Light: Shadows and Reflections

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True

False (the Moon is non-luminous; it reflects the light of the Sun)

True

False (you cannot see it through a bent pipe; light travels in a straight line)

True

False (changing the colour of the object does not change the colour of the shadow)

True

False (it is of the same size as the object)

True

False (it cannot be obtained on a screen)

True

False (a periscope uses two plane mirrors in a Z-shaped box)

False (it shows a different pattern every time it is turned)

True

True

(i)–(c), (ii)–(a), (iii)–(d), (iv)–(b), (v)–(e)

(i)–(b), (ii)–(c), (iii)–(a), (iv)–(b), (v)–(a)

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(a)

(d) (Both are true; R explains why translucent/transparent form lighter shadows but does not itself state that opaque blocks light completely to form darker shadows)

(b) (Changing the colour of the object does not change the colour of the shadow; R is true)

(a) (Both are true; R gives other properties of the image, not the reason for the size being the same)

(d) (Both are true, but lateral inversion is not the reason the image cannot be obtained on a screen)

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Hint: Luminous objects emit their own light (e.g., the Sun, a star); non-luminous objects do not emit their own light (e.g., the Moon, which reflects sunlight).

Hint: The Moon does not emit its own light; it only reflects the light of the Sun that falls on it.

Hint: (i) In the matchbox activity, a light spot is obtained on the screen only when the three holes are in a straight line; (ii) a candle flame can be seen through a straight pipe but not through a bent pipe.

Hint: Glass — transparent; cardboard — opaque; tracing paper — translucent.

Hint: A shadow is the dark patch formed where light does not reach; it is formed because light travels in a straight line and is blocked by an opaque object placed in its path.

Hint: A source of light, an opaque object, and a screen.

Hint: Light passes partially through translucent materials, so only part of the light is blocked, producing a lighter shadow; opaque objects block light completely, producing darker shadows.

Hint: No; changing the colour of opaque objects does not change the colour of the shadows — a shadow is just the dark region where light is blocked.

Hint: The change in direction of light when it falls on a shiny surface or a mirror is called reflection of light.

Hint: Any two: it is of the same size as the object; it is erect; it cannot be obtained on a screen; it is laterally inverted.

Hint: The perceived left-right reversal in an image formed by a plane mirror; e.g., when you raise your left arm, the image raises its right arm; 'AMBULANCE' is written laterally inverted so it reads correctly in a rear-view mirror.

Hint: So that it reads 'AMBULANCE' correctly when viewed in the rear-view mirror of the vehicle ahead of the ambulance.

Hint: A device in which light rays from an object pass through a tiny hole (pinhole) and form an image on a screen; it forms an inverted (upside down) image.

Hint: A periscope; used in submarines, tanks, or by soldiers to see objects not visible directly (outside their bunkers).

Hint: A device made by joining three rectangular plane mirror strips in a triangular manner inside a circular tube, with broken pieces of coloured bangles or beads; it shows beautiful, different patterns on turning.

Hint: A pinhole camera forms an inverted (upside down) image that can be obtained on a screen; a plane mirror forms an erect, laterally inverted image that cannot be obtained on a screen.

Hint: They must be appropriately disposed of or recycled to avoid environmental harm, since they are modern devices whose materials need proper handling.

Hint: The image appears to be at the same distance behind the mirror as you are in front of it; when you move closer the image appears closer, and when you move away it appears farther.

Hint: If the Sun suddenly stopped emitting light, we would not know for another 8 minutes 20 seconds, because its light takes that long to travel to Earth.

Hint: Aranmula Kannadi; it is a unique metal-surface mirror made for centuries, preserving the old art of making metal mirrors even after glass mirrors became common.

Introduction: The matchbox activity demonstrates how light travels using three matchboxes with holes aligned in a line.
Key Points:
1. Holes aligned — Three matchboxes with holes at the same height are arranged in a straight line with a torch and screen.
2. Light spot seen — When holes are aligned, a bright spot of light appears on the screen behind the matchboxes.
3. Misaligned holes — When one matchbox is moved, the light spot disappears because the path is blocked.
Conclusion: The activity shows that light travels in a straight line.

