•We can see objects only if light from them or
bounces off from them enters your eyes.
Without light we cant see at all.
•Our main source of light is our Sun.
•Light is form of energy. All the organisms on
Earth need it to perform their activities.
Properties of light
a. Light is form of energy
a. Light travels extremely fast and has a speed of 3.0 x 10
(8) ms – 1 in air.
b. Light travels in straight lines within the same medium
c. Light can be reflected when it hits a surface.
d. Light can be refracted when it travels from one
transparent medium to another.
•The path along each which light travels is
called a ray. A ray of light is represented by a
straight line with an arrow to show its direction.
A ray of light
•A beam of light is made up of a bundle of rays. It can
be parallel, divergent or convergent.
•When light hits an
opaque objects, it may
be absorb or reflected.
•Reflection of light
occurs when light
bounces off the
surface of an object. Reflection of light
a. The incident ray is the ray of light that
approaches the light.
b. The reflected ray is the ray of light that bounces
off the surface.
• When the reflected light enters your eyes, we
can see the object.
• The amount and direction of the reflected light
depend on the nature of the surface it hits.
•Mirror sheets of glass and polished metals have
very smooth surfaces.
a.When a parallel beam of light hits a very
smooth surface, it is reflected as a parallel beam.
Regular reflection is said to occur.
b.If all the light that hits a surface is reflected
regularly, sharp images will be produced. That is
why we can see our image on very smooth
•Objects such as paper, cloth and wood appear
smooth but they are actually quite rough.
a.When a parallel beam of light hits a rough
surface, it is scattered. The tiny bumps on the
surface cause the reflected light to head off in all
directions. This type of reflection is called
irregular or diffuse reflection.
b.This type of reflected light enables us to see
the object from any angle.
•Plane mirrors are usually used to demonstrate reflection
because their smooth and flat surfaces reflect all the light
directed at it in a regular and predictable way.
To the observer, the reflected rays seem to come from the other
side of the mirror.
•The image on a plane mirror is
b.Laterally inverted (the left- hand side of the object
appears on the right – hand side of the image)
c.Virtual ( cannot be formed on a screen)
d.Equal in size as the object
e.At the same distance from the mirror as the object.
a. Plane mirrors are used at home in bathrooms
and bedrooms to help in dressing and
combing. They are also used as rear- view
mirror in cars.
b. Two plane mirrors are used in a periscope to
reflect and change the direction of light.
Periscope is used in a submarines to see above
c. A kaleidoscope is a tube containing two or more plane
mirrors. Small pieces of coloured objects are placed
between the mirrors. The light from the objects is
reflected from one mirror to another, forming beautiful
d. Convex mirror produce a wider scope of view. They are
used as security mirrors in shops and wing mirrors of a
car. They are also used as blind corner mirrors on roads
to help users see approaching vehicles round a bend or a
e. Concave mirrors produce magnified images. They are
used as a dentist’s mirror, cosmetic mirrors and in
microscope and telescope.
•Light can pass through transparent media such as water,
air, glass and certain types of plastic.
•Light travels at different speeds in different media.
Therefore, when light passes from one transparent medium
into another, it may slow down or speed up. This change in
the speed of light causes the light to bend or change the
•The bending of the light ray when it enters a medium of
different density is known as a refraction of light.
•When the light travel from a less dense medium to a
denser denser medium, it slows down. The light is refracted
towards the normal.
Light is refracted when it travels from air to glass
•When light is travel from a denser medium to a less
dense medium, it speeds up. The light is refracted away
from the normal.
Light is refracted when it travels from air to water.
•If a light ray hits a transparent medium at a right
angle. The light passes through the medium in a
straight line. The light is not refracted at all.
Refraction does not occur when light hits the transparent medium at
a right angle.
•Refraction of light gives us a false impression of
the dept and position of an object. Here are some
a. Ponds and swimming pools appear shallower
than they really are. This is because light from the
bottom of the pond is refracted as it moves out of
the water into the air. When the refracted light
enters the eyes of an observer, he sees an image of
the bottom of the pond that is swallower than the
real bottom of the pool.
b. Drinking straw in a glass
of water appears bent.
This is because light from
the straw is refracted as it
travels from the water into
the air. When the
refracted light enters the
eyes of the observer, she
sees the image of straw
somewhere above the
bottom of the glass. This
cause the straw to appear
A partially submerged
drinking straw appears bent
due to the refraction of light.
•However, refraction of light can be useful
a.Refraction of light in our eyes enable us to
see. Light that enters our eyes is refracted to
form sharp images on the retina.
b.Lenses make use of refraction of light.
Lenses are used in instruments such as
magnifying glasses, microscopes, telescopes
and overhead projectors.
•When a beam of white light passes through a prism, the
light spreads out of a band of colors in a certain order.
This band of colors is called spectrum. The colors in the
spectrum in order are red, orange, yellow, green, blue,
indigo and violet.
•Dispersion is the splitting or separating of white light
into its spectrum. This occurs because each color is
refracted slightly when it passes through the prism.
•Rainbow is a natural phenomenon due to the
dispersion of light by the tiny raindrops in the
•The color of an opaque objects depends on
-The color of the light that shines on the object
-The color of the light that object absorbs
-The color of the light that the object reflects.
•The color of light that are not absorbed by the
object are reflected and transmitted to our eyes,
giving the objects its color.
A white object appears white in white light
because the object reflects all the colors in
the white light.
A black object appears black in any colored light
because it absorbs all the colors and reflects none.
•A red objects appears red in white light because it reflects
red light only and absorbs all other colors.
If a red rose is in ref light, it is seen as red because it
reflects the red light. However, if the red rose is in green
light, it appears black as it absorbs green light and reflect
If yellow lemon is in blue light, it appears black as it
absorbs the blue light and reflects none.
Our main source of light is from the Sun. light
helps us to see things. Without light, we cannot see
anything. We will be in total darkness. Sunlight also
gives us heat energy and warms our Earth. Without
sunlight, our Earth will be too cold for us to live
Plants make use of the sunlight to produce their
own food through photosynthesis. They turn
carbon dioxide and water into glucose and oxygen.
This is an important process as it provides food to
all living things either directly or indirectly.
The oxygen produced as a by- product is released
into the environment, replenishing the oxygen
supply for the living things to breathe.
As not every place on Earth receives the same
amount of sunlight, they are not heated equally, the
hot air in warmer area will rise and the cold air
from a cooler area will rush in to replace the hot
air. This create winds and breezes.
The heat from the sunlight, besides drying our
clothes, also creates clouds and rains through
the rain cycle. This is very important as rains
cleanses the air and rejuvenate lives.
Sunlight also stimulates our skin to produce
vitamin D, which helps our body to keep the
right amount of calcium and phosphorous.
Deficiency in vitamin D can lead to
osteoporosis in adults and rickets in childrens.
•However, too many sunlight is bad for humans
too. Long exposure in the Sun can cause
sunburn and skin cancer. We should apply sun
protection lotion or cream and cover our skin
when we are in the Sun for too long. In the Sun
for too long without eye protection increases the
chances of developing eye disease such as
cataracts. Cataracts are a form of eye damage
that causes the lens to lose its transparency.
The patients will have cloudy visions.