What is Light? How light help us see objects? - Learning Concepts
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Light

Concept: Properties and Sources of Light and the Human Eye

Light is a form of energy that enables us to see things around us. When light falls on any object, it gets reflected and reaches our eyes, making a thing visible.

Properties of light:

  • Light travels in a straight line.
  • Light gets reflected when it strikes a reflecting surface.
  • Light rays change direction.
  • The speed of light in vacuum is 3 x 108 metre/second.
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Sources of light:

Light is emitted by both natural and man-made objects. Based on the ability to emit light, objects can be classified as follows—

  • Luminous objects: The object which can emit their own light are called luminous objects.
  • Examples: Sun, candle, bulb, CFL light, stars etc.

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  • Non-luminous objects: The objects which cannot emit light are called non-luminous objects.
  • Examples: Wood, charcoal, Moon, chalk, cotton cushion etc.

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Permeability towards light:

The ability of an object to allow light rays to pass through it is called permeability towards light. Based on this property, objects can be classified as follows—

  • Transparent objects: The objects that allow light to pass through them completely are called transparent objects.
  • Examples: Glass, water, air.

  • Translucent objects: The objects that allow light to pass through them partially are called translucent objects.
  • Examples: Butter paper, plastic sheet, ground glass.

  • Opaque objects: The objects that do not allow light to pass through them at all are called opaque objects.
  • Examples: Wood, plastic, brick.

Translucent object

Opaque object

Reflection of light:

  • When light falls on a smooth and shiny or opaque surface, it bounces back instead of passing through it. This returning of light rays to the same medium is called reflection of light.
  • Substances with shiny surfaces like painted glass, metal sheets, mirror etc. are good reflectors.
  • Opaque objects like charcoal, plastic, wood are good absorbers of light.
  • There are various advantages of reflection of light—
    1. The reflection of light enables us to see objects around us.
    2. It helps us to see our image in the mirror.
    3. This property of light is used in a microscope to study tiny specimens.

Laws of reflection:

The laws of reflection state that—

  • The incident ray, the normal and the reflected ray lie on the same plane.
  • The angle of incidence is equal to the angle of reflection.
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  • The light ray falling on a reflecting surface from a source of light is called an incident ray.
  • The light ray which bounces back after touching the reflecting surface is called a reflected ray.
  • A line running between the incident ray and the reflected ray perpendicular to the reflecting surface is called the normal.
  • The angle between the incident ray and the normal is called the angle of incidence.
  • The angle between the normal and the reflected ray is called the angle of reflection.

Human eye:

The human eye is a sense organ specialized for accepting the visual images interpreted by the brain.

It enables us to do the following things—

  • See the objects around us.
  • Differentiate the colours.

There are six muscles that ensure the proper functioning of our eyes.

Part of the eye Function
Pupil: It is a small opening located in the centre of the iris. To regulate the amount of light entering the eye.
Sclera:It is a white protective layer covering the outside of the eye. It is a white protective layer covering the outside of the eye.
Iris:The colour of the iris imparts colour to the eye. It is a ring-like structure present behind the cornea. Controls the amount of light entering the eye by regulating the opening and closing of the pupil.
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Cornea: The transparent outer layer at the front of the eye. Nature-1 Helps to focus on the light so that one can see clearly.
Retina: It is the layer found at the back of the eye. It contains nerve tissue that senses light and sends visual images to the brain. Rod and cone cells are located on the retina, which is sensitive to light and colour intensity, respectively. Nature-1 Image formation in the eye takes place in the retina.The visual signals received are converted into electrical impulses, which are then sent to the brain.
Eye lens: It is the transparent structure located behind the iris and in front of the vitreous humour. The lens in our eyes is converging and so is also called a convex lens. To create an image by focussing on the light rays entering the eye.
Ciliary muscles: These muscles are attached to the eye lens on both sides. To regulate the size of the eye lens by stretching and relaxing.
Blind spot: It is a specific point where optic nerves and retina come together. There are no photoreceptor cells located in this region. Hence, no vision is possible here.
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Aqueous humour: It is a transparent fluid between the cornea and the front region of the vitreous humour. It nourishes the lens, keeps it moist and maintains the required pressure in the eye.
Vitreous humour: It is a gel-like substance that occupies the space between the lens and retina. It is responsible for maintaining the round shape of the eye and keeping the eye clear.
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New Words

Vacuum: A space where there is no air.

Microscope: A device used to observe things that are not visible to the naked eye.

Photoreceptor cells: The cells which respond to light.

Pigmented: Something that is coloured.


Did You Know?

  • Light is made up of several colours.
  • Some objects appear in some colours. They reflect specific colours of white light and absorb the other colours. The light reflected to the eye is the colour that we are able to see.
  • The light bulb was invented by famous scientist Thomas Edison.
  • Light travels faster than sound, and so, one can see lightning before hearing the thunder.
  • Some animals cannot bear high-intensity light and hence come out only in the absence of light. These animals are called nocturnal animals, like owls, bats.
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