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Light: Shadows and Reflections – Class 7 Science Chapter 11 Notes & NCERT PDF

Class 7ScienceChapter 11NCERT book: Curiosity - Science Class 7

Notes and a simple summary of Chapter 11 of the NCERT Class 7 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 11: Light: Shadows and Reflections

Introduction

In the Western Ghats of Maharashtra, Keshav spends his vacation at his friend Jatin's grandparents' village. He is amazed by hundreds of fireflies flashing at night — they use light to communicate, but their numbers are falling because of light pollution, reduced forest cover and excessive tourism. On the evening bus home, watching the moonlit landscape and vehicle headlights, Keshav wonders: does the Moon make its own light? And he notices that light seems to travel in a straight line!

Key Concepts

11.1 Sources of light

  • The Sun is the main source of natural light. Stars, lightning, natural fire and some animals (like fireflies) also emit light.
  • Humans first made fire with fuels like animal fat, oil, wax and gas; today electric lights meet most needs. LED lamps use much less power, are brighter and last longer — dispose of or recycle them properly.
    • Luminous objects emit their own light. Non-luminous objects do not. The Moon is non-luminous — it only reflects sunlight.

    11.2 Light travels in a straight line

  • Matchbox activity: a torch beam passes through holes in three matchboxes only when the holes are in a straight line.
  • Pipe activity: a candle flame is seen through a straight pipe but not a bent one.
  • A laser beam in water with a drop of milk also shows a straight path (under teacher supervision; never point lasers at eyes).

    • 11.3 Transparent, translucent, opaque

    Light passes almost completely through transparent materials (glass), partially through translucent ones (tracing paper), and not at all through opaque ones (cardboard, thick cloth).

    11.4 Shadows

    When an opaque object blocks light, the dark patch where light does not reach is its shadow. To see a shadow you need a source of light, an opaque object and a screen (wall, floor, ground).

  • Opaque objects make darker shadows; translucent objects make lighter ones; some transparent objects make faint shadows.
  • The shape, size and sharpness of a shadow depend on the object's position relative to the light and the screen.
  • Changing the colour of an opaque object does not change the colour of its shadow.
  • Shadow puppetry traditions: Charma Bahuli Natya (Maharashtra), Keelu Bomme and Tholu Bommalata (Andhra Pradesh), Togalu Gombeyaata (Karnataka), Ravana Chhaya (Odisha), Tholpavakoothu (Kerala), Bommalattam (Tamil Nadu).

    • 11.5 Reflection of light

    A shiny plate or plane mirror (a flat mirror) can redirect sunlight onto a wall. With a comb slit and torch, a thin beam changes direction on hitting a mirror.

    Reflection of light is the change in direction of light by a mirror (or shiny surface).

    11.6 Images in a plane mirror

    The image formed by a plane mirror is:

  • the same size as the object,
  • erect (upright),
  • cannot be obtained on a screen,
  • as far behind the mirror as the object is in front (stand closer — the image comes closer),
  • laterally inverted — left appears right and right appears left. That is why 'AMBULANCE' is written in mirror writing on ambulances, so drivers read it correctly in rear-view mirrors.

    • Kerala's Aranmula Kannadi is a traditional metal-surface mirror still made today.

    11.7 Pinhole camera

    A pinhole camera lets light from an object pass through a tiny hole to form an image on a screen.

    A candle flame seen through a pinhole appears upside down (inverted). A sliding box camera with tracing paper as the screen shows distant objects in their colours, but inverted. Contrast: a mirror image is laterally inverted but not upside down.

    11.8 Useful items

  • Periscope: two plane mirrors in a Z-shaped box let you see objects not directly visible — used in submarines, tanks and bunkers.
  • Kaleidoscope: three mirror strips joined in a triangle inside a tube with coloured bangle pieces; multiple reflections form ever-changing patterns that designers use for ideas.

    • Activities in the Chapter

  • 11.1 Three matchboxes in a line — bright spot only when holes are aligned → light travels straight.
  • 11.2 Candle through straight vs bent pipe → straight-line travel.
  • 11.3 Predict-then-observe light through cardboard, paper, glass, tracing paper, thick cloth → classify materials.
  • 11.4 Change screen, object, torch, distances, tilt and colour → learn what shadows need and how they change.
  • 11.5–11.6 Mirror redirects sunlight; comb-slit beam shows reflection.
  • 11.7–11.8 Pen and self in a mirror → image properties and lateral inversion.
  • 11.9–11.10 Candle pinhole image and sliding pinhole camera → inverted image.

