Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
NCERT Solutions for Class 6 Science Chapter 11 — Light, Shadows and Reflections
Key Concepts at a Glance
| Term | Definition |
|---|---|
| Light | A form of energy that enables us to see objects; travels in straight lines |
| Luminous objects | Objects that emit their own light — e.g., sun, torch, candle, stars, firefly |
| Non-luminous objects | Objects that do not emit their own light but reflect light — e.g., moon, book, wall, tree |
| Transparent objects | Objects through which light passes completely — e.g., glass, clear water, cellophane |
| Translucent objects | Objects through which light passes partially — e.g., frosted glass, butter paper, oily paper |
| Opaque objects | Objects that do not allow any light to pass through — e.g., wood, metal, cardboard, stone |
| Shadow | A dark region formed when an opaque object blocks the path of light |
| Rectilinear propagation of light | The property of light travelling in straight lines; explains shadow formation and pinhole camera |
| Pinhole camera | A simple camera that forms an inverted image using a small pinhole; works on rectilinear propagation |
| Reflection | The bouncing back of light from a surface; e.g., seeing your face in a mirror |
| Mirror | A smooth, shiny surface (usually glass coated with metal) that reflects light regularly |
| Eclipse | A shadow cast by one celestial body on another — solar eclipse (moon casts shadow on earth) and lunar eclipse (earth casts shadow on moon) |
Intext Questions (with Answers)
Intext Question 1 (Page 113)
Classify the objects or materials given below as opaque, transparent, or translucent:
Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a thin sheet of paper, a sheet of cardboard, a flame of a gas burner, a sheet of cellophane, a wire mesh, kerosene, a thick sheet of glass, wax, spectacles, a piece of carbon paper.
| Category | Objects |
|---|---|
| Transparent | Air, water, a sheet of plane glass, a sheet of cellophane, a thin sheet of glass (spectacles lens) |
| Translucent | A sheet of polythene, smoke, fog, a thin sheet of paper, kerosene, wax, butter paper |
| Opaque | A piece of rock, a sheet of aluminium, a mirror, a wooden board, a CD, an umbrella, a lighted fluorescent tube (glass is translucent but coated material makes it opaque), a piece of red hot iron, a sheet of cardboard, a flame of a gas burner, a wire mesh (densely woven), a thick sheet of glass, a piece of carbon paper |
Intext Question 2 (Page 114)
Can you think of creating a shape that would give a circular shadow if held in one way and a rectangular shadow if held in another way?
Yes! A cylinder (like a pencil or a pipe) can do this:
- When the cylinder is held vertically (with its circular base facing the light), it casts a circular shadow.
- When the cylinder is held horizontally (with its curved side facing the light), it casts a rectangular shadow.
This happens because the shape of the shadow depends on the orientation of the object relative to the light source. The shadow shows the cross-section of the object as seen from the direction of the light.
Intext Question 3 (Page 115)
In a completely dark room, if you hold up a mirror in front of your face, can you see your reflection in the mirror?
No, you cannot see your reflection in a mirror in a completely dark room. This is because:
1. A mirror can only reflect light — it does not produce its own light. 2. In a dark room, there is no light to fall on your face and bounce off towards the mirror. 3. Without light, there is nothing to reflect, so no image is formed in the mirror.
This proves that we need light to see objects, including our own reflection. The mirror itself is not a source of light.
Intext Question 4 (Page 116)
What are the conditions necessary for the formation of a shadow?
Three conditions are necessary for the formation of a shadow:
1. A source of light — There must be a light source (sun, torch, lamp). 2. An opaque object — There must be an opaque or partially opaque object in the path of light. 3. A screen or surface — There must be a surface on which the shadow is cast (a wall, the ground, or any surface).
If any one of these three is missing, a shadow will not form.
Intext Question 5 (Page 117)
What is the difference between a shadow and a reflection?
| Feature | Shadow | Reflection |
|---|---|---|
| Definition | Dark area formed when an opaque object blocks light | Image formed when light bounces off a smooth, shiny surface |
| Requires | Light source, opaque object, and screen | Light source and smooth, reflective surface (mirror) |
| Colour | Always dark/black | Shows colours of the original object |
| Detail | Does not show details of the object | Shows details — features, colours, and shape |
| Dependence | Depends on the shape and orientation of the object | Depends on the smoothness of the reflecting surface |
| Example | Your shadow on the ground in sunlight | Seeing your face in a mirror |
Intext Question 6 (Page 118)
How does a pinhole camera form an image?
A pinhole camera forms an image using the principle that light travels in straight lines:
1. Light from the top of the object passes through the pinhole and reaches the bottom of the screen. 2. Light from the bottom of the object passes through the pinhole and reaches the top of the screen. 3. Light from the left side reaches the right side of the screen. 4. Light from the right side reaches the left side of the screen.
As a result, the image formed is inverted (upside-down and left-right reversed).
