Light Chapter Notes | Science Class 4 ICSE PDF Download

Introduction

Luminous and Non-luminous Objects

• Luminous objects produce their own light.
• Examples include the sun, stars, torch, bulb, candle, and lamp.
• Some luminous objects, like the sun and stars, are natural, while others, like torches and lamps, are man-made.
• Most luminous objects, such as the sun, stars, and candle flames, also produce heat along with light.
• Non-luminous objects do not produce light but reflect light from luminous objects.
• Examples of non-luminous objects include the moon, trees, chairs, tables, glass, and pencils.
• Non-luminous objects become visible only when light shines on them.

Sources of Light

• Natural sources produce light on their own without human intervention.
• The sun is the primary natural source of light and is vital for all living things.
• Stars produce light, but only a small amount reaches Earth due to their vast distance.
• The moon reflects sunlight and does not produce its own light.
• Some organisms, like fireflies, jellyfish, and glow-worms, can also produce light naturally.

Artificial Sources of Light

• Artificial sources are human-made devices that produce light.
• Examples include electric bulbs, tube lights, torches, lamps, candles, and laser lights.

Properties of Light

• Light travels in straight lines as rays.
•  Light travels very fast, at the speed of 3 x 10⁸ m/s (metre per second).
• Light spreads in all directions from its source.
• Light can travel through empty space, known as a vacuum.
• Light can be reflected, meaning it bounces back when it hits a surface, making objects visible when the reflected light reaches our eyes.
• Light can be refracted, or bent, when it passes through materials like water, air, or glass, causing a slight change in direction.
• Refraction causes objects, like a straw in water, to appear bent at the surface.
• When light passes through a glass prism, it splits into seven colors: violet, indigo, blue, green, yellow, orange, and red (remembered as VIBGYOR).

Transparent, Translucent, and Opaque Materials

• Materials interact with light differently based on how much light they allow to pass through.
• Materials are classified into transparent, translucent, and opaque based on their light-passing ability.

Transparent Materials

• Transparent materials allow light to pass through easily.
• Examples include air, clear water, glass, clear plastic, and crystal.

Translucent Materials

• Translucent materials allow only a small amount of light to pass through.
• Examples include butter paper, colored plastic, tissue paper, frosted glass, thin cloth, and sunglasses.
• These materials can be colorless or lightly colored.

Opaque Materials

• Opaque materials block all light from passing through.
• Examples include wood, metal, books, cardboard, walls, the human body, and stones.

Formation of Shadows

• Shadows form when an object blocks light traveling in a straight line.
• A dark shape, called a shadow, appears on the surface opposite the light source.
• Only opaque or translucent objects can form shadows.
• Opaque objects create dark shadows, while translucent objects create faint shadows.
• Transparent objects do not form shadows because light passes through them completely.
• Shadows always appear black or dark, regardless of the object’s color.
• Shadows can be larger or smaller than the object, depending on the light source’s position.
• The length of a shadow changes during the day due to the sun’s position.
• Shadows are longest in the morning and evening and shortest at midday when the sun is directly overhead.

Terms to Know

• Luminous objects: Objects that produce their own light.
• Non-luminous objects: Objects that reflect light from luminous objects.
• Vacuum: Empty space where light can travel.
• Reflection: When light hits a surface and bounces back.
• Refraction: When light bends slightly as it passes through a different material.
• Transparent: Materials that allow light to pass through easily.
• Translucent: Materials that allow only a small amount of light to pass through.
• Opaque: Materials that block all light from passing through.