Achieve top scores with this master reference guide for DAV Class 6 Science Chapter 12: Light and Shadows from the official textbook The Living World. Here you will find 100% textbook exercise solutions (Sections A to E), structured 3-column scientific comparison tables (Image vs Shadow, Transparent vs Translucent vs Opaque), eclipse alignments, pinhole optics, and authentic DAV Board Exam Common Question Paper PYQs (2022–23 & 2023–24) with marking keys.
Part A: Fill in the Blanks
Carefully study the completed textbook statements with essential optics concepts highlighted:
- 1. An object that allows light to pass through it (almost) completely, is known as a transparent object. (Examples: Clean clear glass, pure water, clear air.)
- 2. A shadow is formed when an opaque object obstructs the path of light. (Cause: Light travels in straight lines and cannot bend around opaque obstacles.)
- 3. Light travels in a straight line. (Optical law: Known as the rectilinear propagation of light.)
- 4. A Lunar eclipse occurs on a full moon night. (Astronomical alignment: Sun → Earth → Moon in a straight line.)
- 5. When light is reflected from a plane mirror, it changes its direction. (Phenomenon: Regular reflection bouncing light rays at an angle equal to the incident angle.)
Part B: Write True or False for the Following Statements
Each statement is evaluated with a clear scientific explanation:
1. A shadow has the same colour as the object casting it.
Answer: FALSE.
Scientific Justification: A shadow is simply a dark region devoid of light formed where light rays are blocked. Regardless of whether an object is red, blue, or yellow, its shadow is always a uniform dark silhouette (black/grey).
2. The image formed by a pinhole camera is inverted.
Answer: TRUE.
Scientific Justification: Light rays from the top of an object travel in straight lines through the tiny pinhole and strike the bottom of the tracing screen, while rays from the bottom strike the top, forming an upside-down (inverted) real image.
3. The moon is a luminous body.
Answer: FALSE.
Scientific Justification: The moon does not emit light of its own. It is a non-luminous celestial body that appears bright only because its dusty surface reflects incident sunlight toward Earth.
4. A solar eclipse occurs on a new moon day.
Answer: TRUE.
Scientific Justification: A solar eclipse takes place when the Moon moves directly between the Sun and Earth (Sun → Moon → Earth), an astronomical configuration that occurs exclusively during the New Moon phase.
5. Opaque objects do not cast any shadow.
Answer: FALSE.
Scientific Justification: Opaque objects completely block light transmission, thereby creating the sharpest and darkest shadows when placed in front of a light source.
Part C: Tick the Correct Option
1. Objects, like the sun, which emit light of their own, are called-
(a) Non-luminous objects
(b) Opaque objects
(c) Luminous objects
(d) Transparent objects
Correct Option: (c) Luminous objects
Why this is correct: Luminous bodies possess an internal source of energy that produces and radiates light independently (e.g., Sun, stars, burning candle, glowing electric bulb).
2. An object, through which we can see partially, but not very clearly, is-
(a) Transparent
(b) Translucent
(c) Opaque
(d) Luminous
Correct Option: (b) Translucent
Why this is correct: Translucent materials transmit light only partially and scatter the rays in all directions, obscuring sharp vision (e.g., butter paper, frosted glass, tissue paper).
3. The ‘something’, which can change its shape and size, and may appear and disappear anywhere/anytime, is a-
(a) Mirror image
(b) Rainbow
(c) Shadow
(d) Lens
Correct Option: (c) Shadow
Why this is correct: The size, shape, and sharpness of a shadow dynamically change as the angle, distance, and position of the light source or object change relative to the ground.
4. When the sun (during early morning) is behind an object, the size of its shadow in comparison to that object is-
(a) Much smaller
(b) Same size
(c) Much larger (longer)
(d) Invisible
Correct Option: (c) Much larger (longer)
Why this is correct: In the early morning, the Sun is low on the horizon, casting slanted rays at an acute angle to the ground, which projects an elongated, much longer shadow.
5. The image, formed by a pinhole camera, is-
(a) Erect and virtual
(b) Inverted and real
(c) Erect and magnified
(d) Laterally inverted only
Correct Option: (b) Inverted and real
Why this is correct: Straight light rays intersecting through the small aperture project an inverted, real image on the translucent screen that can be caught on paper.