The image is:
- Real — It can be obtained on a screen
- Inverted — Upside down
- Dimmer — Less bright than the object (only a small amount of light passes through the pinhole)
Intext Question 7 (Page 119)
State whether the following statements are True or False:
(a) The moon is a luminous object.
(b) Light travels in straight lines.
(c) A transparent object allows light to pass through it completely.
(d) A shadow can be formed even when there is no screen.
(e) The image formed in a pinhole camera is upright.
Intext Question 8 (Page 120)
Give one word for the following:
(a) Objects that emit their own light.
(b) Objects that do not allow light to pass through them.
(c) The bouncing back of light from a surface.
(d) A dark outline formed when an opaque object blocks light.
(e) Objects that allow some light to pass through but not clearly.
Intext Question 9 (Page 120)
Why is a burning candle both luminous and opaque?
A burning candle is:
- Luminous — The flame of the candle emits its own light, making it a luminous object.
- Opaque — The wax body of the candle does not allow light to pass through it.
Different parts of an object can have different properties. The flame is luminous (emits light), while the wax body is opaque (blocks light). This shows that an object can have more than one property simultaneously.
Intext Question 10 (Page 121)
Rearrange the boxes given below to make a sentence that helps us understand opaque objects.
| OPAQUE | OBJECTS | MAKE | SHADOWS | AND | ARE | NOT | TRANSPARENT |
|---|
This sentence captures the key idea: opaque objects block light completely, casting shadows, and they do not allow any light to pass through (unlike transparent objects).
Exercise Questions (with Answers)
Exercise Question 1
Name the type of objects through which we can see clearly.
We can see clearly through transparent objects. These objects allow light to pass through them completely, enabling us to see what is on the other side.
Examples: Clear glass, pure water, cellophane sheet, air.
In contrast, translucent objects allow only partial light (we see a blurred image), and opaque objects block all light (we cannot see through them at all).
Exercise Question 2
What is a shadow? How is it formed?
A shadow is a dark region formed on a screen or surface when an opaque or translucent object comes in the path of light.
How a shadow is formed:
1. Light travels in straight lines (rectilinear propagation). 2. When an opaque object is placed in the path of light, it blocks the light rays. 3. The area behind the object, where light cannot reach, appears dark — this is the shadow. 4. The shadow has the same outline as the object but may differ in size depending on the distance between the light source and the object.
Conditions for shadow formation:
- A source of light
- An opaque or translucent object
- A screen or surface
Exercise Question 3
State the differences between transparent, translucent, and opaque objects.
| Feature | Transparent | Translucent | Opaque |
|---|---|---|---|
| Light transmission | All light passes through | Some light passes through | No light passes through |
| Visibility | Can see through clearly | Can see partially (blurred) | Cannot see through at all |
| Shadow | No shadow or very faint shadow | Faint shadow | Dark, clear shadow |
| Examples | Clear glass, pure water, air | Frosted glass, butter paper, wax | Wood, metal, cardboard, stone |
Exercise Question 4
What is reflection of light? Give two examples.
Reflection of light is the process in which light bouncing off a smooth, shiny surface changes direction and comes back to the same side. When light falls on a polished or shiny surface, it is reflected, and we can see an image.
Examples: 1. Mirror — When you stand in front of a mirror, you see your reflection because light from your face bounces off the mirror. 2. Still water surface — When you look into a calm pool of water, you can see the reflection of trees, sky, and buildings.
Other examples: polished metal surface, shiny foil, new steel utensil.
Exercise Question 5
Explain why a shadow is always black (dark) in colour.
A shadow is always dark because it is the region where light does not reach. When an opaque object blocks the path of light, the area behind it receives no light. Since we see objects only when light reaches our eyes from them, the region with no light appears dark.
A shadow is not necessarily "black" — it is simply the absence of the light source that illuminates the rest of the area. If there are other light sources in the room, the shadow may appear less dark, but it will still be darker than the illuminated area.
Exercise Question 6
What is a pinhole camera? Draw a neat diagram and explain how it works.
A pinhole camera is a simple camera made from a box with a small pinhole on one side and a screen (tracing paper/translucent sheet) on the opposite side.
How it works: 1. Light from the object travels in straight lines. 2. Light rays from the top of the object pass through the pinhole and hit the bottom of the screen. 3. Light rays from the bottom of the object pass through the pinhole and hit the top of the screen. 4. Similarly, left-side rays hit the right side and right-side rays hit the left side. 5. An inverted (upside-down) image of the object is formed on the screen.
Properties of the pinhole camera image:
- Real (can be caught on a screen)
- Inverted (upside down)
- Smaller than the object (usually)
Exercise Question 7 (MCQ)
Which of the following is a luminous object?
(a) Moon ✗ (b) Book ✗ (c) Sun ✓ (d) Chair ✗
The Sun emits its own light and is therefore a luminous object. The moon reflects sunlight and does not emit its own light. A book and a chair are non-luminous objects.
Exercise Question 8 (MCQ)
Which of the following is a translucent object?
