Light part -1 consists of the basic knowledge of Light and Shadow

1. Class-VI

2. In this chapter we will learn
• Basic concept of light
• Sources of light
• Types of bodies – luminous and non-
luminous
• Visibility of the moon
• Types of substances- transparent,
translucent & opaque
• Point source of light
• A ray and beam of light.
• Kinds of beam of light

3. • Rectilinear Propagation of Light
• Applications Rectilinear Propagation of Light
pin hole camera
 Principle and working
 Factors on which the size of the image
depends on
• Shadows
 Umbra
 Penumbra
 Natural shadows – Eclipses: Lunar &
Solar eclipse
In this chapter we will learn

4. • Light is a form of energy that affects our eyes to produce the sensation of
vision .
• Light is a form of energy that enables us to see all the things around us.
• The main source of light on the earth is the sun. Plants are able to prepare
their own food using sunlight. Some other objects also give out light.
• Light is a key element in our everyday lives. It guides us throughout the
day, nudging us to wake in the morning and lulling us to sleep at night.
lighting enhances our experience in the work place

5. We are unable to see anything in a dark room. On
lighting of the room things become visible. An objects
reflects the light that falls on it . The reflected light when
received by our eyes enables us to see things.
What makes things visible?

6. Rays of light
• Ray of light: The direction or path along
which, light energy travels in a medium
is called a ray of light. It is represented
by a straight line with an arrow marked
on it.
• Rays of light reflect, or bounce
off, objects just like a ball bounces on
the ground. This reflection of light is
what enables us to see everything
around us.
• We can see the Moon because the
Sun's light is reflected off the Moon's
surface. Light can reflect in different
ways, changing the way objects look

7. • Light energy is used to help
us see – either naturally
using the Sun or fire, or
with manmade objects like
candles or light bulbs.
• Light energy is also used
by plants, which capture
the light energy from the
Sun and use it to produce
their food.

8. • light-producing devices used
everywhere.
 Indoor/outdoor lamps
 TV
 Traffic signs
 Commercial displays
 Car headlights( brake and reversing lights on
cars)
 Taillights
 Mobile phones
 computer monitors

9. Why is light so important?
• It acts as a catalyst during
photosynthesis in plants, and it
provides sustenance for the survival of
plankton in the oceans. Both these
forms of herbal life go on to provide
nutrition to many species, including
human beings.
• Light is the most important tool of
guidance.
• Light is a means of communication.

10. We see the objects around us.
• The light rays propagate in a straight
line. When any object comes in its path
of propagation, it bends back or
reflects back alter striking the object.
The reflected rays come to our eyes
and we see the objects around us.

12. Mind Map

13. • We Have Two Types Sources Of Light
Natural sources of light
Artificial sources of light
Natural Source - These sources produces light naturally (Ex : Sun light). Here no
external energy is required to produce light.
 Artificial Source - They are also called man made source of light
(Ex : Candle, Light, Lantern). Here some form of energy
is given to them to produce light. Like in bulb
we give electric energy to get light energy.

14. Natural
sources of
light

15. Artificial source of light

19. Luminous
• Luminous objects/bodies are
Objects/bodies that do not give out
or emit light of their own.
• Luminous objects can cause the
sensation of light.
• Luminous objects are visible as they
emit light of their own.
• Examples of luminous objects
include: Sun, Stars, Candle, Oil
lamp, Torch, Electrical bulb, Glowing
insects, tube light etc.
Non – luminous
• Non-luminous objects/bodies are
bodies/objects that do not give out
or emit light of their own.
• Non-luminous objects do not cause
the sensation of light.
• Non-luminous objects are visible
because of luminous objects.
• Examples of non-luminous
objects/bodies include: Earth,
Moon, Piece of cloth, Coal, Table,
Chair, Eraser, Pen, Pencil etc

20. • Moon is not a luminous body it is non luminous
• It has no light of its own
• It receives light from the sun
• The sunlight after striking the moon reaches us on earth due to which it is seen shining.
• Moon becomes visible to an observer on earth when sunlight reaches him after striking
the moon

21. • The capacity of light penetration is
what distinguishes objects or
materials from each other. This
factor reduces from transparent to
translucent, while it is zero for
opaque objects. The lesser the
light-absorbing capacity, the more
well-defined the shadow is. An
example of this can be a tree near a
street lamp. Its shadow is
pronounced.