Part D: Answer the Following Questions in Brief
1. Classify the materials given below as opaque, transparent or translucent:
[air, smoke, fog, aluminium sheet, wooden board, cellotape, polythene sheet, lime juice, wax, rubber, frosted glass, cardboard]
Answer:
• Transparent Materials (allow light to pass completely): Air, clear cellotape, lime juice (filtered).
• Translucent Materials (allow light to pass partially): Smoke, fog, polythene sheet, wax, frosted glass.
• Opaque Materials (completely block light): Aluminium sheet, wooden board, rubber, cardboard.
2. State the type of path that light ordinarily follows when going from one point to another.
Answer:
Light ordinarily travels along a straight line path in a homogeneous optical medium. This fundamental property is scientifically termed the rectilinear propagation of light.
3. Do fishes cast shadows in water?
Answer:
Yes. Like all opaque bodies, a fish intercepts light rays and casts a shadow. If the fish swims close to the bottom bed of a shallow pond, a distinct shadow is visible on the sand. However, if the fish swims in deep ocean water far from any screen/bed, the shadow fades out due to surrounding scattered light before reaching the bottom.
4. On a sunny day, two identical bedsheets, of red and green colour, are hanging on a clothes line. What would be the colour of their shadows?
Answer:
Both bedsheets will cast dark (black/grey) shadows.
Reason: A shadow is an area of darkness caused by the physical obstruction of light rays. It is not an image and does not possess or reflect any color of the casting object.
5. State the relative positions of the sun, moon and the earth during a lunar eclipse.
Answer:
During a lunar eclipse, the Earth comes directly between the Sun and the Moon in a straight line:
Sun → Earth → Moon
The Earth blocks sunlight from reaching the Moon, casting Earth’s shadow across the lunar surface.
Part E: Answer the Following Questions (Long Answers)
1. Cover the face of a torch with a transparent coloured paper. Send its beam through an opaque object onto a screen. Does the colour of the shadow change? Explain.
Answer:
No, the colour of the shadow does not change; it remains dark/black.
Scientific Justification:
1. Covering the torch with coloured paper (e.g., red or blue cellophane) alters only the color of the light illuminating the surrounding screen.
2. The opaque object obstructs these light rays completely, preventing any light from reaching the shadow zone.
3. Since a shadow is purely the absence of light on the screen, it appears dark regardless of the color of the surrounding incident beam.
2. Show that the size of the shadow formed depends upon the relative distances between the source of light, the object, and the screen.
Answer:
The dimensions of a shadow are governed by geometric ray optics:
• Case 1 (Moving Object closer to Light Source): When an opaque object is moved closer to the light source (further from the screen), it intercepts a wider angle of diverging rays, casting a much larger (magnified) shadow on the screen.
• Case 2 (Moving Object closer to Screen): When the object is moved closer to the screen (away from the light source), it intercepts a narrower bundle of light rays, casting a smaller, sharper shadow approaching the true physical size of the object.
3. Raghav set up the following arrangement in the science laboratory. He put (i) a steel glass, (ii) a clean glass tumbler, (iii) a frosted glass tumbler in front of a torch beam. Compare the shadows formed on the screen.
Answer:
| Object | Optical Nature | Shadow Characteristics Formed on Screen |
|---|---|---|
| (i) Steel Glass | Opaque | Forms a sharp, very dark, distinct shadow because all light rays are completely blocked. |
| (ii) Clean Glass Tumbler | Transparent | Forms almost no visible shadow (only a faint outline of the glass edges) because light passes through unimpeded. |
| (iii) Frosted Glass Tumbler | Translucent | Forms a hazy, faint, greyish shadow because light is partially transmitted and partially scattered. |
4. Describe the formation of an image by a pinhole camera and state its key characteristics.
Answer:
A pinhole camera consists of a light-tight box with a tiny pinhole aperture on one face and a translucent tracing paper screen on the opposite face.
• Ray Mechanism: Light rays from the top of an illuminated object travel in straight lines through the tiny aperture to strike the bottom of the tracing paper screen. Similarly, rays from the bottom of the object pass through the aperture and strike the top of the screen.
