern changes continuously as the position of glass pieces shifts.

 Exercise 1:
If two plane mirrors are kept at right angles to each other, how many images will be formed?
6.2.5 Spherical mirror
Spherical mirrors are part of spherical reflecting surfaces. They are made from hollow glass spheres. If a
portion of the hollow sphere is cut along a plane and silvered, it serves as a spherical mirror.
If the portion APB is silvered such that the depressed surface becomes
the reflecting surface, then it is called a concave spherical mirror. In
contrast, if the silvering is done to the bulged surface thereby, serving
as the reflecting surface, it is called a convex spherical mirror.
Concave mirror: It is that kind of mirror where reflection takes place
at inner surface while the outer surface is polished.
Convex mirror: It is that kind of mirror where reflection takes place at
outer surface while the inner surface is polished.
6.3 REFRACTION OF LIGHT
Refraction is the bending of light when it passes from one
transparent material to another.
Refraction is due to the different speeds of light in different media.
6.3.1 Effects of refraction
 An object in water appears nearer to the surface than it really is
eg. swimming pools appear shallower than they actually are,
and glass looks thinner than it really is.
 An object half immersed in water appears to be bent at the water surface.
 Refraction allows our eyes to focus.
 Dispersion of white light

6.3.2 Refractive index of a medium
Refractive index is a material constant, defined as the ratio of velocity of light in air or vacuum to the
velocity of light in the medium. It is a measure of optical density of the medium. The denser a material is,
higher is the refractive index of the material. Also, more the refractive index of the medium, more the
light bends while travelling in that medium.
Refractive index for a medium, μ =
/
=
When incident ray travels from rarer to
denser medium, the refracted ray bends
towards the normal.
Whereas when incident ray travels from
denser to rarer medium, the refracted ray
bends away from the normal. Because of
this, the depth of a pond or the thickness of
a glass slab appears to be less than the actual
value.
When a coin is placed in an empty beaker and water is poured into it, the coin appears to be raised. This
happens due to refraction of light. The depth of the coin due to optical illusion is known as apparent
depth and the actual depth is known as the real depth.
The diagram shows the difference between the real depth and the
apparent depth of an object under water. We see the object closer
than its real depth to the surface. We see the object only if the
rays coming from it reaches our eyes. In this picture, ray coming
from the fish reaches the observer’s eye after refraction. Thus,
observer sees the image of the fish at the distance Da from the
surface which is the apparent depth of the fish. On the contrary,
fish sees the objects away from their real distances. These are all
results of the refraction of light.
The relation between the apparent depth and the real depth in terms of refractive index is
μ =
 Exercise 2:
Why does light bend during refraction?
6.3.3 Dispersion
Dispersion is a kind of refraction in which the amount of bending depends on the wavelength i.e. the
color. This is because the speed of light in a medium depends on the color. In general for glass and similar
materials, red light travels faster than blue light, but both slow down compared with the vacuum.
Examples are the colors produced by prisms, diamonds and rainbows.

When white light is passed through a prism, it splits into seven different colours i.e. VIBGYOR (violet,
indigo, blue, green, yellow, orange and red) which is known as the spectrum. In a prism, the amount of
bending depends on the wavelength or color because the speed of light depends on the color. In other
words, the index of refraction depends on the color. Thus, blue light has a higher index of refraction than
red light, and so is bent (refracted) more.
Dispersion by prism
6.4 LENS
Lens is transparent materials usually made of glass or plastic bounded by one curved surface and another
flat surface or by two curved surfaces. Lenses are of various shapes and sizes and used in many optical
instruments like spectacles, magnifying glass, projector, microscope and telescope.
6.4.1 Types of lens
Spherical lens: It is the segment of a sphere that refracts rays of light equally in all meridians.
Concave lens: It has the reflecting surface curved inward and causes light to spread out or diverge, thus
also referred as a diverging lens.
Convex lens: It has outward curves, the ends are narrow and the middle is wide. It is often referred to as a
converging lens as light passing through a convex lens converges to a point. This point is also called as
the focal point. A convex lens can produce either a real or virtual image.
RELATED TERMS
Optical centre: The geometric centre of a curved lens where no deviation of light occurs.

