EVS / Science -- Class 4

Topic: Light and Shadow
Name: ____________________________Class: 4Date: ________________
Learning Objectives
Let Us Begin!

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.

Step-by-Step Explanation

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.

Think about it: During a power cut at home, what sources of light does your family use?

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.

Think about it: Is the glass window of your classroom transparent or translucent? What about a curtain?

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.

Think about it: In ancient India, people used a sundial (called Dhoop Ghadi) to tell the time by looking at the shadow of a stick. How do you think this worked?

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.

Key Words
WordMeaning
LuminousAn object that gives out its own light (e.g., Sun, bulb)
TransparentAllows all light to pass through; objects behind are clearly visible
TranslucentAllows some light to pass through; objects behind are not clearly visible
OpaqueDoes not allow any light to pass through
ShadowA dark area formed when an opaque object blocks light
SundialAn ancient device that uses the shadow of a stick to tell time

EVS / Science -- Class 4 (continued)

Topic: Light and Shadow -- Examples and Practice
Examples
Example 1: Classifying Objects

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

Example 2: Shadow Formation

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.

Example 3: Shadows at Different Times

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.

Key Points to Remember
Practice Questions

A. Fill in the Blanks

  1. Light always travels in a line.
  2. Objects that give out their own light are called objects.
  3. A glass window is an example of a object.
  4. A shadow is formed when an object blocks light.
  5. At noon, shadows are because the Sun is directly overhead.

B. Multiple Choice Questions

  1. Which of the following is a natural source of light?
    (a) Candle(b) Torch(c) Sun(d) Tube light
  2. Frosted glass is an example of a:
    (a) Transparent object(b) Translucent object(c) Opaque object(d) Luminous object
  3. Shadows are longest during:
    (a) Noon(b) Morning and evening(c) Midnight(d) Afternoon

C. Short Answer Questions

  1. Name two natural and two artificial sources of light.
  2. What three things are needed to form a shadow?
  3. Why does a shadow not form behind a glass window?
  4. Why are shadows short at noon and long in the morning?
Think and Do -- Fun Activity: Shadow Tracing

What you need: A stick or pencil, a sunny spot in your school ground, chalk and a clock.

What to do: Fix the stick upright in the ground. At 9 AM, trace the shadow with chalk and write the time. Repeat at 11 AM, 1 PM and 3 PM.

Record your observations below:

TimeShadow Length (approx.)Direction of Shadow
9:00 AM
11:00 AM
1:00 PM
3:00 PM

What did you notice about the shadow as the day went on?