• Image Characteristics:
1. The image is inverted (upside down).
2. The image is real (can be formed and seen directly on a physical screen).
3. The image retains the true colors of the object.
4. The size depends on the distance between the pinhole and the screen.
5. Give the meaning of the term ‘Lateral inversion’. Suggest how it may be used to send a ‘coded (secret)’ message.
Answer:
• Definition: Lateral inversion is the optical phenomenon in which the left side of an object appears as the right side in its plane mirror reflection, and vice versa.
• Encoding a Secret Message:
1. Write a confidential message on paper in reverse (mirror writing) from right to left with letters flipped laterally.
2. To an unassisted observer, the text appears scrambled and unreadable.
3. The intended recipient decodes the secret message simply by holding the paper in front of a plane mirror; the mirror laterally reinverts the flipped letters back into standard, legible text.
Value-Based Questions (VBQ) & HOTS
Value-Based Question (VBQ)
Scenario: During a solar eclipse, Sahil wanted to view the sun directly with naked eyes. His elder sister Riya stopped him immediately and handed him certified solar eclipse goggles (welder glass No. 14), explaining the biological danger to his eyes.
(a) Why should we never look directly at a solar eclipse with naked eyes?
Model Answer: Intense solar ultraviolet (UV) and infrared rays entering unprotected eyes can burn the photoreceptors of the retina (solar retinopathy), causing permanent, irreversible blindness.
(b) Identify two values shown by Riya:
Model Answer: Scientific awareness, protective care, and responsibility.
Higher Order Thinking Skills (HOTS)
Question: Why do we not see the shadow of an aeroplane flying high in the blue sky on the ground, even though it is an opaque body?
Model Answer: A flying aeroplane casts an umbra (dark shadow cone) and a surrounding penumbra. Because the aircraft flies at high altitude (thousands of feet above ground), its dark umbra cone ends in mid-air well before reaching the ground. The diverging penumbra is so faint and widely washed out by ambient daylight that no perceptible shadow appears on the ground.
🎯 DAV Board Exam Corner: Authentic PYQs (2022–23 & 2023–24)
Below are authentic questions directly retrieved from official DAV Public Schools Half-Yearly and Annual Board Papers for Chapter 12:
Q1. [DAV Half-Yearly Board Exam 2023–24 • 1 Mark VSA]
State three essential requirements for the formation of a shadow.
Model Answer: (1) A source of light; (2) An opaque object to block the light; (3) A screen or surface on which the shadow is cast.
Q2. [DAV Annual Board Exam 2022–23 • 2 Marks SA-I]
Distinguish between an Image and a Shadow.
Model Answer:
• Image: Formed by reflection or refraction of light; reveals the true colors, facial features, and details of the object; can be laterally inverted.
• Shadow: Formed by the obstruction of light rays by an opaque object; shows only a black outline (silhouette) without colors or internal details.
Q3. [DAV Annual Board Exam 2023–24 • 3 Marks SA-II]
State the positions of celestial bodies during a Solar Eclipse and mention the lunar phase when it occurs.
Model Answer:
• Alignment: The Moon moves directly between the Sun and the Earth in a straight line: Sun → Moon → Earth.
• Mechanism: The Moon casts its shadow onto portions of the Earth’s surface, blocking the Sun from view.
• Lunar Phase: Occurs strictly on a New Moon day (Amavasya).
Q4. [DAV Annual Board Exam 2022–23 • 5 Marks Long Answer]
Describe an experiment using a flexible rubber tube and a lighted candle to prove that light travels in a straight line.
Model Answer:
• Experimental Setup: Place a lighted candle firmly on a table. Take a straight, flexible hollow rubber tube about 30 cm long.
• Observation 1 (Straight Tube): Look at the candle flame through the rubber tube while keeping it completely straight. The bright flame is clearly visible.
• Observation 2 (Bent Tube): Now bend the rubber tube in the middle and look towards the candle flame. The flame is no longer visible.
• Scientific Conclusion: Light rays from the candle travel strictly in straight lines. When the tube is bent, straight light rays strike the inner walls of the tube and cannot bend around the curve, proving the rectilinear propagation of light.
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