Principal axis: The imaginary horizontal line passing through the optical centre and focus.
Principal focus: The point on the principal axis where light rays traveling parallel to the principal axis
after refraction actually meet (for a convex lens) or appear to meet (for a concave lens).
Focal length: The distance between the centre of lens and its focus.
6.4.2 Images formed by concave lens
Characteristics of the images formed by a concave lens according to the position of the object:
Case 1: When the object is at infinity, the image
formed is
 virtual and erect
 highly diminished
 at the principal focus (F1) in front of the
concave lens.
Case 2: When the object is between infinity and
the optical centre of the lens, the image formed
is
 diminished
 between the principal focus (F1) and the
optical center of the lens.
6.4.3 Images formed by convex lens
Characteristics of the images formed by a convex lens according to the position of the object:
Case 1: When the object is at infinity, the image
formed is
 real and inverted
 highly diminished
 at the focus (F2) on the right side of the lens.
Case 2: When the object is beyond 2F1, the image
formed is
 diminished
 between F1 and F2 on the right side of the lens.

Case 3: When the object is at 2F1, the image
formed is
 same size as the object
 at 2F2 on the right side of the lens.
Case 4: When the object is between 2F1 and F1, the
image formed is
 enlarged
 beyond F2 on the right side of the lens.
Case 5: When the object is at F1, the image formed
is
 highly enlarged
 at infinity on the right side of the lens.
Case 6: When the object is between F1 and the
optical centre of the lens, the image formed is
 enlarged
 in front of the lens.
6.5 HUMAN EYE
6.5.1 Structure of the eyes
The eye is our organ of sight. The eye has a number of components which includes –
 Cornea: clear front window of the eye that transmits and focuses light into the eye.
 Iris: colored part of the eye, situated behind the cornea; helps regulate the amount of light that enters.
 Pupil: dark aperture in the iris that determines how much light is let into the eye.
 Lens: transparent convex structure of variable thickness that focuses light rays onto the retina.
 Retina: nerve layer that lines the back of the eye, senses light, and creates electrical impulses that
travel through the optic nerve to the brain.
 Optic nerve: connects the eye to the brain and carries the electrical impulses formed by the retina to
the visual cortex of the brain.
 Rods: sensitive to dim light, can detect colour
 Cones: cells present in retina, sensitive to bright light
 Blind spot: spot of no sensory cells in the retinal region at the junction of optic nerve and retina.

 Ciliary muscles: moves the lens to enable light from objects at different distances to be focused on
the retina; the process is called accommodation.
 Aqueous humour: transparent liquid present in the region between the cornea and lens.
 Vitreous humour: clear, jelly-like substance that fills the middle of the eye i.e. the region between
the lens and retina.
The inner surface of the eye is known as the retina. The retina contains the rods and cones that serve the
task of detecting the intensity and the frequency of the incoming light. An adult eye is typically equipped
with up to 120 million rods that detect the intensity of light and about 6 million cones that detect the
frequency of light. These rods and cones send nerve impulses to the brain. The nerve impulses travel
through a network of nerve cells. There are as many as one million neural pathways from the rods and
cones to the brain. This network of nerve cells is bundled together to form the optic nerve on the very
back of the eyeball.
By changing the focal length, (accommodation) the lens is able to focus light onto the retina for objects
located at various distances. The relaxed eye can easily focus on distant objects. To focus on close objects
the lens is squeezed to shorten it’s focal length, making it possible to converge the rays onto the retina.
The near point is the distance at which the closest object can be seen clearly. It recedes with age.
Persistence of vision: Our eye needs one sixteenth of a second to register an image. If the images are
shown at a faster rate, eyes fail to distinguish the images.
6.5.2 Diseases of the eyes
A. Myopia/Short-sightedness
Near-sightedness, also known as short-sightedness and myopia, is a condition of the eye where light
focuses in front of, instead of on, the retina. This causes distant objects to be blurry while close objects
appear normal. The underlying mechanism involves the length of the eyeball growing too long or less
commonly the lens being too thick. It is a type of refractive error.
It can be corrected by using spectacles with concave lens as they diverge the light rays and images form
on retina.