22. • Light transmission capacity
varies from object to object.
Transparent objects allow all
the light to pass through them,
translucent ones allow partial
light to pass, whereas opaque
ones allow no light to pass
through.
• The amount of light that can pass
through an object depends on its
density of molecules. Opaque
objects are the most dense, thus,
allowing no light to pass through.
Translucent objects are less in
density, whereas transparent
ones are the least dense.

24. • A material through which light can pass completely.
• We can clearly see through these objects. They can also be called see-through objects.
• The color of this material depends on the light it emits.
• An object on the other side of this material is clearly visible.
• This concept can be best illustrated with the diagram represented in the image above A wine glass
contains red wine. A torch light focused onto the glass passes through it. Due to this, the color of
the wine is visible too. This is because, all the colors of the spectrum of light are reflected by the
glass. Thus, it is transparent.
List of Transparent Materials
• Spectacle Glass
• Sand timer Window
• Computer screen Prism
• Fish tank Camera Lens

25. • List of Translucent Materials
Wax paper Colored plastic bottle Tracing paper
Frosted glass Jelly Paper cup
Cloud Colored Balloon
• A material through which light can pass partially.
• We can partly see through these objects. They can also be called partially-see-through objects.
• The color of this material depends on the amount of light absorbed, scattered, and reflected.
• An object on the other side of this material is visible to some extent.
• Consider the example of a frosted glass. We can barely see what’s outside the window. This is
because the partially-absorbed light scatters in different directions. The image above represents the
concept of translucency. Light is focused onto a frosted glass having thickness. It allows the light to
pass through it diffusely.

26. • A material through which light
cannot pass at all.
• We cannot see through these
objects. They can also be called
not-see-through objects.
• The color of this material depends
on the light it absorbs.
• An object on the other side of this
material is not visible at all.
• Let us understand this concept through an
example of a red-colored apple. When we look
at it, red color is reflected. This is because, all
the colors of the light spectrum are absorbed
by the apple. No light is passed through the
object. Thus, it is opaque.
• List of Opaque Materials
Wooden cupboard Cardboard
Cell phone Motorbike Monument
Flower pot Dice Metal

28. A Point Of Light

29. • A luminous body such as torch electric
lamp candle emits light and it is called
extended and a point of light
• Point source is particularly localized
emission or source of light at a point which
decreases in proportion to the inverse
square of distance from the source while
extended source are collection of such
point sources of light together.

30. A Ray And A Beam Of Light

31. • Light travels in rays and beams.
• The light given out by a point source spreads in all
directions moving in straight lines the light travelling in any
one direction in a straight line is called a ray of light . A ray
is the path taken by a light
• A group of light rays given out from a source is called a
beam of light .
• A beam of light may be parallel, convergent or divergent.

32. There are 3 types of beams. These are
Parallel beams,
Converging beams and
Diverging beams

33. The beam of light can be of three kinds :
• Parallel beam : the beam of light from a source
at a very far distance has light rays parallel beam
of light
• Divergent beam : the beam of light given out
form a point source at a finite distance spreads
out in different directions
• convergent beam : the beam of light coming
towards a point is called convergent beam of
light

34. • The rectilinear propagation of light means
that light travels in straight lines as a wave. This can
be observed in the well-defined shadows formed
when an object blocks a light source and through the
use of a pinhole camera.
• Rectilinear propagation describes the tendency of
Electromagnetic waves (light) to travel in a straight
line.
• Light only deviates from a straight line when the
medium it is travelling through changes density. This
is called refraction.
• The property of light travelling in a straight line is
called as the rectilinear propagation of light.

