The Radiance of
Light
Ø
Why is it that he/she couldn’t see every one of us, even when the room is
lit/has light?
Because his/her eyes were closed.
Ø
Then why can’t we see in the dark even with our eyes open?
Because
there is no light, we cannot see without light, light makes things visible.
light must enter our eyes for us to see things
around us.
luminous objects non- luminous objects emit
their own light
Stars like sun, fireflies, lamp, lasers
lighted candle, LED etc
Objects
do not emit their own light
Satellites like moon and earth, table, books
etc.
Ø
What comes to your mind when you hear the word ‘light’?
Sun,
see, visible, energy, light rays, absence of darkness, lamps, etc.
light is a form of energy that gives us the
sensation of sight. An object is visible to us only when the light falling on
the object is reflected. The reflected light reaches our eyes which makes the
object visible.
What
enables you to see things during the day?
Sunlight
Ø What do you do to see
things during the night or in the dark?
Use
light bulbs, candles, tube light, lamp, torch, etc.
Ø
Which of the objects shown here give out light on their own?
Sun, firefly, lamp, stars, glow worm, bulb
Ø
What do you understand by the word ‘natural’?
Something
that is present naturally in the environment
Ø What do you understand by
the word ‘artificial’?
Anything
that is made by human beings, is artificial.
Ø Name some natural sources
of light that you see here.
Sun,
stars, firefly, glow- worm
Ø
Name some natural sources of light that you see here.
Torch, bulb, lamp etc.
The
Moon reflects the light of the Sun falling on it i.e. the moonlight. Hence the
moon is a non luminous object.
Ø What is rectilinear
propagation of light?
Light
travels in a straight line and this is known as rectilinear propagation of
light.
Ø
Explain how are objects visible to us?
Objects
are visible to us only when the light falling on the objects is reflected. The
reflected light reaches our eyes which makes the objects visible.
Ø
What is the difference between luminous and non-luminous objects?
Luminous
objects emit their own light whereas
non- luminous objects do not emit their own light.
Ø
Why is the moon a non-luminous object?
Because
it does not have its own light
Ø How is it then possible
for us to see the moon in the night?
Because
it reflects the light of the sun
If
an object does not emit light, it should reflect light in order to be seen, for
example the wall of the room you are in do not emit light, they reflect the
light from the ceiling lights overhead.
-
Define Reflection of light:
Bouncing
back of light from a surface is called reflection of light.
→Incoming light ray that hits the surface of
an object is called the incident ray
→ The
ray which is reflected back after hitting the surface of an object is called
the reflected ray
→The point where the incident ray falls on a
surface is called point of incidence
->What
is angle of reflection?
The
angle between the normal and the reflected ray is called angle of reflection
Ø Will a polished metal
surface reflect light in the same manner as that of the rough wooden surface?
Why?
No,
because the surface of the of polished metal is smooth whereas the surface of
wood is rough/ not smooth, irregular.
Regular
or specular reflection takes place in
objects having polished surface and diffused or irregular reflection takes
place in objects having rough surface.
Ø
When is a multiple image of an object formed?
When
two plane mirrors are placed together at an inclination on one of their edges,
they together form multiple images of the object.
Ø Name two devices based on
multiple reflection.
Kaleidoscope
and Periscope
Ø
What is a periscope?
It is an optical device that is commonly used
in submarines to view the happenings on the surface of the water while sitting
under water.
Ø
Name the famous scientist who first showed that white light is a mixture of
several colours ?
Sir Isaac Newton
Ø
What is the phenomenon of splitting of white light into its constituent colours
called?
Dispersion
of light
Ø
What happens when a ray of light travels from one medium to the other such as
from air to solid and back to air?
When
a ray of light travels from one medium to the other, it bends from its original
direction. This phenomenon is called refraction of light.
Ø
Which among air or glass is an optically denser medium?
Glass
Ø The speed of the light
will be greater in water, air or glass?
In air
Ø What happens to a ray of
light when it passes from an optically rarer to an optically denser medium?
The
ray slows down and bends towards the normal.
Ø Which colours in the
visible light bend more sharply when the pass from air to glass?
Purple/
violet and blue
Ø What is the shape of the
eye?
Ball,
oval
Ø What will happen if a
person accidently hurt his/her eyes?
May
go blind, vision is damaged, cannot see.
The
eyelids act as the shutter of the eye that protects them from the injury the
human eye is made up of three transparent layer ®
Outermost layer or fibrous tunic composed of cornea and sclera ® Middle layer or vascular
tunic consists of choroid, ciliary body and iris ®
Innermost layer is the retina
Ø What is persistence of
vision?
The
image produced in the human eye is retained for approximately one twenty- fifth
of a second after the object is removed.
Ø Name the vision defects.
Myopia
or shortsightedness, hyperopia or farsightedness.
Ø How hyperopia or
farsightedness is corrected?
Hyperopia
or farsightedness is corrected by using convergent lens.
Ø
What is diabetic retinopathy?
In
this condition the retina of the eye gets damaged due to high sugar content of the
blood in the blood vessels.