Myopia
B. Hypermetropia/Long-sightedness
Far-sightedness, also known as hyperopia, is a condition of the eye in which light is focused behind,
instead of on, the retina. This results in close objects appearing blurry, while far objects may appear
normal. As the condition worsens, objects at all distances may be blurry. The cause is an imperfection of
the eyes. Often it occurs when the eyeball is too short, or the lens or cornea is misshapen.
It can be corrected by using spectacles with convex lens as they converge the light rays and images form
on retina.
Hypermetropia
C. Cataract: A cataract is a clouding of the lens in the eye which leads to a decrease in vision. Cataracts
often develop slowly and can affect one or both eyes. They are most commonly due to aging but may also
occur due to trauma or radiation exposure.
D. Blindness: Loss of vision; may be due to injury or disease or by birth.
E. Colour blindness: It is the decreased ability to see color or differences in color. It is usually hereditary
and individuals have lesser cones to sense the colours.
F. Night blindness: It is caused by near-sightedness, cataract or deficiency of Vitamin A in the diet.
6.5.3 Care of the eyes
Eyes are very important organ and they are sensitive too. So, proper care of eyes is very important. Some
tips for care of eyes are as follows:
 Do not read in too bright or too dim light.
 Do not look directly at a bright object or at the sun.
 Do not keep the book too close to your eyes; while reading. Don't keep the book too far either.
 If something gets into the eye, do not rub the eye. Wash it with cold water.
 In case of any problem; like itching or burning sensation; consult an ophthalmologist.

6.5.4 Educating visually challenged persons
Visually challenged persons need special training to learn, read and write. Since they depend a lot on the
sense of feeling and hearing, they often develop a keen sense of touch and hearing.
Braille is a tactile writing system used by people who are visually impaired. It is traditionally written
with embossed paper. Braille is named after its creator, Louis Braille, a Frenchman who lost his sight as a
result of a childhood accident. In 1824, at the age of fifteen, he developed a code for the French alphabet
as an improvement on night writing. These characters have rectangular blocks called cells that have tiny
bumps called raised dots. The number and arrangement of these dots distinguish one character from
another. Since the various braille alphabets originated as transcription codes for printed writing, the
mappings (sets of character designations) vary from language to language.
ANSWERS TO EXERCISE
Exercise 1: For  = 90, =
°
°
− 1 = 4 − 1 = 3
Exercise 2: Light bends during refraction because the velocity of light is different in different
mediums.

Solved Examples
Example 1
An opaque paper when oiled becomes translucent. Why?
Solution
 Amount of light getting absorbed, reflected and transmitted in case of opaque and translucent object.
 Difference in transmission of light from pores of oiled paper to that of ordinary paper.
Example 2
Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the
room? Explain.
Solution
We can see any object, when light reflected by that object reaches to our eyes. But in the dark room, no
light is reflected by the object. Hence, we are not able to see the objects in dark room. But if there is
light outside the room, we can see the objects lying out there.
Example 3
Light enters from air to glass plate having refractive index 1.5. What is the speed of light in glass?
The speed of light in vacuum is 3  108
m/s.
Solution
Refractive index μ =
/
⇒ 1.5 =
×
⇒ =
×
.
= 2 × 10 m/s
Example 4
Find the position of the image of an object placed at a distance of 10 cm from a convex mirror of
focal length 10 cm.
Solution
Given, object distance u = -10 cm (by using sign convention)
Focal length of the mirror, f = 10 cm
From mirror formula, = + we have = + ⇒ = + = = ⇒ = 5 cm
Example 5
Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the
laws of reflection?
Solution
Regular reflection Diffused reflection
Takes place from a smooth surface Takes place from a rough surface
Reflected rays move in a particular direction Reflected rays scatter in random directions.
Example – Reflection by plane mirror Example – Reflection by road
Diffused reflection is not because of the failure of the laws of reflection but due to the irregularities in
the reflecting surface.
Example 6
A point source S is placed in water. Name the type of beam of light it emits. This beam of light after
coming out from water converges or diverges why?