35. Applications of Rectilinear propagation of light
The three applications of rectilinear propagation of light:
• Pin hole camera
• Formations of shadows
• Eclipses

36. • A pinhole camera, also known as camera obscure, or
"dark chamber", is a simple optical imaging device in
the shape of a closed box or chamber. In one of its sides is
a small hole which, via the rectilinear propagation of light,
creates an image of the outside space on the opposite
side of the box

37. Principle of pinhole camera
• Pinhole cameras rely on the fact that light travels in
straight lines – a principle called the rectilinear theory
of light.
• This makes the image appear upside down in
the camera.
• When the shutter is opened, light shines through to
imprint an image on photographic paper or film placed
at the back of the camera.

38. Importance of Pinhole camera
• The pinhole forces every point emitting light in the
scene to form a small point on the film, so the image
is crisp. The reason a normal camera uses a lens
rather than a pinhole is because the lens creates a
much larger hole through which light can make it
onto the film, meaning the film can be exposed
faster.

39. Characteristics of the image
formed by the pinhole camera
• The image is real,
• it is formed on the screen
• It is inverted or upside down and small in size
• It is generally smaller in size than the object is far
away from the pinhole camera

40. The size of the image depends on the following factors :
• The distance of the screen from the pinhole and the distance
of object in front of the pinhole on increasing the distance of
screen from the pinhole the size of the image also increases
• If the object is moved away from the pinhole the size of the
image decreases
• Actually ,

41. Uses of a pinhole camera
• A common use of pinhole photography is to capture the
movement of the sun over a long period of time. This
type of photography is called solargraphy.
• Pinhole photography is used for artistic reasons, but
also for educational purposes to let pupils learn about,
and experiment with, the basics of photography.

42. Formations of shadows
• A dark area or shape produced by a body coming between rays of
light and a surface
• A shadow is a dark shape that is formed when an object blocks a
source of light. On a sunny day, practically everything casts a
shadow — including you. Shadow can also act as an action, like
when you shadow, or follow, someone on the first day at a new job.
• A dark figure or image cast on the ground or some surface by a
body intercepting light. Shade or comparative darkness, as in an
area. Shadows, darkness, especially that coming after sunset.
• A shadow is caused by an object blocking light so that it does not
reach a surface. The area in shadow appears black because there is
no light falling on it----it appears dark. In fact most shadows are not
totally black because light usually bounces around the obstruction
off other objects

43. • The umbra refers to the darkest part of
the shadow. If you aim a light source
directly at an object, the blackest
portion of the shadow directly behind
the object is the umbra of the shadow.
In astronomy, if the sun is shining
directly on the western hemisphere of
the earth, the eastern hemisphere is
bathed in darkness, and objects behind
the earth (such as the moon or other
planets) are in the earth’s umbra.
• Penumbra refers to the lighter shading
that hangs on the outskirts of the
umbra. The penumbra is not a true
shadow. The Lighting Design and
Simulation Knowledgebase describes the
penumbra as a gradient: The shading
gradually lessens from shadow to light
as the penumbra stretches away from
the umbra.

44. Special cases of formation of
Shadow
• Formation of umbra alone.
• Formation of umbra and
penumbra both
• Formation of penumbra only

45. • The size of shadow is always
bigger than the size of the
object.
• If you move the screen towards
the object the size of the
shadow decreases.
• If you move the screen away
from the object the shadow
increases in size.

46. • Umbra and Penumbra both are formed
in the shadow because of penumbra
that the shadow is not well defined.
• The umbra is bigger in size than the
object if the object is bigger than the
source and it is of same size as the
object, if the object is of the same size
as the source.
• If you move the screen away from the
object the size of both the umbra and
penumbra increases.

