CLASS 3 SCEINCE :Understanding Light

Light

• Light is a form of energy essential for sight and warmth. Without light, Earth would be dark and cold, making life impossible.
• Light enables vision and warmth. Without light, proper vision and functioning are impossible.
• Light sources include the Sun, candles, torches, electric bulbs, and more.
• Fireflies, insects, produce their own light. Historically, the Chinese used fireflies in containers as lanterns.
• Luminous objects emit their own light (e.g., Sun, electric bulb, lamp, torch).
• Non-luminous objects do not produce light; they reflect it (e.g., book, table).
• Light emitted by a light source makes objects visible. Light reflected off objects enters our eyes, enabling us to see.
• Light travels in a straight line.
• Light from reflecting objects falls on our eyes, enabling us to see them. This reflection of light lets us see.
• Non-luminous objects are invisible in the dark because light isn't being reflected off them.
• To see, light must strike an object, be reflected, and enter the eye.
• Shadows are formed when an opaque object blocks light, creating the area where light cannot reach.
• Mirrors reflect light, enabling us to see reflections — an example of light reflection.
• Light sources create their own light. The Sun and stars, along with lightning, are natural light sources. Torches, candles, fireworks, lamps, and electric lights are man-made sources.
• Light from a source helps us see the source itself.
• Sunlight helps us see during the day.
• Artificial light sources are needed for seeing at night or in the absence of sunlight.
• Sources of light are categorized as natural (Sun, lightning, fireflies, stars) or man-made (torches, candles, fireworks, lamps, electric lights).
• A day without sunlight would make the Earth dark and cold, making survival impossible. Light is essential for vision and warmth.
• Besides the sun, candles, torches, and electric bulbs are light sources.

How We See Things

• Light travels in a straight line.
• Light reflected from objects travels into our eyes, enabling us to see them.
• Mirrors reflect light, enabling us to see reflections.
• Light that bounces off an object into our eyes lets us see that object.
• Non-luminous objects are visible only when light falls on them, bounces off, and enters our eyes.
• We cannot see non-luminous objects in the dark.
• To see, light must fall on an object, reflect off it, and enter the eye.
• Light reflects off objects, entering our eyes, and enabling us to see them.
• Light from a source helps us see the source.
• We can easily see a candle when its light falls on our eyes.
• Light from a candle or the Sun falling on our eyes helps us see these objects.
• We cannot see non-luminous things in the dark. We can see them only when light falls on them and bounces off into our eyes.
• Reflection of light allows us to see objects or our faces in mirrors.
• Light from a source bounces off objects and enters our eyes.

Types of Objects

• Transparent objects allow light to pass straight through completely (e.g., glass, air, water, some plastics).
• Translucent objects allow some light to pass through but scatter it (e.g., frosted glass, waxed paper, dirty water, some plastics).
• Opaque objects do not allow light to pass through them (e.g., a pillow, wall, table, wooden door). These categories are determined by how much light passes through the object.

Shadows

• Shadows are formed when an opaque object blocks light entirely or partially.
• Shadows always appear on the opposite side of the light source.
• Shadows are dark.
• The length of a shadow changes throughout the day (longer in the morning/evening, shorter at noon).
• An opaque object blocks light, creating a shadow.
• The shadow's length indicates the time of day, the sun's position.
• Shadows exist only when there is light and an opaque object.
• Shadows are the dark areas where light cannot reach.
• They are always on the opposite side of the object to the light source, and are dark in colour.
• Shadows form when light is blocked.
• Shadows are formed only when there is a light source and an opaque object to block its path.
• Shadows are always dark.
• Shadows are always formed on the side opposite to the light source.
• The length of a shadow indicates the time of day.

Sources of Light

• Natural sources: Sun, lightning, fireflies, stars.
• Man-made sources: torches, candles, fireworks, lamps, electric lights (bulbs, tube lights), lanterns.
• Light sources produce their own light.

Letting Light Through

• Objects are classified into three categories based on how much light passes through them: transparent, translucent, and opaque.
• Transparent objects allow light to pass straight through (e.g., glass, air, water). This is how we see clearly through certain materials.
• Translucent objects allow some light to pass through but scatter it (e.g., frosted glass, waxed paper, butter paper, dirty water, some plastics). This is why some materials allow some light through and other materials do not allow any light through.
• Opaque objects do not allow any light to pass through (e.g., pillows, walls). The materials do not let any light through them when light hits the object.
• Light can pass through some materials but not others. This leads to the classification of different materials as transparent, translucent, and opaque.

Additional Information

• Objects that give off their own light are called luminous objects (e.g., the Sun, a light bulb).
• Objects that do not emit light but reflect it are called non-luminous objects (e.g., a book, a table).
• We can see non-luminous objects only when light reflects off them and enters our eyes.
• Mirrors reflect light, enabling us to see reflections.
• Mirrors and diamonds do not produce light but shine because they reflect light.
• We can see our faces in a mirror due to the reflection of light from our faces onto the mirror and then into our eyes.
• Light from a source helps us see.
• Light bouncing off objects is reflected light.
• Shadows are formed when light is blocked.
• Shadows' length indicates the time of day.
• The position of the sun affects the length of the shadow.
• The Sun is a natural light source.
• Electric bulbs and candles are examples of man-made light sources.
• Fireflies are a natural light source.
• The Chinese used fireflies as ancient lanterns.