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CBSE Notes Class 7 Science Chapter 11 Light: Shadows and Reflection
Light is essential for us to see objects around us. This chapter introduces students to the basic properties of light and explains how shadows and reflections are formed.
The chapter also explains reflection of light, which occurs when light bounces back from a surface. Mirrors are common examples of reflective surfaces. Students learn about different types of mirrors and how images are formed.
The concept of transparent, translucent, and opaque materials is also discussed. Transparent materials allow light to pass through completely, while opaque materials do not.
This chapter helps students understand everyday phenomena related to light and builds a foundation for more advanced topics in optics.
1.0Download CBSE Class 7 Science Chapter 11 Notes: Free PDF
Read the CBSE Class 7 Science Chapter 11 – Light: Shadows and Reflection Notes PDF to find out more about light, how shadows form, and how reflection works. These notes break down important ideas into easy-to-understand examples. Good for quick review and doing well on tests.
2.0Light : Shadows and Reflections Class 7 Science Chapter 4 – Revision Notes
Light is a form of energy that travels in straight lines and helps us see things. It forms shadows when blocked and bounces off surfaces by fixed laws, giving images in mirrors, pinhole cameras, kaleidoscopes and periscopes.
Key Concepts:
- Light and Sight: We see an object only when light from it enters our eyes.
- Luminous Objects: Make their own light, like the Sun, stars and a candle.
- Non-luminous Objects: Do not make their own light. We see them by reflected light, like the Moon and a book.
- Rectilinear Propagation: Light travels in straight lines.
- Speed of Light: About 3 × 10⁸ m/s in a vacuum. It is slightly less in water or glass.
- Materials: Transparent, translucent or opaque, based on how much light passes.
- Shadow: A dark area formed when an object blocks light.
- Reflection: Light bouncing back from a surface.
- Images: Real or virtual. A plane mirror gives a virtual, erect, laterally inverted image.
Sources of Light:
The Sun is the main natural source. Stars, lightning, natural fires and some animals also give their own light. Fire was the first artificial light. Today electric lights meet most needs.
LED Lamps:
LED lamps use little electricity, shine brighter and last longer than old bulbs. They save money and are good for the environment. Dispose of old LED lamps properly.
Properties of Light:
Light travels as waves and spreads in all directions. It needs no medium to travel. Sunlight reaches Earth in 8 minutes 20 seconds.
Transparent, Translucent and Opaque Materials:
- Transparent: Almost all light passes, so objects look clear. Examples: clear glass, clean water.
- Translucent: Some light passes and scatters, so objects look blurred. Examples: frosted glass, butter paper.
- Opaque: No light passes. Examples: wood, metal, bricks.
Shadows:
A shadow forms when an opaque or translucent object blocks light. It has the same shape as the object. A source, an object and a screen are needed.
- Characteristics: Always dark, whatever the colour. Forms opposite the light source. Shows only the outline.
- Object closer to the screen: Shadow becomes smaller and sharper.
- Object closer to the torch: Shadow becomes larger and blurred.
- Object tilted: Shadow shape changes.
- Sun at noon: Shortest shadow, just below the object.
- Morning or evening: Longer shadow. The lower the Sun, the longer the shadow.
- Very low or very near source: Very long, larger and distorted shadow.
- Shadow puppets: Sharp when puppets are close to the screen, blurred when far.
Reflection of Light:
Reflection is light being sent back when it strikes a surface.
- Incident ray: The ray that falls on the mirror.
- Reflected ray: The ray sent back.
- Normal: A line perpendicular to the surface at the point of incidence.
- First law: The incident ray, reflected ray and normal lie in the same plane.
- Second law: Angle of incidence equals angle of reflection (∠i = ∠r).
- Normal incidence: A ray along the normal retraces its path.
- Example: If ∠i = 60°, then ∠r = 60°.
- Lake: A calm lake gives a clear reflection. Wavy water gives a blurred one.
Real and Virtual Images:
- Real image: Rays actually meet. It can be obtained on a screen.
- Virtual image: Rays only appear to meet. It cannot be obtained on a screen.
Plane Mirror:
It has a flat, polished surface. Its image is virtual, erect, same size as the object, as far behind the mirror as the object is in front, and laterally inverted. AMBULANCE is printed reversed so it reads correctly in a rear view mirror. The Aranmula Kannadi of Kerala is a handmade metal-alloy mirror with no glass.
