Light - Class 6 Notes & Olympiad Questions

Light

Light is a type of energy that allows us to see objects and surroundings. It is a fundamental component of our visual perception.
It comes from sources like the sun, light bulbs, or even a burning candle. When light reaches our eyes, it allows us to perceive objects and colours.

Sources of Light

Objects that emit or give out light are called sources of light. There are two main sources of light: Natural and artificial.

Natural Sources

These are objects in nature that emit their own light.

a) The Sun: The most significant natural source of light, which emits light and heat energy.
b) Stars: These are distant suns that emit light and appear as points of light in the night sky.
c) Fireflies: Small insects that produce light through a chemical reaction in their bodies.

Artificial Sources

These are objects created by humans that emit light.

a) Light bulbs: Electric bulbs that produce light when an electric current passes through them.
b) Flashlights: Portable devices that produce light using batteries and a bulb.
c) Candles: Flames of burning wax that emit light and heat.

Luminous Objects and Non-luminous Objects

Luminous objects are those that emit light of their own, such as the sun, stars, fireflies, and glow worms. On the other hand, non-luminous objects do not emit light but can be seen when they reflect light from a luminous object. Examples of non-luminous objects include chairs, tables, books, flowers, and roads.

Differences between Luminous and Non-Luminous Objects

Transparent Objects, Translucent Objects, and Opaque Objects

Objects differ in their ability to transmit light. They can be divided into transparent, translucent and opaque based on these differences.

Propagation of Light

a) Propagation of light refers to the way light travels from its source to reach our eyes or other objects.
b) Light travels in a straight line until it encounters an obstacle or is reflected or refracted by a material. This is known as rectilinear propagation of light.
c) Just like when we throw a ball in a straight line and it keeps going until something stops it, light also travels in a straight line until it hits something.
d) The rectilinear propagation of light explains how shadows are formed and also image formation in a pinhole camera.

Rays of Light: A ray of light is a straight, thin path along which light travels. Think of a ray of light as an arrow that shows the direction in which the light is moving.

A collection of rays along a specific direction is called a beam of light.

Pinhole Camera

a) A pinhole camera uses the rectilinear propagation of light to create an inverted image of objects on a screen.
b) A pinhole camera is a special type of camera that forms an image of objects on a screen. It's like a closed box with a small hole in it. When light enters through the tiny hole, it creates an upside-down image on the screen inside the box.
c) In a pinhole camera, the small hole acts like a lens, allowing light rays to enter the camera. The rays of light from different parts of an object pass through the hole and form an image on the screen inside the camera. The image appears upside down because of the way light travels in straight lines.
d) The size of the image formed is smaller than the actual object, and it's a real image, which means you can project it onto a surface and see it clearly.
e) The smaller the pinhole, the sharper the image will be, but it will also be dimmer. If the hole is too large, the image will be blurry.