Solution
A point source always emits a diverging beam of light. When this beam of light comes out of water, it
diverges. This is because the refracted rays move away from the normal.
Example 7
Why does a concave lens always form a virtual image of an object? Draw a diagram to illustrate this.
Solution
The rays falling on a concave lens, after refraction always diverge. Therefore no matter where the object
is kept, a diverging lens always forms a virtual image, which is erect and smaller in size than the object.
It is formed between the optical center and the focus, on the same side of the lens as the object.
Example 8
Mention against each of the following whether regular or diffused reflection will take place when a
beam of light strikes. Justify your answer in each case.
(a) Polished wooden table, (b) Chalk powder, (c) Cardboard surface, (d) Marble floor with water
spread over it, (e) Mirror and (f) Piece of paper
Solution
(a) A polished wooden table is an example of smooth surface. So, when a beam of light reflects from it,
a regular reflection will take place.
(b) Chalk powder has irregular surface. So, when a beam of light reflects from it, a diffused reflection
will take place.
(c) A cardboard has irregular surface. So, when a beam of light reflects from it, a diffused reflection will
take place.
(d) A marble floor with water spread over it provides a smooth surface. So, when a beam of light reflects
from it, a regular reflection will take place.
(e) A mirror has a smooth surface. So, when a beam of light reflects from it, a regular reflection will take
place.
(f) A piece of paper may appear smooth but it has many minor irregularities. So, when a beam of light
reflects from it, a diffused reflection will take place.
Example 9
How many images of a candle will be formed if it is placed between two parallel plane mirrors
separated by 40 cm?
Solution
Infinite number of images

Example 10
Why can the sun be seen two minutes before actual sunrise and two minutes after actual sunset?
Solution
When light rays passes through the atmosphere having layers of different densities and refractive
indices, then atmospheric refraction takes place. The actual sunrise takes place when the sun is above
horizon. When the sun is just below the horizon, the light rays coming from it on entering the Earth's
atmosphere suffer atmospheric refraction from a rarer to denser medium and thus, they bend towards the
normal at each refraction. Due to continuous refraction of light rays at each layer, it follows a curved
path and reaches the eye of the observer. As a result, we can see the sun 2 minutes before it rises above
the horizon in the morning. It is also due to refraction that we can still see the sun for about 2 minutes
even after the sun has set below the horizon. As a result, the time from sunrise to sunset is increased by
about 4 minutes.
Example 11
Describe an activity to show that the incident ray, the reflected ray and the normal at the point of
incidence lie in the same plane.
Solution
Fix a white sheet of stiff paper on a drawing board or a table. Take a comb and close all its openings
except one in the middle. Hold the comb perpendicular to the sheet of paper. Throw light from a torch
through the opening of the comb from one side. With slight adjustment of the torch and the comb we
will see a ray of light along the paper on the other side of the comb. Keep the comb and the torch steady.
Place a strip of plane mirror in the path of the light ray. Let the sheet project a little beyond the edge of
the Table. Cut the projecting portion of the sheet in the middle. Look at the reflected ray. Make sure that
the reflected ray extends to the projected portion of the paper. Bend that part of the projected portion on
which the reflected ray falls. Bring the paper back to the original position.
When the whole sheet of paper is spread on the table, it represents one plane. The incident ray, the
normal at the point of incidence and the reflected ray are all in this plane. When we bend the paper you
create a plane different from the plane in which the incident ray and the normal lie. Then we do not see
the reflected ray. It indicates that the incident ray, the normal at the point of incidence and the reflected
ray all lie in the same plane.