47. • If the size of source of light is bigger than the size
of the opaque object, the size of umbra is very
small.
• If the screen is moved away from the object, the
umbra vanishes and only penumbra remains.
•The penumbra is a half-shadow that occurs
when a light source is only partly covered by
an object.
• for example, when the Moon obscures part
of the Sun's disk.
•The other 2 areas are: Antumbra – the
lighter part of the shadow that begins where
the umbra ends.

48. Eclipses
Eclipses are normally named after their
darkest phase.
An eclipse is an astronomical event that
occurs when one celestial object
moves into the shadow of another.
• Types of eclipses :
 Solar eclipses
 Lunar eclipses

49. Solar eclipse
• A solar eclipse occurs when the moon passes in front of the
sun, blocking it out partially or completely. The eclipse
results in parts of the earth being covered in the shadow of
the moon.
• A solar eclipse occurs when a portion of the Earth is
engulfed in a shadow cast by the Moon which fully or
partially blocks sunlight. This occurs when the Sun, Moon
and Earth are aligned. Such alignment coincides with a new
moon indicating the Moon is closest to the ecliptic plane.
• It is that time when the sun, moon and earth are all in a line,
with the moon coming in between the sun and the earth, and
hence casting a shadow on the earth. This results in the
partial or full eclipse of the sun. This phenomenon is called
a solar eclipse.

50. Solar
eclipse

51. • There are four types of solar eclipses
• Partial solar eclipse
• Total solar eclipse
• Annular solar eclipse
• Hybrid solar eclipse

52. • Partial solar eclipses : During a partial solar
eclipse the Moon appears to take a chunk out of
the Sun. A smiley face crescent Sun is an event in
its own right, but at no point does the Moon block
all of the Sun’s light, so it never gets completely
dark. However, it can be a deeply affecting event
if the Moon covers anything more than about 90%
of the Sun, especially on a clear day when daylight
noticeably dips. How much of the Sun the Moon
blocks will depend on where you are on the
Earth’s surface, but at least some of a partial
eclipse can be viewed from a track many
hundreds of miles wide. A partial eclipse is
potentially dangerous to observe.

53. Total solar eclipse
• Total solar eclipses occur when the new
moon comes between the Sun and Earth and
casts the darkest part of its shadow, the
umbra, on Earth. A full solar eclipse, known as
totality, is almost as dark as night.
• During a total eclipse of the Sun, the Moon
covers the entire disk of the Sun. In partial and
annular solar eclipses, the Moon blocks only
part of the Sun.
• If a solar eclipse is total at any point on Earth,
it is called a total solar eclipse, even though it's
seen as a partial solar eclipses in most areas.

54. • An annular solar eclipse happens when the
Moon covers the Sun's center, leaving the Sun's
visible outer edges to form a “ring of fire” or
annulus around the Moon.
• It happens when the Moon is at apogee – its
furthest point from the Earth in its elliptical
orbit – so the Sun appears slightly bigger in the
sky than the Moon.
• Total darkness doesn’t occur during an annular
eclipse, and solar safety eclipse glasses must be
worn.

55. • A hybrid eclipse is a rare type of solar eclipse that
changes its appearance as the moon's shadow moves
across the earth's surface. Sun, moon, and earth
during a hybrid eclipse.
• A hybrid is a bit of both, a total solar eclipse and an
annular solar eclipse.
• Depending on where you stand in the eclipse track on
the surface of earth, it appears as a total solar eclipse,
whereas at other points it appears as an annular solar
eclipse. They’re very rare and happen about once
every 10 years.
• When is the next hybrid solar eclipse? It’s on april 20,
2023 in australia and timor leste.
• Hybrid solar eclipses are relatively rare. After 2023
there’s a gap of eight years until the next one on
november 14, 2031.