Introduction: The bent-pipe activity uses a flexible pipe to view a candle flame and show that light travels straight.
Key Points:
1. Straight pipe — Looking through a straight pipe, the candle flame is clearly visible to the eye.
2. Bent pipe — When the pipe is bent, the candle flame can no longer be seen through it.
3. Conclusion drawn — Since light cannot bend around the pipe, it shows that light travels only in a straight line.
Conclusion: Light cannot bend, so it travels in a straight line as shown by this activity.

Introduction: Materials are classified as transparent, translucent, or opaque depending on how much light passes through them.
Key Points:
1. Transparent materials — Light passes almost completely through them, e.g., glass.
2. Translucent materials — Light passes only partially through them, e.g., tracing paper.
3. Opaque materials — Light does not pass through them at all, e.g., cardboard.
Conclusion: The amount of light passing through a material decides whether it is transparent, translucent, or opaque.

Introduction: A shadow is a dark patch formed when an opaque object blocks the path of light.
Key Points:
1. Shadow formation — When light is blocked by an opaque object, a dark region called a shadow forms behind it.
2. Requirements — A source of light, an opaque object, and a screen are needed to observe a shadow.
3. Opaque objects darker — Opaque objects block all light, so they form darker shadows than translucent or transparent objects.
Conclusion: Shadows form when light is blocked, and opaque objects create the darkest shadows.

Introduction: An activity using opaque objects of different shapes and sizes studies how shadows change with position.
Key Points:
1. Activity set-up — Opaque objects are placed between a fixed torch and a screen, and moved closer, farther, or tilted.
2. Conclusion one — The size and shape of the shadow depend on the position of the object relative to the light and screen.
3. Conclusion two — Changing the colour of the opaque object does not change the colour of the shadow.
Conclusion: A shadow's size and shape depend on the object's position, but its colour does not depend on the object's colour.

Introduction: Reflection of light can be shown by using a plane mirror or a shiny steel plate to redirect sunlight.
Key Points:
1. Mirror in sunlight — A plane mirror or shiny steel plate is held so that sunlight falls on its surface.
2. Light redirected — Tilting the mirror redirects a spot of light onto a wall where sunlight does not fall directly.
3. Reflection observed — The mirror changes the direction of light, which is called reflection of light.
Conclusion: A plane mirror changes the direction of light falling on it, showing reflection of light.

Introduction: A plane mirror forms an image of an object placed in front of it with certain definite properties.
Key Points:
1. Same size — The image formed is of the same size as the object placed in front of the mirror.
2. Erect — The image is upright, meaning the top of the object appears at the top of the image.
3. Cannot be obtained on a screen — The image is virtual and cannot be captured on a screen placed behind the mirror.
4. Laterally inverted — The left side of the object appears as the right side in the image, and vice versa.
Conclusion: A plane mirror forms an erect, same-size, laterally inverted, virtual image of the object.

Introduction: Lateral inversion is the left-right reversal seen in the image formed by a plane mirror.
Key Points:
1. Activity — Raise your left arm in front of a mirror; the image appears to raise its right arm.
2. Left-right reversal — The left side of the object appears on the right in the image, which is called lateral inversion.
3. Use for AMBULANCE — The word is written laterally inverted so it reads correctly in the rear-view mirror of vehicles ahead.
Conclusion: Lateral inversion makes the word 'AMBULANCE' readable to drivers looking through their rear-view mirrors.

Introduction: A pinhole camera is a simple device that forms an image of an object using a tiny hole.
Key Points:
1. Two sliding boxes — Two cardboard boxes are used, one sliding into the other with a small gap.
2. Pinhole and screen — A pinhole is made in the larger box; a translucent paper screen is fixed on the smaller box.
3. Inverted image — Light from the object passes through the pinhole and forms an upside-down (inverted) image on the screen.
Conclusion: A pinhole camera forms an inverted image of an object on a screen using light passing through a tiny hole.