(a) Glass ✗ (b) Wood ✗ (c) Butter paper ✓ (d) Iron sheet ✗
Butter paper allows some light to pass through but not clearly, making it translucent. Glass is transparent (allows all light through clearly). Wood and iron sheet are opaque (allow no light through).
Exercise Question 9
Why do we see lightning before we hear thunder, even though both happen at the same time?
We see lightning before we hear thunder because light travels much faster than sound:
- Speed of light = approximately 3,00,000 km/s (3 × 10⁸ m/s)
- Speed of sound = approximately 340 m/s (in air)
Light reaches our eyes almost instantly, while sound takes much longer to travel the same distance. For example, if lightning strikes 3 km away:
- Light takes about 0.00001 seconds to reach us (almost instant)
- Sound takes about 8.8 seconds to reach us (3,000 m ÷ 340 m/s)
This is why we see the flash of lightning first and hear the thunder a few seconds later.
Exercise Question 10
Match the following:
| Column A | Column B |
|---|---|
| (a) Luminous object | (i) Allows some light to pass through |
| (b) Transparent object | (ii) Blocks all light |
| (c) Opaque object | (iii) Emits its own light |
| (d) Translucent object | (iv) Allows all light to pass through |
| Column A | Column B |
|---|---|
| (a) Luminous object | (iii) Emits its own light |
| (b) Transparent object | (iv) Allows all light to pass through |
| (c) Opaque object | (ii) Blocks all light |
| (d) Translucent object | (i) Allows some light to pass through |
Multiple Choice Questions (MCQs)
MCQ 1
Which property of light explains the formation of a shadow?
(a) Light travels in straight lines ✓ (b) Light has different colours ✗ (c) Light can be reflected ✗ (d) Light travels at high speed ✗
Shadows are formed because light travels in straight lines (rectilinear propagation). When an opaque object blocks the straight path of light, a shadow is formed behind it.
MCQ 2
An object that allows light to pass through partially is called:
(a) Transparent ✗ (b) Opaque ✗ (c) Translucent ✓ (d) Luminous ✗
Translucent objects allow some light to pass through but not enough to see clearly. Examples: frosted glass, butter paper, wax paper.
MCQ 3
The image formed in a pinhole camera is:
(a) Upright and virtual ✗ (b) Inverted and real ✓ (c) Upright and real ✗ (d) Inverted and virtual ✗
The pinhole camera forms a real image (can be projected on a screen) that is inverted (upside down) because light travels in straight lines.
MCQ 4
Which of the following is NOT a luminous object?
(a) Sun ✗ (b) Candle flame ✗ (c) Moon ✓ (d) Star ✗
The moon does not emit its own light. It reflects sunlight. The sun, candle flame, and stars all emit their own light and are luminous.
MCQ 5
If you hold a rectangular cardboard near a light source, the shadow formed will be:
(a) Always rectangular ✗ (b) Always circular ✗ (c) Depends on the orientation of the cardboard ✓ (d) No shadow will be formed ✗
The shape of the shadow depends on how the object is held relative to the light source. If the flat face faces the light, the shadow is rectangular. If an edge faces the light, the shadow is a thin line.
MCQ 6
A solar eclipse occurs when:
(a) The Earth comes between the Sun and the Moon ✗ (b) The Moon comes between the Sun and the Earth ✓ (c) The Sun comes between the Earth and the Moon ✗ (d) None of the above ✗
During a solar eclipse, the Moon blocks sunlight from reaching part of the Earth, casting a shadow on the Earth's surface.
Common Mistakes
1. Calling the moon a luminous object: The moon does not produce its own light. It only reflects sunlight. The moon is a non-luminous object, just like a mirror or a wall.
2. Confusing translucent and transparent: Transparent objects allow all light through (clear glass), while translucent objects allow only some light through (frosted glass). The key difference is whether you can see through the object clearly.
3. Thinking a shadow shows details of the object: A shadow only shows the outline (silhouette) of the object. It does not show the colour, surface details, or internal features. Only reflection (in a mirror) shows details.
4. Believing a pinhole camera forms an upright image: The image in a pinhole camera is always inverted (upside down). This is because light travels in straight lines — rays from the top cross over and reach the bottom of the screen.
5. Assuming a mirror produces its own light: A mirror only reflects light that falls on it. In a completely dark room, you cannot see anything in a mirror because there is no light to reflect. The mirror is not a source of light.
Exam Checklist
- [ ] Can you define and give examples of luminous and non-luminous objects?
- [ ] Can you classify materials as transparent, translucent, or opaque?
- [ ] Can you explain how a shadow is formed and list the three conditions needed?
- [ ] Can you describe how a pinhole camera works and state the nature of the image?
- [ ] Can you explain the rectilinear propagation of light and its consequences?
- [ ] Can you distinguish between a shadow and a reflection?
- [ ] Can you explain why light travels in straight lines with examples?
- [ ] Can you solve MCQs about eclipses, pinhole cameras, and properties of light?