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Name – Butani Jay H.Class – VIII – BRoll No – 17Subject – ScienceTopic – Light

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4WHAT IS LIGHT ?Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.

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LATERAL INVERSIONFor Example You are the object and what you see in mirror is your image. You are identical to your image as seen in the mirror. In case of a plane mirror the image formed is erect and same size as the object. But there is one difference is in your left and right. When you move your right hand, in the image it seems as if your left hand is moving. This is called lateral inversion, where left appear be right and right appears to be left.

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REFLECTING THROUGH SPHERICAL MIRRORS

If the reflecting surface of a spherical mirror is concave, it is called as a concave mirror. If the reflecting surface of a spherical mirror is convex, it is called a convex mirror.

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USES OF SPHERICAL MIRRORSConvex mirrorConcave mirror

Convex mirror

Convex are mainly use at rear side of a car on driver’s side of a car is a convex mirror. In some countries, these are labelled with safety warning , to warm the driver of the convex mirror’s distorting effects on actual distance of the vehicle behind the driver

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Concavemirror

1. Doctors use concave mirror for examining eyes , ears, nose and

throat.2. Concave mirrors are also

used by dentists to see an enlarged image of

teeth.3. The reflectors of torches,

headlights of cars and scooters are concave in

shape.

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LAWS OF REFLECTION•Incident ray – The light ray falling on any surface is called the incident ray.•Reflected ray- The light ray that comes back after reflection is called the reflected ray.•Normal ray – The line perpendicular to the reflecting surface is called the normal ray.•Angle of incidence – The angle between the incident ray and the normal ray is called the angle of incidence.•Angle of reflection – the angle between the reflected ray and the normal ray is called the angle of reflection.

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REGULAR AND IRREGULAR REFLECTION

The Laws of reflection are valid for reflection from all shiny surfaces. Thus the angle of incidence has to be equal to the angle of reflection in each case. It is just that the rays reflected from an irregular surface are unparallel rays. When the rays reflected from a plane surfaces are not parallel, the reflection is known irregular reflection.

irregular reflection

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regular reflection

On the other hand, reflection of light rays from a smooth surface like that of a plane mirror is called a regular reflection Images formed by regular reflection.

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MULTIPLE REFLECTIONSTo predict the path of incident rays for this

case, we need to apply the laws of reflection

again. However, at the same time, understand that when two mirrors are placed at an angle

the rays of light are reflected multiple times

through them. For instance, when two

mirrors are set parallel facing each other they will create the illusion that the image of the

object repeats forever.

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KALEIDOSCOPE – AN ILLUSTRATION OF MULTIPLE REFLECTION

The kaleidoscope also uses multiple reflections through mirrors to form beautiful patterns.

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SUNLIGHT AND ITS COLOURS

• The seven colours are violet, indigo, blue, green, yellow, orange and red. All this spectrum of colours we can perform this simple activity.

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THE HUMAN EYEThe human eye a sense organ. It helps in seeing

different objects. The light reflected from different objects enter our eyes and thus we can see things around us. It is an important organ. So, understandings its structure is also very

important.

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The human eye has a nearly spherical shape, and is about an inch in diameter. The white portion visible from outside is the cornea. Behind the cornea is a space filled with a liquid known as aqueous humour. Further behind is a crystalline lens. Between the aqueous humour and the lens is the iris, a muscular diaphragm which has a small hole in it known as the pupil. The pupil usually appears black, and controls the amount of light entering the eye.

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ACCOMODATION OF THE EYE The eye focuses on different

objects by changing the radius of curvature of the lens. The cilliary muscles relax to view distant objects and contract to focus on nearby objects. This is knows as the power of accommodation of the eye. However, the muscles cannot be strained beyond a limit and hence if the

objects is placed too close to your eyes the image formed on the retina would be blurred

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PERSISTENCE OF VISION The image of an object

formed in retina does not vanish immediately; it stays for 1/16 second. This is called as the persistence of vision. Any image that is flashed more than 16 images per second would be seen as moving.

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DEFFECTS OF THE HUMAN EYE

At times, the eye lens cannot focus even when the objects is placed beyond 25cm. Some people cannot see nearby objects clearly and see nearby objects clearly and see distant objects clearly. This defect ;is called hypermetropia. There are also people who can see nearby objects clearly but face a problem viewing far-off objects. This defect is called myopia. Thus for such cases the eye lens has to be corrected using other lenses, and the doctor asks you to wear spectacles.

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CARE OF YOUR EYES• You should have regular checkup

for your eyes. If there is any problem, you should go to an eye specialist. If advised, use suitable spectacles.

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• Never look directly into a very bright source of light, like the sun. It can damage the retina of the eye.

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• Never rub your eyes if some particles dust go into your eyes, wash your eyes with clean water. In case there is no improvement, visit a doctor.

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• 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. Always read under proper light.

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• Do not read in a moving vehicle.• Avoid watching television or working

on the computer for long sessions always take a break to rest your eyes.

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SCRIPT FOR THE VISUALLY CHALLENGED: THE BRAILLE SYSTEM

• The Braille system is a method that is widely used by visually challenged people to read and write. It was devised in 1821 by Louis Braille, a blind Frenchmen. Visually challenged people feel the dots to identify the character written in Braille system.

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