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๐ฌ Think about it
On a sunny day, your dark shadow copies your every move. Where does it come from? And why can you not catch it? The secret is simple: light travels straight and your body blocks it. Let us explore shadows.
How is a shadow formed?
- Light travels in a straight line.
- An opaque object placed in its path blocks the light.
- The dark patch where light does not reach is the shadow.
- We need a light source, an opaque object, and a screen.
Example:
Standing in the Sun, your body blocks the light and a dark shadow falls on the ground behind you.
How a Shadow Forms
Light travels in a straight line
↓
Object blocks light
An opaque object comes in the path of the light.
↓
Light is stopped
Light cannot reach the area behind the object.
↓
A dark patch (shadow) forms on the screen
What do shadows depend on?
- Opaque objects form darker shadows.
- Translucent objects make lighter shadows.
- Some transparent objects make faint shadows.
- Shape, size, and sharpness depend on the object's position.
Example:
Changing the colour of an opaque object does not change the colour of its shadow.
In this Activity, we will change parts of a shadow set-up to learn what a shadow needs.
Materials needed
Opaque objects of different shapes and sizes, a torch, and a screen.
Procedure
1. Collect opaque objects of different shapes and sizes.
2. Set up the torch, object, and screen as in Activity 11.3.
3. Carry out each action listed in the first column of Table 11.2.
4. Observe the shape and size of the shadow each time.
5. Record your observations in the second column of Table 11.2.
2. Set up the torch, object, and screen as in Activity 11.3.
3. Carry out each action listed in the first column of Table 11.2.
4. Observe the shape and size of the shadow each time.
5. Record your observations in the second column of Table 11.2.
Table 11.2 — Observation of shadows
| Action | Observations regarding shadow |
|---|---|
| The screen is removed. | No shadow is seen. |
| The object is removed. | No shadow is seen. |
| The torch is switched off. | No shadow is seen. |
| The colour of the object is changed. | Shadow stays dark, colour does not change. |
| The object is moved closer to the screen, keeping the torch and the screen fixed. | The shadow becomes smaller and sharper. |
| The object is moved closer to the torch, keeping the torch and the screen fixed. | The shadow becomes larger. |
| The object is tilted, keeping the torch and the screen fixed. | The shape of the shadow changes. |
Observation
No shadow forms if the screen, object, or torch is missing. The shadow's size and shape change with the object's position, but its colour stays dark.
Explanation
A shadow needs a light source, an opaque object, and a screen. So removing any one means no shadow forms.
โ Summary
- Three things needed
- Remove one, no shadow
- Position changes size
- Colour stays dark
๐ญ Fascinating Facts
- Shadow play, or shadow puppetry, is centuries old in India.
- Flat cut-out puppets are placed between a light and a screen.
- Moving the puppets and light brings the characters to life.
- Styles include Tholu Bommalata, Ravana Chhaya, and Tholpavakoothu.
Important Points
- A shadow needs light, an opaque object, and a screen.
- The object's position changes the shadow's size and shape.
- Changing the object's colour does not change the shadow's colour.
โ Test Yourself
-
What three things are needed for a shadow?
View Answer
A light source, an opaque object, and a screen. -
What is a shadow?
View Answer
The dark patch formed where light is blocked by an object. -
Does the shadow's colour change with the object's colour?
View Answer
No, the shadow stays dark. -
What happens to the shadow as the object nears the torch?
View Answer
The shadow becomes larger. -
Which objects form the darkest shadows?
View Answer
Opaque objects.
Important Definitions
- Shadow — the dark patch formed when an opaque object blocks light from reaching a screen.
๐ NCERT Question 4 — Look at the images
Look at the images shown in Fig. 11.17 and select the correct image showing the shadow formation of the boy.
View Answer →
๐ NCERT Question 5 — The shadow of a
The shadow of a ball is formed on a wall by placing the ball in front of a fixed torch. Choose the most accurate representation.
View Answer →
๐ NCERT Question 6 — Based on Fig. 11.18,
Based on Fig. 11.18, match the position of the torch in Column A with the characteristics of the ball's shadow in Column B.
View Answer →