Example 12
Describe the construction of a kaleidoscope.
Solution
A kaleidoscope is made up of three rectangular mirror strips joined together to form a prism. These are
fixed in a circular cardboard like tube or tube of a thick chart paper. The tube is slightly longer than the
mirror strips. One end of the tube remains closed by a cardboard disc having a hole in the centre,
through which one can see. To make the disc durable, a piece of transparent plastic sheet is pasted under
the cardboard disc. At the other end, touching the mirrors, a circular plane glass plate is fixed. On this
glass plate several small pieces of coloured glass is placed to form multiple images.
Example 13
What you meant by rectilinear propagation of light?
Solution
Light travels in a straight line. And this property of light is known as rectilinear propagation of light.
Example 14
What do you mean by Braille text?
Solution
The Braille system employs a series of dots to denote letters. This system enables blind person to read.
Braille symbols are made up of one to six dots, arranged in rectangular block.
Example 15
Explain how you can take care of your eyes.
Solution
It is necessary that we take proper care of our eyes. If there is any problem we should go to an eye
specialist. Have a regular check-up.
 If advised, we should use suitable spectacles.
 Too little or too much light is bad for eyes. Insufficient light causes eyestrain and headaches. Too
much light, like that of the sun, a powerful lamp or a laser torch can injure the retina.
 We should not look at the sun or a powerful light directly.
 Never rub our eyes. If particles of dust go into our eyes, wash our eyes with clean water. If there is no
improvement go to a doctor.
 Wash our eyes frequently with clean water.
 Always read at the normal distance for vision. Do not read by bringing your book too close to our
eyes or keeping it too far.

Example 16
Differentiate between yellow spot and blind spot.
Solution
Blind spot Yellow spot
It lies a little away from the yellow spot. It lies exactly opposite the centre of the cornea.
It contains no pigment. It has yellow pigments.
Optic nerves start from this spot. No nerves start from this spot.
It lacks a depression. It has a shallow depression, the fovea centralis, at
its middle.
It lacks visual receptors and is insensitive to light. It lacks visual receptors and is sensitive to light.
The eye coats are absent at blind spot. The eye coats are present at yellow spot.
No image is formed at this place. Image is formed at this place.
Example 17
If two mirrors are placed at an inclination of 30° then how many images can be seen?
Solution
For  = 30, =
°
°
− 1 = 12 − 1 = 11
Thus, 11 images are formed.
Example 18
What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
Solution
We know that angle of incident ray is equal to angle of reflected ray i.e.  = 
But it is given that  +  = 90° ⇒  +  = 90° ⇒ 2 = 90° ⇒  =
°
= 45°
Example 19
Give two uses of plane mirror.
Solution
 Plane mirrors are used to reflect light on an object. For example, during outdoor shooting of a film,
metal sheets are used as plane mirrors to reflect sunlight on the actors.
 They are also used in solar cookers to reflect light on the food being cooked. They are used in
periscopes also.
Example 20
State the functions of –
(i) Optic nerve
(ii) Cornea
(iii) Choroid
Solution
(i) Transmission of optical impulse to the brain.
(ii) This allows light to enter the eye.
(iii) This keeps the interior part of the eye ball dark by preventing internal reflections.
Example 21
Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in
figure. Draw the reflected ray from the second mirror.

