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Light

Light is the natural agent that stimulates sight and makes things visible. Light is reflected from all surfaces. It is a form of energy.

Reflection of Light: Bouncing back of light after striking any surface such as a rough surface, Smooth surfce, shiny surface or polished surface, into the same medium, is called reflection of light. (Scroll down to continue …)

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luminous objects: Objects that give out light on their own are called luminous objects.

Examples: Flame, Sun, Glowing bulb

Non-luminous objects: Objects that do not give out light on their own are called non-luminous objects.

Examples: Rocks, Plasic Toys, Walls of room.

The Non – Luuminous objects, reflect light that falls on them.

When the reflected light enters into our eyes from the objects we could see them.

Types of Reflection:
(i) Regular Reflection: When a beam of parallel light rays is incident on a smooth and plane surface, the reflected rays will also be parallel. This type of reflection is called Regular Reflection.

The reflection from a plane mirror is an example of regular reflection.

(ii) Diffused or Irregular Reflection: When a parallel beam of light is incident upon a rough or uneven surface, it is reflected in many directions due to presence of irregularities on that.

multiple reflections: If a reflected light ray is reflected again on being incident on another surface, it is termed as multiple reflections.

Multiple reflections are used in periscope, kaleidoscope etc.

Periscopes are used in submarines, war tanks and by soldiers in bunkers to see objects.

In a kaleidoscope, beautiful patterns are formed due to multiple reflections.

Laws of reflection of light:

(i) The angle of incidence is equal to the angle of reflection.

(ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.

Lateral inversion: Lateral inversion is the effect produced by a plane mirror in reversing images from left to right.

Example: Our left hand will appear as right and vice versa.

Characteristics of the image formed by a plane mirror

Size the image formed by a plane mirror is equal to the siz of the object.

The image formed by the plane mirror is left-right inverted.

The image formed by the plane mirror erect and virtual formed behind the mirror.

Since the distance of the object in front of the mirror two mirrors inclined to each other give multiple images.

Sunlight: Sunlight, called white light, consists of seven colours.

dispersion: Splitting of light into its constituent colours is known as dispersion.

Human Eye:

A normal eye can see nearby and distant objects clearly.

Visually challenged persons can read and write using Braille system.

Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.

Parts of Human Eye:
(i) Cornea: Transparent bulge on the front surface of the eyeball which protects the eye andhelps in refraction of light.

(ii) Iris: Coloured diaphragm behind the cornea which controls the amount of light
entering the eye.

(iii) Pupil: Dark hole in the middle of iris through which light enters the eye. (iv) Eye lens: Transparent, crystalline structure behind pupil and iris. (v) Ciliary muscles: Hole the eye lens in position and control the focal length of the eye lens.

(vi) Retina: Surface of the rear part of the eyeball where the light entering the eye is focused.

(vii) Rods and Cones: Rod cells respond to the brightness of light while cone cells.