Introduction: A periscope is a device that uses two plane mirrors to see objects that are not directly visible.
Key Points:
1. Construction — Two plane mirrors are placed in a Z-shaped box, each tilted so they face each other.
2. Working — Light from an object reflects off both mirrors in turn, allowing the viewer to see objects around obstacles.
3. Uses — Periscopes are used in submarines to see above water and in tanks by soldiers to see outside bunkers.
Conclusion: A periscope uses two mirrors to reflect light and lets users see objects hidden from direct view.

Introduction: A kaleidoscope is a tube-shaped instrument that produces colourful patterns using multiple reflections.
Key Points:
1. Mirror strips — Three rectangular mirror strips are joined in a triangular shape and fixed inside a circular tube.
2. Coloured pieces — Broken pieces of coloured bangles or beads are placed at one end over a transparent sheet.
3. Multiple reflections — Reflections of reflections between the three mirrors create a different beautiful pattern each time it is turned.
Conclusion: The kaleidoscope shows beautiful, changing patterns because multiple reflections of coloured pieces occur between the mirrors.

Introduction: A plane mirror and a pinhole camera form images that differ in orientation and nature.
Key Points:
1. Plane mirror image — The image is erect (upright) and laterally inverted, but not upside down.
2. Pinhole camera image — The image is upside down (inverted) but not laterally inverted like a mirror image.
3. Reason — The mirror reflects light back, while the pinhole lets light rays cross over, turning the image upside down.
Conclusion: A plane mirror forms an erect, laterally inverted image, whereas a pinhole camera forms an inverted image.

Introduction: The Sun is very bright and powerful, so looking at it directly can seriously harm our eyes.
Key Points:
1. Danger to eyes — The Sun's intense light can damage the eyes and even cause blindness if viewed directly.
2. Use protection — One should never view the Sun directly, even through sunglasses, binoculars, or telescopes.
3. 8 minutes 20 seconds — Sunlight takes about 8 minutes 20 seconds to reach Earth, so we see the Sun as it was earlier.
Conclusion: We must never look at the Sun directly because its intense light damages the eyes.

Introduction: A mirror can be used to redirect sunlight onto a wall and demonstrate reflection of light.
Key Points:
1. Mirror in sunlight — A shiny steel plate or plane mirror is held so that sunlight falls on its surface.
2. Spot on wall — Tilting the mirror in different directions places a spot of light on a wall or surface.
3. What it shows — The mirror changes the direction of light, which is called reflection of light.
Conclusion: This activity shows that a mirror changes the direction of light, demonstrating reflection.

Introduction: The pipe activity shows that only a person aligned in a straight line with the flame can see it.
Key Points:
1. Straight pipe needed — The candle flame is visible only when the eye, pipe, and flame are all in a straight line.
2. Bent path fails — If the pipe is bent or misaligned, the flame cannot be seen because light cannot bend.
3. Principle — This shows the principle that light always travels in a straight line.
Conclusion: The activity demonstrates that light travels in a straight line, so only an aligned viewer can see the flame.

Hint: (a) Fireflies use light to communicate. (b) Due to light pollution, reduced forest cover, and excessive tourism. (c) The Moon is a non-luminous object because it does not emit its own light; it only reflects the light of the Sun that falls on it.

Hint: (a) A bright spot of light is obtained on the screen. (b) The light spot can no longer be obtained on the screen. (c) Light travels in a straight line; another activity — viewing a candle flame through a straight pipe but not through a bent pipe.

Hint: (a) Glass — transparent; cardboard — opaque; tracing paper — translucent. (b) A source of light, an opaque object, and a screen. (c) Opaque materials block light completely, so a darker shadow forms; translucent materials let light pass partially, so only part of the light is blocked and a lighter shadow forms.

Hint: (a) No, it cannot be obtained on a screen. (b) Lateral inversion. (c) It is of the same size as the object; it is laterally inverted (left appears right); the image appears to be at the same distance behind the mirror as the object is in front.

Hint: (a) An inverted (upside down) image on a screen. (b) Through a tiny hole (pinhole). (c) The pinhole camera image is inverted (upside down) and can be obtained on a screen; the plane mirror image is erect and laterally inverted and cannot be obtained on a screen.

Hint: (a) Two plane mirrors, placed in a Z-shaped box. (b) Submarines and tanks (or by soldiers to see outside their bunkers). (c) Light from the object reflects off the first mirror to the second mirror and then to the viewer's eye; the two reflections bend the path of light so that the viewer can see an object around an obstacle that is not directly visible.