Solution
Example 22
What is refraction? Show the refraction of light through glass.
Solution
Although light usually travels in straight lines through optical materials, something different happens at
surfaces. Light is bent as it passes through a surface where the refractive index change, for example as it
passes from air into glass. The amount of bending depends on the refractive indexes of the two media
and the angle at which the light strikes the surface between them.
******

EXERCISE
 Multiple choice questions with one correct answer
1. When the angle between two plane mirrors is 30, how many images will be formed by the mirrors?
(A) 10 (B) 12 (C) 11 (D) 8
2. All light rays are said to be convergent when
(A) all the rays travel parallel to each other
(B) all the rays spread from a point source of light
(C) all the rays converge towards a single point
(D) it travels in an irregular pattern
3. Part of the eye which controls the light entering is called
(A) iris (B) cornea (C) lens (D) retina
4. In lateral inversion,
(A) right side of the object will be right side of the image
(B) left side of the object will be left side of the image
(C) upside of the object will be downside of the object
(D) right side of the object will be left side of the image
5. An object is placed at a distance x from a convex mirror of focal length 15 cm when an image is formed
at a distance of 6 cm behind the mirror. The value of x is
(A) – 15 cm (B) – 10 cm (C) – 25 cm (D) None of these
6. Which object uses the reflection of light?
(A) Kaleidoscope (B) Plane mirror (C) Side mirror of a car (D) All of these
7. Refractive index of glass with respect to air is 1.5 and refractive index of water with respect to air is 4/3.
What will be the refractive index of glass with respect to water?
(A) 1 (B) 1.5 (C) 1.125 (D) 1.4
8. Mira is observing her image in a plane mirror. The distance between mirror and her image is 4 m. If she
moves 1 m towards the mirror then the distance between she and her image will be
(A) 3 m (B) 5 m (C) 6 m (D) 8 m
9. The nature of the image formed by the concave mirror when the object is placed at the center of
curvature is
(A) real, erect, of same
size
(B) real, erect, of
enlarged size
(C) real, inverted, of
diminished size
(D) real, inverted, of
same size
10. A boy walks towards a mirror at a speed of 2.5 ms-1
. At what speed is his image approaching him?
(A) 1.0 ms-1
(B) 2.0 ms-1
(C) 3.0 ms-1
(D) 5.0 ms-1
11. The danger signals installed at the top of tall buildings are red in color. These can be easily seen from a

distance because among all other colors because the red light
(A) is scattered the most by smoke or fog
(B) is scattered the least by smoke or fog
(C) is absorbed the most by smoke or fog
(D) moves fastest in air
12. We can see a non-luminous object when light
(A) emitted by the object falls on the eye.
(B) is reflected from the object towards our eye.
(C) completely passes through the object.
(D) gets completely absorbed by the object.
13. At a particular time during day, the ratio of height of an object and the length of its shadow is x. Using
this, calculate the height of a tree if the length of the shadow of tree is L.
(A) x/L (B) x L (C) x + L (D) L - x
14. Which surface won’t reflect most of the light falling on them?
(A) Rough surface (B) Shining surface (C) Smooth surface (D) Opaque surface
15. The light from the sun takes 500 secs to reach the earth. Assuming the speed of light is 300000 kms-1
,
calculate distance between the sun and the earth.
(A) 100 million km (B) 150 million km (C) 200 million km (D) 300 million km
16. A virtual image larger than the object can be produced by a
(A) Concave lens (B) Concave mirror (C) Convex mirror (D) Plane mirror
17. A spectrum is obtained by sending a beam of white light through a prism. A second prism exactly
similar to the first one is placed in an inverted position with the sides parallel to the first. Now
(A) a new spectrum will be formed on the screen with double the number of colors present in the
previous spectrum
(B) new spectrum will be obtained on the screen with only half the number of colors present in the
previous spectrum
(C) previous spectrum will disappear and we will obtain a white light formed by the fusion of colors
(D) a spectrum with same number of colors present in the previous spectrum will be formed but their
wavelengths will be increased twice.
18. The ENT doctor uses a
(A) Convex mirror (B) Convex lens (C) Plane mirror (D) Concave mirror
19. Which of the following statements is correct regarding rods and cones in the human eye?
(A) Cones are sensitive to dim light.
(B) Cones are sensitive to bright light.
(C) Rods are sensitive to bright light.
(D) Rods can sense colour.

