Science Class 7 - Light Notes

Light

Welcome to the chapter on Light for Class 7. In this chapter, you will learn about the nature of light, how it travels, how it interacts with objects, and its importance in our daily life. By the end of this chapter, you will understand concepts like reflection, refraction, and the formation of shadows!

Introduction

Light is a form of energy that enables us to see the world around us. The Sun is the main source of natural light. We also use artificial sources like bulbs and lamps.

How Does Light Travel?

• Light travels in a straight line.
• This is called the rectilinear propagation of light.
• We can see this when sunlight passes through a small hole or when a torch beam is visible in the dark.

Reflection of Light

When light hits a shiny surface, it bounces back. This is called reflection.

• Mirrors reflect light and help us see our image.
• Smooth surfaces reflect light better than rough surfaces.

Refraction of Light

When light passes from one medium to another (like air to water), it bends. This is called refraction.

• A pencil in a glass of water looks bent due to refraction.
• Refraction helps us see objects underwater.

Formation of Shadows

Shadows are formed when an object blocks the path of light.

• Opaque objects form dark shadows.
• Transparent objects do not form shadows.
• Translucent objects form faint shadows.

Uses of Light

• Helps us see things around us.
• Plants use sunlight to make food (photosynthesis).
• Used in communication (fiber optics).
• Used in medical instruments and technology.

Fun Activity: Shadow Play!

Use a torch and your hand to make different shadow shapes on the wall. Notice how the shadow changes when you move your hand closer or farther from the light.

Summary

• Light travels in a straight line.
• Reflection and refraction are important properties of light.
• Shadows are formed when light is blocked by an object.
• Light is essential for life and technology.

Practice Questions

1. What is the main source of natural light?
2. What happens when light hits a mirror?
3. Why does a pencil look bent in water?
4. What kind of objects form shadows?
5. Name two uses of light in daily life.

Challenge Yourself

• Draw a diagram showing the reflection of light from a mirror.
• List three devices that use light.

Did You Know?

• Light from the Sun takes about 8 minutes to reach Earth!
• Rainbows are formed due to the refraction and reflection of sunlight in water droplets.

Glossary

• Reflection: Bouncing back of light from a surface.
• Refraction: Bending of light when it passes from one medium to another.
• Opaque: Objects that do not let light pass through.
• Transparent: Objects that let light pass through easily.
• Translucent: Objects that let some light pass through.

Answers to Practice Questions

1. The Sun.
2. It is reflected (bounces back).
3. Because of refraction.
4. Opaque objects.
5. Seeing, photosynthesis, communication, medical uses (any two).

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Explore the world of light and discover how it helps us every day!