Class 8 Light Notes
Class 8 Light Notes
Light:-
Light is a form of energy that produces sensation of vision in our eyes.
Reflection of Light:-
The phenomenon of bouncing back of a ray of light after striking on a highly polished (reflecting) surface is called reflection of light.
Incident ray:- The light ray, which strikes any surface, is called the incident ray.
Reflected ray:- The ray that comes back from the surface after reflection is known as the reflected ray
Angle of incidence (∠i):- The angle between the normal and incident ray is
called the angle of incidence.
Angle of reflection (∠r):- The angle between the normal and the
reflected ray is known as the angle of reflection.
![reflection of light](https://brainigniter.in/wp-content/uploads/2020/04/Laws-of-reflection-1024x473-1.png)
Laws of Reflection:-
- First law:- The angle of incidence is equal to the angle of reflection. i.e., ∠i = ∠r
- Second Law:- The incident ray, the normal at the point of incidence and the reflected ray, all lie in the same plane.
Lateral Inversion:-
The phenomenon of left side appearing right side and right side appearing left side in the image formed by a mirror is called lateral inversion.
Regular Reflection:-
The reflection from a smooth surface such that all the parallel rays reflected are also parallel is called regular reflection.
![Regular Reflection](https://brainigniter.in/wp-content/uploads/2020/08/regular-reflection.png)
Irregular/Diffused Reflection:-
The reflection from an irregular surface such that all the parallel rays reflected are not parallel is called irregular or diffused reflection.
![Irregular Reflection](https://brainigniter.in/wp-content/uploads/2020/08/irregular-reflection-1.jpg)
- Images are formed by regular reflection.
- Reflected light can be reflected again.
- The devices based on multiple reflection of light are periscope and kaleidoscope.
- Periscopes are used in submarines, tanks and also by soldiers in bunkers to see things outside.
- Kaleidoscopes are used by designers of wallpapers and fabrics and artists to get ideas for new patterns.
- Sunlight is referred to as white light that consists of seven colours i.e., violet, indigo, blue, green, yellow, orange and red.
Refraction of Light:-
The phenomenon of bending of a ray of light when it passes from one medium to another medium is called refraction of light .
- In going from rarer to denser medium, the ray of light bends towards normal and in going from denser to rarer medium, the ray of light bends away from normal.
![](https://brainigniter.in/wp-content/uploads/2020/08/refraction-of-light.jpg)
Human Eye:-
![human eye](https://brainigniter.in/wp-content/uploads/2020/05/class-10-human-eye.jpg)
- Human eye ball is approximately spherical in shape with diameter of about 2.3 cm.
- Light enters the eye through a thin membrane called the cornea.
- Iris controls the size of pupil.
- Pupil regulates the amount of light entering the eye.
- Image is formed on retina & its nature is real & inverted.
- The retina has two types of light sensitives cells i.e., rods & cones.
- Rods are responsible for vision at low light.
- Cones are active at higher light levels & is responsible for colour vision.
- Ciliary muscles help to change the focal length of the eye lens.
Blind spot:- The junction of retina and optic nerve where no light sensitive cells are present is called blind spot.
- Vision is not possible at blind spot.
Persistence of vision:- The effect of an image stays on retina for about 1/16 of a second even after the object is removed. This is called persistence of vision.
Care of Eyes:-
Some tips to take care of the eyes are as follows:-
- Do not look at the sun or a powerful light directly.
- If advised, 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.
- 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.
- Wash your eyes frequently with clean water.
- Always read at the normal distance for vision. Do not read by bringing your book too close to your eyes or keeping it too far.
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