RBSE Solutions Class 6 Science Chapter 16 Light and Shadows

Question 1. Classify the following light source as natural or artificial sources in table 16.1 (Page 132)

🎯 Exam Tip: Remember that natural sources of light are those found in nature, like the sun, while artificial sources are man-made, such as a bulb or candle.

 

Activities

Activity - 1

1. Take three rectangular cardboard pieces of the same size. Punch a hole exactly in the middle of each of these three cardboard pieces.

2. Now place the cardboard pieces on a table in such a way that their holes will remain in a straight line.

3. Place a lighted candle or a glowing bulb in front of the first cardboard piece.

4. Try to see the light of the candle or the bulb from the hole of the third cardboard piece.

Question 6. Is the light of the candle or bulb visible to you?
Answer: Yes, the light is visible. This shows that light travels in a straight line.
In simple words: Yes, you can see the light.

🎯 Exam Tip: Observing light through aligned holes helps prove that light travels in a straight line, a fundamental property.

 

5. Now displace the second cardboard piece by moving it a little leftwards or rightwards.

Question 9. Is the light of the candle or bulb visible to you this time?
Answer: No, the light is not visible anymore. When the second cardboard piece is moved, the straight path of light is blocked.
In simple words: No, you cannot see the light now.

🎯 Exam Tip: Understanding why the light is blocked after displacement reinforces the concept of light's linear propagation.

 

Question 11. Why is it so?
Answer: When all three holes are in a straight line, light can travel through them and reach your eyes. However, when the second cardboard piece is moved, it blocks the light's straight path, so the light cannot pass through and does not reach your eyes. This activity clearly demonstrates that light always travels in a straight path.
In simple words: Light travels in a straight line. When one cardboard piece moves, it breaks the straight line, so the light cannot reach your eyes.

🎯 Exam Tip: Explaining that light cannot bend around objects is key to describing its rectilinear propagation.

 

Question 2. What exactly are shadows? What are the requirements for their formation.
Answer: Shadows form when light hits an object that blocks it completely (an opaque object). The dark area created on a surface behind the object, where light cannot reach, is called a shadow. Shadows always form on the opposite side of the light source. For a shadow to form, three things are needed: a source of light, an opaque object, and a screen or surface for the shadow to appear on.
In simple words: Shadows are dark shapes made when an object blocks light. You need light, an object that stops light, and a surface for the shadow to appear.

🎯 Exam Tip: Clearly state the three essential requirements for shadow formation: light source, opaque object, and screen.

 

Activity - 2 (Page 133)

1. Take a piece of straight plastic pipe.

2. Light a candle and fix it on the table. From some distance, try to see the candle through the plastic pipe.

3. Now, standing at the other end of the room, look at the candle through the pipe. You will be able to see it.

Question 1. Are you still able to see the candle?
Answer: No, if you bend the pipe, you will not be able to see the candle. This is because light cannot travel through bent paths; it always moves in a straight line. So, the bent pipe blocks the light.
In simple words: No, you cannot see the candle if the pipe is bent. Light only travels straight.

🎯 Exam Tip: This experiment reinforces the concept of rectilinear propagation of light using a simple bent pipe.

 

Activity - 3

Collect everyday objects like glass, textbooks, cardboard, plates, spectacles, etc. Try to look at a glowing electric bulb through all of these objects one by one.

Question 1. Are you able to see the glowing bulb through all these objects?
Answer: No, we cannot see the glowing bulb clearly through all objects. We can see the bulb through objects like glass and spectacles. Some objects, like cardboard or a textbook, completely block the light, so we cannot see through them at all. Other objects, like certain types of plastic or thin paper, allow some light to pass, but the bulb might not be seen clearly.
In simple words: No, you can't see the bulb through everything. Some things let you see it clearly (like glass), some let you see it a little (like frosted glass), and some block it completely (like wood).

🎯 Exam Tip: This activity helps classify objects into transparent, translucent, and opaque based on how they interact with light.

 

Activity - 4

Take a sheet of paper and see a glowing electric bulb through it.

Question 1. Are you able to see the bulb clearly?
Answer: No, you will likely not be able to see the bulb clearly. A regular sheet of paper is often opaque or translucent, meaning it either blocks most light or scatters it, preventing a clear view.
In simple words: No, the bulb will not look clear through a plain paper sheet.

🎯 Exam Tip: Note the difference between seeing "clearly" and just perceiving light, which helps distinguish between transparent and translucent materials.

 

Drop some drops of cooking oil or melted butter at the center of the sheet of the paper and spread it. Try to see the glowing light bulb through the center of the paper sheet.

Question 2. What do you see now?
Answer: Now, you can see the bulb more clearly than before through the oiled part of the paper. This is because the oil fills the tiny spaces between the paper fibers, making the paper more translucent and allowing more light to pass through. You still cannot see other objects clearly from the oil-dipped sheet of paper, just the light source itself.
In simple words: You can see the bulb more clearly through the oily spot. The oil makes the paper let more light pass through.

🎯 Exam Tip: Oiling paper changes its properties, making it more translucent and demonstrating how materials can affect light transmission.

