Chapter 11 — Light: Shadows and Reflections
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1) 20 Most Important Words (With Simple Hindi Meanings)
| # | Word | Meaning in Hindi (सरल) |
|---|---|---|
| 1 | Light | प्रकाश — जो हमें चीज़ें दिखाता है। |
| 2 | Luminous object | दीप्त वस्तु — जो अपना प्रकाश देती है (जैसे सूर्य, तारा)। |
| 3 | Non-luminous object | अदीप्त वस्तु — जो स्वयं नहीं चमकती, दूसरे के प्रकाश से दिखती है (जैसे चाँद)। |
| 4 | Natural source | प्राकृतिक प्रकाश स्त्रोत — सूर्य, तारे, बिजली चमकना आदि। |
| 5 | Artificial source | कृत्रिम प्रकाश स्त्रोत — बल्ब, ट्यूबलाइट, LED, मोमबत्ती। |
| 6 | Straight-line propagation | प्रकाश का सीधा चलना — प्रकाश सीधी रेखा में चलता है। |
| 7 | Transparent | पारदर्शी — जिससे प्रकाश लगभग पूरा निकल जाता है (काँच)। |
| 8 | Translucent | अर्धपारदर्शी — जिससे प्रकाश कुछ-कुछ निकलता है (ट्रेसिंग पेपर)। |
| 9 | Opaque | अपारदर्शी — जिससे प्रकाश नहीं निकलता (गत्ता, लकड़ी)। |
| 10 | Shadow | छाया — जहाँ प्रकाश नहीं पहुँचता, वहाँ बना गहरा भाग। |
| 11 | Screen | पर्दा/स्क्रीन — जिस सतह पर छाया/प्रकाश दिखे। |
| 12 | Reflection | परावर्तन — दर्पण/चमकीली सतह से प्रकाश की दिशा बदलना। |
| 13 | Plane mirror | समतल दर्पण — सपाट शीशा। |
| 14 | Image | प्रतिबिंब — दर्पण/उपकरण में दिखाई देने वाली आकृति। |
| 15 | Erect | सीधा — उल्टा नहीं; ऊपर-नीचे जैसा है वैसा। |
| 16 | Lateral inversion | पार्श्व उलटाव — दर्पण में दायाँ-बायाँ बदल जाना। |
| 17 | Virtual image | आभासी प्रतिबिंब — जिसे स्क्रीन पर पकड़ नहीं सकते (समतल दर्पण में)। |
| 18 | Pinhole camera | सूई-छिद्र कैमरा — छोटे छेद से उल्टा चित्र बनाता है। |
| 19 | Periscope | परास्कोप — दो दर्पणों से छिपी चीज़ें देखने का साधन। |
| 20 | Kaleidoscope | कैलीडोस्कोप — तीन दर्पणों से सुंदर पैटर्न दिखाने वाला यंत्र। |
2) Detailed Notes — Complete Coverage of the Chapter
11.1 Sources of Light
- Luminous — emit their own light: Sun, stars, lightning, fire, fireflies.
- Non-luminous — seen by reflected light: Moon reflects sunlight.
- Artificial — candles, oil lamps, bulbs, tube lights, LED (use less power, brighter, last longer; dispose/recycle properly).
11.2 Light Travels in a Straight Line
- Matchbox-holes activity: light spot appears only when holes are in one straight line → light moves straight.
- Pipe activity: candle flame seen through a straight pipe, not a bent one → straight-line path.
- In higher classes you’ll learn special cases where light seems to bend (e.g., refraction, scattering).
11.3 Transparent, Translucent & Opaque
- Transparent: allow almost all light (glass, clear water) → object seen clearly.
- Translucent: allow some light (butter paper, tracing sheet) → object looks blur.
- Opaque: block light (wood, cardboard) → object behind not seen.
- Shining a beam through a beaker with a drop of milk makes the straight path visible.
11.4 Shadow Formation
- Shadow appears when an object blocks light on a screen (wall, floor, card).
- Needs three things: light source + object (preferably opaque) + screen.
- Shade & size:
- Opaque → dark shadow; Translucent → light (faint) shadow; some Transparent → very faint.
- Object closer to source → larger, blurrier shadow.
- Object closer to screen → smaller, sharper shadow.
- Colour of object doesn’t change the shadow’s colour.
- Multiple sources can give multiple shadows.
11.5 Reflection of Light
- Shiny surfaces (polished steel, mirror) change the direction of light → this is reflection.
- Redirect sunlight/torch beam with a plane mirror to create a bright spot on another wall.
- Light still travels in straight lines before and after reflection.
11.6 Images in a Plane Mirror
- Image properties: same size as object, erect (not upside down), virtual (cannot be captured on screen).
- Distance: Image is as far behind the mirror as the object is in front.
- Lateral inversion: left and right appear swapped (AMBULANCE is written reversed on ambulances).
11.7 Pinhole Camera
- A tiny hole lets straight light rays form an image on a screen.
- Image is real & inverted (upside down) and shows colours but appears dim.
- Sliding the inner box (tracing paper screen) forward/back helps get a sharp image.
11.8 Useful Devices from Reflection
- Periscope: Two plane mirrors at 45° in a Z-path let you see over/around obstacles (submarines, bunkers).
- Kaleidoscope: Three mirrors form multiple reflections → beautiful, changing symmetric patterns (used by designers/artists).
Safety First ⚠️
- Use candles and matches only under adult supervision.
- Avoid shining bright torches/laser pointers into anyone’s eyes.
- Use low-power pointers for beam activities and never look into the beam.
