At Bodhiclasses, we believe that learning should be a beautiful journey—one that inspires curiosity, creativity, and clarity. Whether you’re revising for your exams or just want to explore the wonders of science, we’re here to walk with you every step of the way. Light is something we see every day, but how often do we stop and truly understand its behavior? In this chapter 11 of Class 7 NCERT Science textbook: Light – Shadows and Reflection, we dive into the fascinating world of light—how it travels, interacts with objects, and helps us see the world around us.
🔆 Sources of Light: Natural and Artificial
The chapter begins with a simple classification of light sources:
- Luminous objects are those that emit their own light, such as the Sun, stars, lightning, fireflies, and electric bulbs.
- Non-luminous objects don’t produce their own light; they reflect light from other sources. The Moon, for instance, only appears to shine because it reflects sunlight.
Humans have created artificial lighting sources over time—from fire torches to modern LEDs, which are energy-efficient and environmentally friendly.
🚦 Does Light Travel in a Straight Line?
Yes! Through activities involving matchboxes and pipes, students observe that light travels in straight lines. This principle explains many everyday phenomena, like why shadows form behind objects or why we cannot see around corners without mirrors.
🌫️ Transparent, Translucent, and Opaque Materials
This section helps classify materials based on how much light passes through them:
- Transparent: Allow almost all light through (e.g., glass).
- Translucent: Allow partial light through (e.g., tracing paper).
- Opaque: Block all light (e.g., wood, cardboard).
Each type of material affects how we see objects and how shadows are formed.
🌑 Understanding Shadows
A shadow forms when an opaque object blocks light. Key insights include:
- Opaque objects form dark shadows.
- Translucent objects form light shadows.
- Transparent objects form faint shadows.
Shadows depend on the position of the light source, object, and screen. Interestingly, shadows do not carry the color of the object—they’re always dark.
🔍 Reflection of Light
Reflection is the bouncing back of light from shiny surfaces like mirrors. Activities in this chapter show how mirrors can redirect light. This is the principle behind seeing your face in a mirror or using mirrors to light up a dark spot.
🪞 Images in a Plane Mirror
Looking into a mirror reveals fascinating properties:
- The image is same in size and upright.
- It is laterally inverted (left appears right).
- It cannot be captured on a screen (it’s a virtual image).
- The distance of the image from the mirror is equal to the object’s distance.
This is why the word “AMBULANCE” is written in reverse on vehicles—it appears correctly in a driver’s mirror!
📷 Pinhole Camera
This simple device demonstrates how light travels in straight lines:
- It forms a real, inverted image on a screen.
- It’s a great DIY tool to observe the basic principle of image formation.
🔭 Making Useful Optical Devices
Students learn how to build two optical devices:
- Periscope: Uses two mirrors to allow users to see over or around obstacles. Useful in submarines and bunkers.
- Kaleidoscope: A fun device using multiple reflections to create beautiful patterns. Artists and designers often use this for inspiration.
📌 Quick Recap of Key Concepts
- Light travels in straight lines.
- Shadows form when light is blocked.
- Reflection changes the direction of light.
- Plane mirrors produce virtual, erect, same-sized but laterally inverted images.
- Pinhole cameras create real, inverted images.
- Mirrors help build amazing tools like periscopes and kaleidoscopes.