Hint: (a) Three rectangular plane mirror strips. (b) Broken pieces of coloured bangles or beads. (c) Because there are three mirrors and multiple images are formed due to reflections of reflections, so many different patterns appear; designers and artists often use kaleidoscopes to get ideas for new patterns.

Hint: (a) A source of light (torch), an opaque object (ball), and a screen (wall). (b) When the ball is closer to the torch, the shadow is larger. (c) Two shadows would appear on the screen — each torch sends light in a straight line and is blocked by the ball from a different direction, so two separate shadows (or overlapping regions) are formed.

Hint: (a) They consume less power, are brighter, and last longer than traditional lamps. (b) Because they reduce electricity bills and are better for the environment. (c) They must be appropriately disposed of or recycled, not thrown in the garbage, so that their materials are handled safely and do not harm the environment.

Hint: (a) An inverted (upside down) image. (b) The name appears laterally inverted (left-right reversed); this is called lateral inversion. (c) A pinhole camera forms an inverted (upside down) image because light rays pass straight through the pinhole and cross over, and it can be obtained on a screen; a plane mirror forms an erect but laterally inverted image due to reflection, and it cannot be obtained on a screen.

Introduction: Light comes from natural and artificial sources, and objects are classified based on whether they emit their own light.
Key Points:
1. Natural sources — The Sun is the main natural source of light; stars, lightning, fire, and some animals like fireflies also emit light.
2. Luminous objects — Objects that emit their own light are called luminous objects, e.g., the Sun and stars.
3. Non-luminous objects — Objects that do not emit their own light are called non-luminous objects, e.g., the Moon and a book.
4. Early artificial light — In ancient times, humans created fire using animal fat, oil, wax, and gas as the earliest artificial lighting.
5. Modern lighting — With the invention of electricity, electric bulbs and energy-efficient LED lamps now meet most lighting needs.
Conclusion: Light sources range from natural luminous objects like the Sun to modern electric and LED lamps developed over time.

Introduction: Two simple activities — the matchbox activity and the bent-pipe activity — show that light travels in a straight line.
Key Points:
1. Matchbox activity — Three matchboxes with aligned holes let a light spot fall on a screen; misaligned holes block the spot.
2. Bent-pipe activity — A candle flame is visible through a straight pipe but not through a bent pipe.
3. Both show straight path — In both activities, light reaches the eye or screen only when the path is straight.
4. Laser in water — A laser beam passed through milky water also appears to follow a straight path.
5. Conclusion — Since light cannot bend around obstacles or corners, it must travel in a straight line.
Conclusion: Both activities prove that light travels in a straight line.

Introduction: A shadow is a dark patch formed when an opaque object blocks the path of light.
Key Points:
1. Shadow formation — When an opaque object is placed in the path of light, a dark region called a shadow forms behind it.
2. Requirements — A source of light, an opaque object, and a screen are needed to observe a shadow.
3. Effect of position — Moving the object closer to the light makes the shadow larger; closer to the screen makes it smaller.
4. Tilting changes shape — Tilting the object changes the shape and sharpness of the shadow on the screen.
5. Colour does not matter — Changing the colour of the opaque object does not change the colour of the shadow.
Conclusion: Shadows form when light is blocked, and their size and shape depend on the object's position, not its colour.

Introduction: Reflection of light is the change in the direction of light when it strikes a mirror or shiny surface.
Key Points:
1. Definition — The change in the direction of light by a mirror is called reflection of light.
2. Activity — A thin beam of light from a torch through a comb slit is directed onto a plane mirror; the beam reflects away.
3. Same size image — The image formed by a plane mirror is of the same size as the object.
4. Erect and virtual — The image is erect (upright) and cannot be obtained on a screen.
5. Laterally inverted — The left and right sides of the object appear reversed in the image.
Conclusion: Reflection by a plane mirror forms a same-size, erect, laterally inverted, virtual image of the object.

