Meera was playing in the school ground during the afternoon. She noticed that her shadow was very short and fell just below her feet. In the evening, when she walked home, her shadow became very long and stretched far behind her.
"Why does my shadow keep changing?" she asked her teacher. Her teacher smiled and said, "It is all about light and how it travels!" Let us find out how light creates shadows and why they change.
What is Light?
Light is a form of energy that helps us see things around us. Without light, everything would be dark. Light always travels in a straight line.
Sources of Light
Objects that give out their own light are called luminous objects. Sources of light can be grouped into two types:
1. Natural sources: The Sun is the biggest natural source of light on Earth. Stars, lightning and fireflies are also natural sources of light.
2. Artificial sources: These are made by humans. Examples include electric bulbs, tube lights, candles, oil lamps (diyas lit during Diwali) and torches.
Types of Objects Based on Light
When light falls on an object, three things can happen:
Transparent objects allow all light to pass through them. You can see clearly through them. Examples: clear glass, clean water, air.
Translucent objects allow only some light to pass through. You can see things through them, but not clearly. Examples: frosted glass, oiled paper, thin cloth.
Opaque objects do not allow any light to pass through them. You cannot see through them at all. Examples: a wooden door, a brick wall, a metal plate, your body.
How Are Shadows Formed?
When light falls on an opaque object, the object blocks the light. The area behind the object where light cannot reach becomes dark. This dark area is called a shadow. Three things are needed to form a shadow: a source of light, an opaque object, and a screen (surface where the shadow falls).
Shadows Change During the Day
The Sun moves across the sky from east to west during the day. As the position of the Sun changes, the length and direction of shadows also change.
Morning: The Sun is low in the east. Shadows are long and point towards the west.
Noon: The Sun is high overhead. Shadows are very short and fall just below the object.
Evening: The Sun is low in the west. Shadows are long again and point towards the east.
Shadow Puppets -- A Traditional Art
In many parts of India, especially in Andhra Pradesh, Karnataka and Kerala, artists perform shadow puppet shows (called Tholpavakoothu in Kerala and Tholu Bommalata in Andhra Pradesh). They hold flat puppets made of leather between a light source and a white screen. The shadows of the puppets tell stories from the Ramayana and Mahabharata.
Arjun placed different objects in front of a torch and observed what happened:
A glass tumbler -- light passed through completely -- Transparent
A sheet of paper oiled with ghee -- some light passed through -- Translucent
A steel thali -- no light passed through -- Opaque
Priya held a book between a table lamp and the wall. A dark patch appeared on the wall in the shape of the book. This dark patch is the shadow. When she moved the book closer to the lamp, the shadow became bigger. When she moved it farther from the lamp, the shadow became smaller.
Ravi planted a stick in the school garden at 8 AM, 12 noon and 4 PM and traced its shadow each time. At 8 AM the shadow was long and pointed west. At noon it was very short. At 4 PM it was long again but pointed east.
| Word | Meaning |
|---|---|
| Luminous | An object that gives out its own light (e.g., Sun, bulb) |
| Transparent | Allows all light to pass through; objects behind are clearly visible |
| Translucent | Allows some light to pass through; objects behind are not clearly visible |
| Opaque | Does not allow any light to pass through |
| Shadow | A dark area formed when an opaque object blocks light |
| Sundial | An ancient device that uses the shadow of a stick to tell time |
Finished learning? Now test what you know!