20. Incident angle of a ray of light is 30. The angle between the incident ray and the reflected ray is
(A) 30 (B) 60 (C) 90 (D) 15
 Fill in the blanks
21. Twinkling of stars is due to atmospheric ________ of light by different layers of varying refractive
index.
22. ________ lens is preferred while reading small letters found in a dictionary.
23. Glow worm is an example of ________ source of light.
24. A ray of light incident along normal to the mirror ________ its path.
25. Light entering the eye lens ________ when eye muscles contract and the lens become thicker.
 True or False
26. Air is an example of transparent medium.
27. Reflection by a looking mirror is called regular reflection.
28. If two mirrors are inclined at an angle of 60 and an object is placed between them, 6 images of the
object are formed.
29. Luminous object act as source of light.
30. In concave spherical mirror, the image formed is always virtual.
31. Light particles possess elastic property.
32. Rainbow is formed due to light dispersion.
 Solve the following
33. What is reflection of light? Explain it with a neat diagram.
34. Which of these mirrors converge a parallel beam of light – plane, concave or convex?
35. Why is a convex lens used as simple magnifying glass?
36. Why do we need a shiny surface for reflection?
37. Name the part of the eye which gives colour to the eyes.
38. Match the following.
Column 1
a) Rubber
b) Greased paper
c) Real image
d) Virtual image
Column 2
p) Translucent medium
q) Opaque medium
r) Erect
s) Inverted
39. The angle between incident ray and reflected ray is 60°. What is the value of angle of incidence?
40. What happens to light when it gets dispersed? Give an example.

41. What kind of mirror is used by dentists to view the magnified images of teeth?
42. What kind of lens is there in our eyes? Where does it form the image of an object?
43. What is a rainbow?
44. What is the nature of image formed by convex mirror?
45. How is the phenomenon of reflection used in making a kaleidoscope? What are the applications of a
kaleidoscope?
46. Bala while waving his hand very fast in front of his eyes, observes that his fingers appear blurred. What
could be the reason for it?
47. Draw a neat labeled diagram of the structure of eye and describe its various parts.
48. A light ray makes an angle of incidence 60 when it falls on a plane reflecting sheet.
a) What will be the glancing angle of reflection?
b) What will be the angle of reflection?
c) What will be the angle of deviation?
49. Differentiate between the following –
a) Rods and cones
b) Regular reflection and diffused reflection
c) Images formed by concave mirror and convex mirror
d) Myopia and hypermetropia
50. How many images are formed when two plane mirrors are kept at angle of 60?
51. What is meant by lateral inversion?
52. How many times is a ray of light reflected by two plane mirrors placed parallel and facing each other?
53. Write the properties of the image formed by the following –
a) plane mirror
b) convex mirror
c) concave mirror
d) convex lens
e) concave lens
54. Why does a thick mirror show a number of images of a candle flame?
55. How many colours are there in sunlight?
56. A plane mirror reflects sunlight to form a bright patch on the wall but a crushed aluminium foil gives a
less bright patch. Why?
57. Name the triangular piece of glass that splits white light into different colors.
58. Describe with neat diagrams, the nature of the images formed by a convex lens when an object is placed
at different locations like a) infinity, b) between 2F and F and c) between F and optical centre.
59. Which part of the eye gets affected if someone is suffering from cataract? How is it treated?

60. What is a spectrum?
61. The distance between the object and its image formed by a plane mirror appears to be 24 cm. What is the
distance between the mirror and the object?
62. The characters in the Braille code are based on the arrangement of how many raised dots?
63. Explain your little sister how she can properly take care of her eyes.
64. Power of lens is defined as the ability to converge the rays of light falling on it i.e.
=
1
ℎ ℎ ( )
It may be positive or negative depending on the types of lens. SI unit of power of a lens is diopter (D).
a) What is the power of a concave lens?
b) Focal length of a convex lens is 25 cm. Find the power of this lens.
c) What shall be the power of a thin glass plate?
65. Eyes of the nocturnal birds have large cornea and a large pupil. How does this structure help them?
******

