All the concepts from basics of light shadow & reflection for classes 6 to 8

1. Light , shadow
reflections
By - S.V

2. Light
● It is a form of energy which gives heat and light energy.
● The objects that emit light on their own are called as
luminous objects. Example = Sun
● The objects that don't emit light on their own but
reflect light from other objects are known as
non-luminous objects. Example = Moon

3. Translucent, Transparent and opaque objects
● The objects through which light passes are known as
transparent objects.
● The objects through light passes through partially are
known as translucent objects.
● The objects through which light does not pass are
known as opaque objects.

4. SHadow & its characteristics
- The region of darkness behind the object where no light is able
to reach is known as the shadow of object.
- Characteristics of shadow :
1. It is always black, no matter what the colour of the object is.
This is because the shadow is formed in the absence of light
rays.
2. It gives an idea about the shape of an object. It, however, gives
no detail of the object.

5. Reflection
When the light falls on a surface, it is made to bounce back in the
same direction, this phenomenon is known as Reflection of light.
There are 2 laws of reflection, They are :
-The angle of incidence is equal to the angle of reflection
-The incident ray, the normal at the point of incidence, and the
reflected ray, all lie in the same plane

6. Types of reflection
There are 2 types of reflection, They are :
1.Regular reflection
2.Irregular reflection

7. Regular Reflection
When the light reflects on a well polished surface like mirror,
then the light rays are reflected back in a parallel manner, this
type of reflection is known as regular reflection.

8. IRRegular Reflection
When the light reflects on a rough surface like wall, the light
rays reflect back in scattered manner, this type of reflection is
known as irregular reflection.

9. Types of Mirror
There are 2 types of mirrors, They are :
1.Concave mirror
2.Convex mirror

10. Concave mirror
A concave mirror, or converging mirror, has a reflecting surface
that is recessed inward.

11. Convex mirror
A convex mirror is a curved mirror in which the reflective surface
bulges towards the light source.

12. Types of lenses
There are 2 types of lenses, They are :
1.Concave lens
2.Convex lens

13. Concave lens
Those which feel thinner in the middle than at the edges are
concave lenses.

14. Convex lens
Those lenses which feel thicker in the middle than at the edges are
convex lenses.

15. Prism divides white light
Take a glass prism. Allow a narrow beam of sunlight through a small
hole in the window of a dark room to fall on one face of the prism. Let
the light coming out of the other face of the prism fall on a white sheet
of paper or on a white wall. We see that the prism divides the sunlight
into seven different colours.

16. Structure of eye
We see things only when light coming from them enters our eyes.
Eye is one of our most important sense organs.
There are various parts of eye, They are :
1.Cornea 4.Retina
2.Iris 5.Lens
3.Pupil 6.Optic nerve

17. Cornea
The outer coat of the eye is white. It is tough so that it can
protect the interior of the eye from accidents. Its transparent
front part is called cornea

18. Iris
Behind the cornea, we find a dark muscular structure called iris.
In the iris, there is a small opening called the pupil. The iris is
that part of eye which gives it its distinctive colour. The iris also
controls the amount of light entering into the eye.

19. Pupil
The pupil changes size to let light into the eye. It gets smaller in
bright light and larger as the amount of light decreases. The size
of the pupil is controlled by the iris.

20. Retina
The lens focuses light on the back of the eye, on a layer called
retina . The retina contains several nerve cells.

21. Optic nerve
Sensations felt by the nerve cells are then transmitted to the brain
through the optic nerve.

22. Lens
The lens is the main part of the eye, the light entering displays on
the lens and then forms a image.

23. Tips to take care our eyes
1.If advised, use suitable spectacles.
2.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.
3.Do not look at the Sun or a powerful light directly.
4.Never rub your eyes. If particles of dust go into your eyes, wash your
eyes with clean water. If there is no improvement go to a doctor

24. Visual Defects
Some persons, including children, can be visually impaired. They
have very limited vision to see things. Some persons cannot see at
all since birth. Some persons may lose their eyesight because of a
disease or an injury.