Quick Recap (In a Nutshell)
- Objects with their own light are luminous; others are non-luminous.
- Light generally travels in straight lines.
- Transparent lets most light pass; translucent some; opaque none.
- Shadow needs a light source, object, and screen and changes with distances.
- Reflection is change of light’s direction by a mirror.
- Plane mirror image: same size, erect, virtual, laterally inverted; image distance = object distance.
- Pinhole camera gives a real, inverted, dim image on a screen.
- Periscope & kaleidoscope use mirror reflection in creative ways.
Eco-note: Prefer LED lighting to save energy, and recycle bulbs/LEDs responsibly.
Chapter 11: Light, Shadows & Reflections — Compact Practice
| # | Question | Answer |
|---|---|---|
| 1 | Object that emits its own light? | Luminous |
| 2 | Object seen only by reflected light? | Non-luminous |
| 3 | Flat mirror is called a ______. | Plane mirror |
| 4 | Change in direction of light by a mirror? | Reflection |
| 5 | Left–right reversal in mirror? | Lateral inversion |
| 6 | Material allowing some light? | Translucent |
| 7 | Surface where shadow forms? | Screen |
| 8 | Device with a tiny hole making an image? | Pinhole camera |
| 9 | Light travels in a ______ path. | Straight |
| 10 | Two-mirror viewer to see over obstacles? | Periscope |
| # | Statement | Answer |
|---|---|---|
| 1 | The Moon is a ______ object. | non-luminous |
| 2 | Opaque objects form ______ shadows. | dark |
| 3 | A shadow forms when light is ______ by an object. | blocked |
| 4 | Plane-mirror image is ______ in size as the object. | same |
| 5 | Mirror image cannot be obtained on a ______. | screen |
| 6 | Pinhole camera image is ______. | inverted |
| 7 | Transparent materials pass ______ of the light. | most |
| 8 | A periscope uses mirrors at about ______°. | 45 |
| 9 | Changing object colour ______ change shadow colour. | does not |
| 10 | A kaleidoscope shows beautiful ______. | patterns |
| # | Statement | T/F | Why? |
|---|---|---|---|
| 1 | Stars are non-luminous. | False | They produce their own light. |
| 2 | Light is visible through a bent tube. | False | Light travels in straight lines. |
| 3 | Translucent objects cast lighter shadows. | True | Some light passes through. |
| 4 | Object colour decides shadow colour. | False | Shadow depends on light, not object colour. |
| 5 | Plane-mirror image is upside down. | False | It is erect; only left–right flips. |
| 6 | Image distance equals object distance in a plane mirror. | True | Mirror symmetry rule. |
| 7 | Pinhole camera forms a real inverted image. | True | Rays actually meet on the screen. |
| 8 | Reflection is change in light direction by a mirror. | True | That’s the definition. |
| 9 | Two light sources can make two shadows. | True | Each source casts its own shadow. |
| 10 | Opaque objects pass a little light. | False | They pass none. |
| # | Question | Key Answer |
|---|---|---|
| 1 | What is a luminous object? One example. | Emits its own light; e.g., Sun, flame, LED. |
| 2 | Why can’t a plane-mirror image be caught on a screen? | It’s virtual—rays only appear to meet. |
| 3 | Two factors affecting shadow size/sharpness? | Distances (source–object–screen) and source size. |
| 4 | Reason for “AMBULANCE” written reversed? | Lateral inversion lets drivers read it correctly in mirrors. |
| 5 | Why is a pinhole image inverted? | Top/bottom rays cross at the tiny hole. |
| 6 | Transparent vs translucent (one example each). | Transparent: clear glass. Translucent: butter paper. |
| 7 | Use of a periscope? | See over/around obstacles (submarines, bunkers). |
| 8 | Define lateral inversion. | Left and right appear interchanged in a mirror. |
| 9 | Why can’t we see a candle through a bent tube? | Light doesn’t turn corners—straight-line travel. |
| 10 | Principle of a kaleidoscope? | Multiple reflections between three mirrors make patterns. |
| # | Question | Answer |
|---|---|---|
| 1 | Show light travels in a straight line. | Align three card holes and a torch to get a spot on a screen. If any card moves off-line, the spot disappears—confirming straight-line travel. |
| 2 | Essential conditions for shadow. | A light source, an object (preferably opaque), and a screen. The object must block light to create a dark region. |
| 3 | Four properties of plane-mirror images. | Same size, erect, laterally inverted, and virtual (cannot be caught on a screen). Also at equal distance behind the mirror. |
| 4 | Shadow vs mirror image. | Shadow is a dark outline with no colour/detail; a mirror image shows detail/colour but is virtual and laterally inverted. |
| 5 | Make a pinhole camera; why is image dim? | Two sliding boxes, tiny hole on one end, tracing-paper screen on the other. Few rays pass the small hole → dim image. |
| 6 | Effect of distances on shadows. | Near source → large/blurrier; near screen → smaller/sharper. Bigger sources increase penumbra (blur). |
| 7 | Two light sources & shadows. | Each source casts its own shadow; they overlap to form multiple/partial shadows in different directions. |
| 8 | Safety for light/laser tasks. | Avoid eyes; use low-power lasers; supervise flames; prevent reflective glare and keep flammables away. |
| 9 | Daily applications of reflection. | Rear/side mirrors, periscopes, solar cookers, cosmetics mirrors, and optical instruments. |
| 10 | Periscope vs kaleidoscope (principle & use). | Periscope: two mirrors at ~45° for viewing hidden scenes (utility). Kaleidoscope: three mirrors create symmetric patterns (design/art). |