Answers
1. (C) 2. (C) 3. (A) 4. (D) 5. (B) 6. (D)
7. (C) 8. (C) 9. (D) 10. (D) 11. (B) 12. (B)
13. (B) 14. (A) 15. (B) 16. (B) 17. (C) 18. (D)
19. (B) 20. (B)
21. refraction 22. Convex 23. natural 24. retraces
25. increases
26. True 27. True 28. False 29. True 30. False
31. False 32. True
34. Concave 37. Iris 38. a-q, b-p, c-s, d-r 39. 30°
41. Concave 42. Convex, retina 44. virtual, erect 48. 30, 60, 60
50. 5 52. Infinite times 55. 7 57. Prism
59. Lens 61. 12 cm 62. 6 64. negative, 4 D, 0
******

Additional Notes for Competitive Exams
USES OF REFLECTION
Reflecting
surface
Concave Convex Plane
Image Larger than the actual object if the
object is near the mirror
Wider scope of view,
upright images
Same size as the object
Uses Cosmetic mirror, dentist’s mirror,
microscope, car headlights and
searchlights
Blind corner mirrors, car
wing mirrors
Periscope, Kaleidoscope
MIRROR EQUATION
The ray tracing technique shows qualitatively where the image will be located. The distance from the mirror to
the image, v, can be found from the mirror equation:
1
=
1
+
1
where u = distance from object to mirror; v = distance from image to mirror and f = focal length.
Sign conventions:
 u is positive if the object is in front of the mirror (real object).
 u is negative if the object is in back of the mirror (virtual object).
 v is positive if the image is in front of the mirror (real image).
 v is negative if the image is behind the mirror (virtual image)
 f is positive for concave mirrors
 f is negative for convex mirrors
SNELL’S LAW
In general, when light enters a new material its direction will change. The angle of refraction θ2 is
related to the angle of incidence θ1 by Snell’s law:
=
where v is the velocity of light in the medium. The angles θ1 and θ2 are measured relative to the line normal to
the surface between the two materials.
******

Worksheet 1
1. Label the given picture of an eye.
2. Define the following terms.
(a) Pupil
(b) Retina
(c) Blind spot
(d) Optic nerve
(e) Lens

Worksheet 2
1. Give reasons of the following.
(a) Objects appear of a particular colour only.
(b) Reflections are irregular.
(c) Sun rays are called white light.
(d) Eye care is important.
(e) The images formed with the plane mirror show lateral inversion.
(f) PS
2. Give difference between myopia and hypermetropia.

Answers
Worksheet 1
1.
2. (a) The inner aperture that we can see in the centre of the eye is known as pupil. it is a small hole
through which the light enters.
(b) This lies behind the eyeball. The image is formed on the retina.
(c) This portion does not have any rods and cones. This is a position on the retina where image
formation does not take place.
(d) It carries impulses from the eyes to the brain.
(e) This is the transparent tissue between the pupil and the retina. The lens helps in focusing the light
that passes through the pupil into the eye.
Worksheet 2
1. (a) An object appears to be of a particular colour because it absorbs all the colours except the one it is
made up of.
(b) When the beam of light falls on rough surfaces, the light is reflected in different directions and
results in irregular reflections.
(c) Sunlight consists of seven colours known as VIBGYOR which appear to our eyes as white.
(d) Eyes are a very important organ of our body. Eye health has a very strong relationship with the food
we eat. So we should eat healthy food to take proper care of eyes.
(e) The image shows lateral inversion, the right side of the object appears to be the left side of the
image.
2. Myopia: This is also called short sightedness. In this defect, the person cannot see the objects that are
far away clearly. This defect can be rectified by wearing spectacles with concave lenses.
Hypermetropia: This is also called long sightedness. In this defect, the person cannot see the nearby
objects clearly. This defect can be rectified by wearing spectacles with convex lenses.
******

NCERT Class 8 Science Light Free Study Material PDF

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NCERT Class 8 Science Light Free Study Material PDF