    • Key Terms

  • Luminous object (दीप्त वस्तु) — emits its own light
  • Non-luminous object (अदीप्त वस्तु) — does not emit light
  • Transparent (पारदर्शी), Translucent (पारभासी), Opaque (अपारदर्शी)
  • Shadow (छाया) — dark patch where light is blocked
  • Reflection (परावर्तन) — change of direction of light by a mirror
  • Plane mirror (समतल दर्पण) — a flat mirror
  • Image (प्रतिबिंब) — what appears in the mirror or on the screen
  • Erect image (सीधा प्रतिबिंब) — upright image
  • Inverted image (उल्टा प्रतिबिंब) — upside-down image
  • Lateral inversion (पार्श्व परिवर्तन) — left-right reversal
  • Pinhole camera (सूचिछिद्र कैमरा)
  • Periscope (परिदर्शी), Kaleidoscope (बहुमूर्तिदर्शी)
  • Light pollution (प्रकाश प्रदूषण)

    • Real-life Connections

  • Sunlight takes about 8 minutes 20 seconds to reach the Earth.
  • Shadows are shortest around midday when the Sun is high.
  • Reduce light pollution to protect fireflies and night life.

    • Common Misconceptions

  • "The Moon shines by its own light." — It reflects sunlight.
  • "A blue object makes a blue shadow." — Shadow colour does not change with the object's colour.
  • "A mirror image is upside down." — It is erect but laterally inverted; the pinhole camera gives an upside-down image.
  • "Mirror images can be caught on a screen." — Plane-mirror images cannot.
  • "Transparent objects never form shadows." — Some can form faint shadows.

    • Keep the Curiosity Alive (exercise hints)

  • Luminous from the list: Sun and Pole Star (stars); Mars, Moon, Venus and a mirror are non-luminous.
  • A bird flying high makes no visible shadow on the ground, but one near the ground does — the distance from the ground affects the shadow.
  • Letters like T and O look the same in a mirror because they are left-right symmetric; lateral inversion still happens.
  • Periscope: fix two mirrors parallel to each other at 45° at the two bends of a Z-shaped tube.

    • 💡 Key Learning Points

    • ✓Luminous objects (Sun, stars, fireflies) emit light; non-luminous objects like the Moon only reflect it.
    • ✓Light travels in a straight line, shown by aligned matchbox holes and straight vs bent pipes.
    • ✓Materials are transparent, translucent or opaque; shadows need a light source, an opaque object and a screen, and their size/shape depend on positions.
    • ✓A plane mirror reflects light and forms an image that is same-size, erect, laterally inverted and cannot be caught on a screen.
    • ✓A pinhole camera forms an inverted image; periscopes and kaleidoscopes use plane-mirror reflections.

    👨‍🏫 Teaching Tips

    • →Open with Keshav's firefly story and ask: does the Moon make its own light? Sort a list into luminous and non-luminous.
    • →Do the matchbox and bent-pipe activities in small groups so every student sees light's straight path.
    • →Use a predict–observe table for different materials before shining the torch through them.
    • →Let students play with shadow shapes and systematically change object–torch–screen distances; link to Indian shadow puppetry.
    • →Have students raise their left hand in front of a mirror and read mirror-written 'AMBULANCE' to feel lateral inversion.
    • →Build sliding pinhole cameras from two boxes and view a sunlit tree — stress that the image is upside down.
    • →Make simple periscopes and kaleidoscopes as a take-home project.

    📋 Assessment Questions

    1. Can the student classify objects as luminous or non-luminous and materials as transparent, translucent or opaque?
    2. Can the student explain an activity that shows light travels in a straight line?
    3. Can the student list what is needed to form a shadow and predict how its size changes?
    4. Can the student state four properties of an image in a plane mirror, including lateral inversion?
    5. Can the student compare a pinhole-camera image with a plane-mirror image?

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    Keep learning

    All chapters in Curiosity - Science Class 7

    1. 1. The Ever-Evolving World of Science
    2. 2. Exploring Substances: Acidic, Basic, and Neutral
    3. 3. Electricity: Circuits and their Components
    4. 4. The World of Metals and Non-metals
    5. 5. Changes Around Us: Physical and Chemical
    6. 6. Adolescence: A Stage of Growth and Change
    7. 7. Heat Transfer in Nature
    8. 8. Measurement of Time and Motion
    9. 9. Life Processes in Animals
    10. 10. Life Processes in Plants
    11. 11. Light: Shadows and Reflections
    12. 12. Earth, Moon, and the Sun