Introduction: Lateral inversion is the left-right reversal that occurs in the image formed by a plane mirror.
Key Points:
1. Arm activity — Stand before a mirror and raise your left arm; the image appears to raise its right arm.
2. Paper activity — Writing your name on paper and holding it before the mirror shows the letters reversed left to right.
3. Left-right reversal — The left side of the object appears on the right in the image, which is lateral inversion.
4. AMBULANCE written inverted — The word is painted laterally inverted on the front of ambulances.
5. Reason — This makes the word read correctly as 'AMBULANCE' in the rear-view mirror of vehicles ahead.
Conclusion: Lateral inversion causes left-right reversal, which is used so 'AMBULANCE' is readable in rear-view mirrors.

Introduction: A pinhole camera is a simple device that forms an image using light passing through a tiny hole.
Key Points:
1. Definition — It is a device in which light rays from an object pass through a pinhole to form an image on a screen.
2. Construction — Two sliding cardboard boxes are used; a pinhole is made in one and a translucent screen on the other.
3. Inverted image — The image formed is upside down (inverted) and real, as it can be obtained on a screen.
4. Plane mirror image — A plane mirror forms an erect and laterally inverted virtual image, not an upside-down one.
5. Difference — The pinhole camera image is inverted and real, while the plane mirror image is erect and virtual.
Conclusion: A pinhole camera forms an inverted real image, unlike the erect virtual image of a plane mirror.

Introduction: A periscope and a kaleidoscope are useful devices made using plane mirrors and the principle of reflection.
Key Points:
1. Periscope construction — Two plane mirrors are placed in a Z-shaped box, each tilted to face the other.
2. Periscope working and use — Light reflects off both mirrors, letting the viewer see hidden objects; used in submarines.
3. Kaleidoscope construction — Three mirror strips are joined in a triangle inside a tube with coloured beads at one end.
4. Kaleidoscope working — Multiple reflections of the coloured pieces create changing, beautiful patterns when turned.
5. Kaleidoscope use — Designers and artists use kaleidoscopes to get ideas for new patterns.
Conclusion: The periscope helps see hidden objects, while the kaleidoscope creates patterns through multiple reflections.

Introduction: Materials are classified by how much light passes through them, which also affects the shadows they form.
Key Points:
1. Transparent materials — Light passes almost completely through them, e.g., glass; they form faint or no shadows.
2. Translucent materials — Light passes partially through them, e.g., tracing paper; they form lighter shadows.
3. Opaque materials — Light does not pass through them, e.g., cardboard; they form darker shadows.
4. Activity — A torch is shone on a screen, and different materials are placed between to observe how much light passes.
5. Shadow dependence — The darkness of a shadow depends on how much light the material blocks.
Conclusion: The type of material decides how much light passes through and how dark the shadow is.

Introduction: Shadow puppetry is a traditional Indian art form in which flat cut-out figures create moving shadows on a screen.
Key Points:
1. Art form — Flat cut-out figures called shadow puppets are placed between a light source and a screen.
2. Life-like movement — Puppeteers move the puppets and the light to create life-like movements of the characters.
3. Regional styles — Styles include Togalu Gombeyaata (Karnataka) and Ravana Chhaya (Odisha).
4. More styles — Tholpavakoothu (Kerala) and Bommalattam (Tamil Nadu) are other regional forms.
5. Science behind it — Opaque puppets block light, forming shadows on the screen, since light travels straight.
Conclusion: Shadow puppetry uses the principle that opaque objects block light to form shadows, creating a cultural art form.

Introduction: The chapter teaches the basic properties of light and how we use them to understand shadows and reflections.
Key Points:
1. Sources of light — Luminous objects like the Sun emit their own light; non-luminous objects like the Moon do not.
2. Straight-line travel — Light travels in a straight line, as shown by the matchbox and bent-pipe activities.
3. Shadows — A shadow forms when an opaque object blocks light; it needs a light source, object, and screen.
4. Reflection and plane mirror — A mirror reflects light, forming an erect, same-size, laterally inverted, virtual image.
5. Devices — A pinhole camera forms an inverted image, a periscope shows hidden objects, and a kaleidoscope makes patterns.
Conclusion: The chapter explains how light's straight-line travel and reflection create shadows, images, and useful devices.