Pinhole Camera:
It works on straight-line travel of light. It has a tiny hole on one side and a translucent screen on the other. Rays cross at the hole, so the image is real and inverted. A closer object or a longer camera gives a larger image. It needs no lens or mirror. A dark room with a small hole in the window is a camera obscura. One natural example is the Virupaksha temple, Hampi.
Multiple Reflection:
Reflected light can be reflected again, as with a hairdresser's two mirrors.
- Kaleidoscope: Three mirrors at 60° make colourful symmetrical patterns from coloured glass bits.
- Periscope: Two parallel mirrors at 45° turn light twice, so we can see over or around obstacles.
- Uses of periscopes: Submarines, tanks, bunkers and simple models.
3.0Chapter 11 Terminologies to Know – Light : Shadows and Reflections:
- Luminous object: Makes its own light.
- Non-luminous object: Does not make its own light.
- Rectilinear propagation: Travel of light in straight lines.
- Vacuum: A space with no air or almost none.
- Transparent: Lets almost all light pass.
- Translucent: Lets some light pass.
- Opaque: Lets no light pass.
- Shadow: A dark area formed when light is blocked.
- Blurred: Not clear.
- Distorted: Changed from normal shape.
- Magnified: Looking larger than actual size.
- Diminished: Reduced in size.
- Reflection: Bouncing back of light.
- Incident ray: The ray that falls on a surface.
- Reflected ray: The ray sent back.
- Normal: A line perpendicular to the surface at the point of incidence.
- Plane mirror: A mirror with a flat surface.
- Real image: An image that can be obtained on a screen.
- Virtual image: An image that cannot be obtained on a screen.
- Lateral inversion: Left-right reversal of an image.
- Camera obscura: A dark place where an outside image forms through a tiny hole.
- Symmetrical: Both sides match exactly.
- Kaleidoscope: Makes patterns by multiple reflections.
- Periscope: Uses two mirrors to see around obstacles.
4.0Learning Guide for Class 7 Science – Light : Shadows and Reflections:
- Straight Line Test: Make pinholes in three cardboard sheets and line them up. Look through the last one at a candle. Observation: The candle is seen when the holes are in line, and not seen when the middle sheet is shifted.
- Bent Pipe Activity: Look at a candle through a straight pipe, then a bent pipe. Observation: The flame is seen only through the straight pipe, so light does not bend on its own.
- Laser in Milky Water: Add one drop of milk to water, darken the room and shine a laser through it. Observation: The beam shows as a bright straight line because milk particles scatter light.
- Law of Reflection Activity: Send a torch beam at 30°, 45° and 60° to the normal on a mirror. Observation: The angle of reflection equals the angle of incidence.
- Homemade Pinhole Camera: Slide a smaller box with a tracing-paper screen into a larger box with a pinhole. Use black cloth and bright sunshine. Observation: An inverted picture forms on the tracing paper.
- Image of the Sun: Hold a cardboard sheet with a pinhole in the Sun. Observation: A small round image of the Sun appears in the shadow.
- Homemade Kaleidoscope: Put three mirror strips in a tube with coloured beads at one end. Observation: Symmetrical patterns change with every small turn.
Everyday Examples:
- Sunlight through curtain holes makes straight beams.
- Torches and car headlights give focused beams.
- A calm lake gives a clear reflection.
- Ambulance lettering reads correctly in a rear view mirror.
Revision Tips:
- Shadow needs source, object and screen.
- Closer to the screen: smaller and sharper. Closer to the torch: larger and blurred.
- Pinhole image: real, inverted, no lens.
- Plane mirror image: virtual, erect, same size, laterally inverted.
- Practise drawing the reflection diagram with i = r.
Safety Rules:
- Never shine a laser at any person or animal.
- Recycle or dispose of old LED lamps properly.
5.0Explore Chapter-wise Class 7 science Notes
6.0Additional Study Materials for Class 7 Science
7.0Find the Right Study Resources for Class 7
8.0Key Features of Chapter 11 Light: Shadows and Reflection
- Nature of Light: It talks about how light is a type of energy that lets us see things.
- How Shadows Are Made: This explains how shadows are made when light hits something.
- Light Reflection: This is how light bounces off of things like mirrors.
- Plane Mirrors: Talks about how mirrors make images, how big they are, and where they are.
- Laws of Reflection: This book talks about the rules that govern how light reflects.
- Practical Uses: This includes uses in mirrors, periscopes, and other optical devices.