56. Lunar eclipses
• A lunar eclipse occurs when the moon moves into the
earth's shadow. This can occur only when the sun, earth,
and moon are exactly or very closely aligned, with earth
between the other two. A lunar eclipse can occur only on
the night of a full moon
• A lunar eclipse is an astronomical phenomenon. It
happens when the moon passes through the shadow of
the earth which can only occur during a full moon. ... The
reddish-brown color is because some of the sun's light
bends through the earth's atmosphere and shines on
the moon.
• An eclipse in which the moon appears darkened as it
passes into the earth's shadow.

57. Lunar eclipse

58. The phases of the moon are the different
ways the moon looks from earth over
about a month.
As the moon orbits around the earth, the
half of the moon that faces the sun will be
lit up.
The different shapes of the lit portion of
the moon that can be seen from
earth are known as phases of the moon.

59. •The lunar phase or Moon phase is the shape of the directly sunlit portion of the
Moon as viewed from Earth.
•The lunar phases gradually change over the period of a synodic month, as the orbital
positions of the Moon around Earth and of Earth around the Sun shift.
•The Moon has phases because it orbits Earth, which causes the portion we see
illuminated to change. The Moon takes 27.3 days to orbit Earth, but the lunar phase
cycle (from new Moon to new Moon) is 29.5 days.
•The Moon spends the extra 2.2 days "catching up" because Earth travels about 45
million miles around the Sun during the time the Moon completes one orbit around
Earth.

60. The rest of the month we see parts
of the daytime side of the Moon,
or phases. These eight phases are,
• New Moon.
• Waxing Crescent Moon.
• First Quarter Moon.
• Waxing Gibbous Moon.
• Full Moon.
• Waning Gibbous Moon.
• Third Quarter Moon.
• Waning crescent

61. • A lunar month is the amount of time it takes for the Moon to pass
through each of its phases (new moon, half, full moon), and then
return back to its original position.
• It takes 29 days, 12 hours, 44 minutes and 3 seconds for the Moon to
complete one lunar month.

62. New moon
• the new moon is the first
lunar phase, when the Moon
and Sun have the same
ecliptic longitude. At this
phase, the lunar disk is not
visible to the unaided eye,
except when silhouetted
during a solar eclipse.
Daylight outshines the
earthlight that dimly
illuminates the new moon.

63. Waxing Crescent Moon.
• Waxing Crescent Moon.
The Moon does not emit its own
light, shining instead by reflecting
sunlight. ...
The waxing (growing) crescent
Moon rises before noon, transits
the meridian before sunset and
sets before midnight. The waxing
crescent phase repeats every
29.531 days – one synodic
month.

64. First Quarter Moon.
• First quarter: The moon is
90 degrees away from the
sun in the sky and is half-
illuminated from our point
of view. We call it "first
quarter" because
the moon has traveled
about a quarter of the way
around Earth since the
new moon

65. Waxing Gibbous Moon.
• Waxing means that it is
getting
bigger. Gibbous refers to
the shape, which is less
than the full circle of a
Full Moon, but larger than
the semicircle shape of
the Moon at Third Quarter.
With some exceptions,
the Waxing Gibbous
Moon rises during the day,
after noon.

66. Full Moon.
• When the moon has
moved 180 degrees from
its new moon position, the
sun, Earth and
the moon form a line.
The moon's disk is as close
as it can be to being fully
illuminated by the sun, so
this is called full moon.

67. Waning Gibbous Moon.
• A waning gibbous
moon is
a moon between full
and last quarter.
Watch for
this moon phase from
late night through
early morning

68. Third Quarter Moon.
• The Third Quarter
Moon is when the
opposite half of
the Moon is illuminated
compared to the
First Quarter. Which half
you see lit up depends on
where you are on Earth.
The Third or Last Quarter
Moon.

69. Waning crescent
• During the Waning
Crescent Moon phase, the
illuminated part of the Moon
decreases from the lit up
semicircle at Third Quarter
until it disappears from view
entirely at New
Moon. Waning means that it is
getting smaller
while crescent refers to the
curved shape similar to a
banana or a boat.