Keshav visits his friend Jatin's village in the Western Ghats and is amazed by the forests, streams, and especially the glowing dance of fireflies at night.
He learns from Jatin's grandparents that fireflies use light to communicate, but their numbers are falling due to light pollution and deforestation.
On the way back to the city, Keshav watches the moonlit hills and wonders - does the Moon produce its own light?
Or is it just reflected sunlight, like he read in his science book? As he thinks, he notices something interesting: light always travels in a straight line.
These thoughts lead him to explore sources of light, how light behaves when it meets different materials and how images and shadows are formed. Let's learn more.
Light enables us to see objects and is produced by various sources, both natural and artificial.
These include the Sun, stars, fire, lightning, and certain animals (like fireflies) that emit their own light. 
Humans have developed several artificial sources over time, beginning with fire created using fuels like oil and wax.
With technological advancement, electric lights such as bulbs, tube lights, and LED lamps have become common.
Some objects produce their own light, while others rely on the reflection of light. On this basis, objects can be divided into two types: luminous and non-luminous.
Science and Society
LED lamps are energy-efficient, brighter, and longer-lasting than traditional bulbs. They help reduce electricity bills and are environmentally friendly. Recognizing these benefits, the Indian government actively promotes their use. However, used LED lamps must be properly recycled and not discarded in regular waste.
MULTIPLE CHOICE QUESTIONTry yourself: What do fireflies use light for?
Light travels in a straight line under normal conditions, a property known as rectilinear propagation.
When light passes through aligned holes in a straight line, it creates a bright spot on a screen.
If the holes are misaligned, no spot appears, indicating that light does not bend around obstacles.
Similarly, a candle flame is visible through a straight pipe but not a bent one, confirming that light follows a straight path.
Viewing candle flame through (a) a straight pipe (b) a bent pipe
Dive Deeper
Light generally travels in a straight line. This can be seen clearly when a laser beam passes through a medium like water. However, under special conditions, light can also bend - a fascinating concept you'll explore in higher grades.
Caution: Lasers should always be used under teacher supervision. Only low-power laser pointers are safe for basic use. Never point a laser at anyone's eyes - it can cause serious injury.
When light encounters different materials, its behavior depends on the material's properties.
A shadow is a dark region formed when an object blocks light from reaching a surface.
Shadows require three components:
From the above observations, we can conclude:
Fascinating Facts
Shadow play, or shadow puppetry, is an ancient art where flat cut-out puppets are placed between a light source and a screen to create lifelike movements.
Different Indian regions have unique styles like Charma Bahuli Natya (Maharashtra), Keelu Bomme and Tholu Bommalata (Andhra Pradesh), Togalu Gombeyaata (Karnataka), Ravana Chhaya (Odisha), Tholpavakoothu (Kerala), and Bommalattam (Tamil Nadu).
These performances entertain and convey important community messages.
MULTIPLE CHOICE QUESTIONTry yourself: What type of materials allows light to pass through almost completely?
Reflection occurs when light bounces off a surface, changing its direction.
A plane mirror is a flat mirror that forms an image of an object placed in front of it. The image has several characteristic properties.
Image Characteristics
Distance Relationship: The image's distance from the mirror equals the object's distance from the mirror. Moving closer to the mirror makes the image appear closer, and moving farther makes it appear farther.
Fascinating Fact
The exact time when mirrors were invented is unknown. Early mirrors were made by polishing stone or metal. With the invention of glass mirrors, the traditional art of making metal mirrors faded but still survives in places like Kerala, where the unique Aranmula Kannadi metal mirror has been crafted for centuries.
A pinhole camera is a simple device that uses a tiny hole to form an image on a screen.
Light rays from an object pass through a small hole (pinhole) and form an inverted (upside-down) image on a screen, such as tracing paper. The image shows the object's colours but is reversed vertically.
A sliding pinhole cameraUse two cardboard boxes, one slightly smaller to slide inside the other. Make a small hole in one side of the larger box.
Cut a square on the opposite side of the smaller box and cover it with thin translucent paper (like tracing paper) to act as a screen.
Slide the smaller box inside the larger one so the tracing paper is inside.
Point the pinhole side towards a distant object in bright sunlight.
Look through the open side, cover your head and camera with a dark cloth to see the image clearly.
Adjust the smaller box forward or backwards until the image appears on the tracing paper.
MULTIPLE CHOICE QUESTIONTry yourself: What is a characteristic of the image formed by a plane mirror?
The image formed on the tracing paper is upside down (inverted).
The images show the colours of the objects on the other side.
Dive Deeper
A pinhole camera forms an upside-down image, while a mirror produces a laterally inverted image that is not upside down. These concepts will be explored further in higher grades.
The properties of light, such as its straight-line travel and reflection, are used to create practical devices.
Periscope
A Periscope
A kaleidoscope
| 1. What exactly is a shadow and how does it form when light hits an object? |  |
| 2. Why do shadows change size and shape throughout the day in real life? | |
| 3. What's the difference between a real image and a virtual image formed by mirrors? | |
| 4. How does a plane mirror reflect light differently from a curved mirror in CBSE Class 7 Science? | |
| 5. What does the law of reflection actually mean and why is it important for understanding mirrors? | |