 

Activity - 5

1. You can do this activity at night with your friends.

2. Light a candle and place it in a dark room. Make a shadow of your hand on a wall of the room.

3. Now remove your hand and hold a transparent glass sheet in front of the candle.

Question 1. Can you see the shadow of the glass sheet?
Answer: No, a shadow of the glass sheet will not be formed. This happens because a transparent glass sheet allows light to pass through it completely. Since no light is blocked, no dark area (shadow) is created on the wall. If you blow out the candle and try to make a shadow of your hand again, you will still not see a shadow, as a light source is absent.
In simple words: No, the glass sheet does not make a shadow because light passes straight through it. If there is no light, there is no shadow.

🎯 Exam Tip: Remember that shadows only form when an object blocks light, not when light passes through it completely.

 

Question 2. Besides these, do we need any other thing.
Answer: Yes, besides a light source and an opaque object, we also need a screen. A screen is the surface where the shadow is cast. For example, if you take a torch and a large cardboard sheet to an open field at night and ask a friend to raise their hand where there are no buildings or trees behind them, you can then shine the torch on your friend's hand. The shadow will appear on the ground or on a screen held behind the hand.
In simple words: Yes, we need a screen. A screen is the surface where the shadow appears, like a wall or the ground.

🎯 Exam Tip: Always list the three conditions for shadow formation: light source, opaque object, and a screen.

 

1. It does not mean that there is no shadow at all behind your friend's hand.

2. Ask your another friend to hold the cardboard sheet behind the hands of your friend.

Question 4. Are you able to see the shadow of your friend's hand this time?
Answer: Yes, this time the shadow of your friend's hand will be formed on the cardboard screen. We can conclude from this activity that a shadow is only seen on a screen, which can be a floor, wall, ground, building, or any other surface. These surfaces act as screens for shadows to form on. Therefore, for a shadow to form, a source of light, an opaque object in the path of light, and a screen to receive the shadow are all necessary.
In simple words: Yes, the shadow forms on the cardboard. Shadows only appear on a surface like a wall or cardboard, which acts as a screen.

🎯 Exam Tip: The presence of a screen is crucial for observing a shadow; without it, the shadow simply isn't visible.

 

Activity - 6 (Page 135)

1. Place a table near a wall in a dark room.

2. Stand a rectangular cardboard piece on the table.

3. Throw light on the cardboard piece with a torch.

4. Carefully observe the shadow formed on the wall.

Answer:
You will observe that a dark shadow is formed on the wall. This dark shadow is called the **umbra**. Around this dark shadow, you will see a lighter shadow. This lighter shadow is called the **penumbra**. These different parts of a shadow happen because the light source has a certain size, not just a single point. You can observe the umbra and penumbra of a cricket ball and a football in the same way.
In simple words: You will see a dark shadow (umbra) and a lighter shadow around it (penumbra). This is because light sources are not just tiny points.

🎯 Exam Tip: Distinguish between the umbra (the darkest part of the shadow) and the penumbra (the lighter, outer part of the shadow).

 

Exercises

Multiple Choice Questions

Question 1. Which of the following is an opaque object?
Answer: Wood
In simple words: Wood is an object that light cannot pass through.

🎯 Exam Tip: Opaque objects completely block light, preventing any visibility through them.

 

Question 2. An artificial source of light is
(a) Sun
(b) Moon
(c) Candle
(d) Star
Answer: (c) Candle
In simple words: A candle is made by people, so it is an artificial light source.

🎯 Exam Tip: Differentiate between natural light sources (like sun, stars) and artificial ones (like candles, bulbs) that are man-made.

 

Question 3. Lunar eclipse occurs on
(a) New moon night
(b) Full moon night
(c) First day of the month
(d) Second day of the month
Answer: (b) Full moon night
In simple words: A lunar eclipse always happens when the moon is full, as it is directly behind Earth.

🎯 Exam Tip: Remember that a lunar eclipse is always associated with a full moon, when the Earth is between the Sun and Moon.

 

Question 4. Which of the following is required for the formation of shadows?
(a) Light source
(b) Opaque object
(c) Screen
(d) All of the options
Answer: (d) All of the options
In simple words: To make a shadow, you need light, something to block the light, and a surface for the shadow to appear on.

🎯 Exam Tip: Always list all three components: light source, opaque object, and a screen, as they are all crucial for shadow formation.

 

Fill in the blanks

Question 1. Light travels in a ........... line.
Answer: Straight
In simple words: Light always moves in a straight path.

🎯 Exam Tip: The concept of light traveling in a straight line is called rectilinear propagation.

 

Question 2. We can only see in the .... of light.
Answer: presence
In simple words: We need light to be able to see things.

🎯 Exam Tip: Emphasize that light reflecting off objects and entering our eyes is how we perceive them.

 

Question 3. Lantern is a .... source of light.
Answer: artificial
In simple words: A lantern is a light source made by humans.

🎯 Exam Tip: Classify light sources as either natural (from nature) or artificial (man-made).

 

Question 4. Glass, air, pure water are ........... objects.
Answer: Transparent
In simple words: Glass, air, and clean water let all light pass through them.

🎯 Exam Tip: Transparent objects allow light to pass through them completely, letting us see clearly.

 

Short Answer Type Questions

Question 1. State the differences between transparent, opaque and translucent objects.
Answer: Objects can be grouped by how much light passes through them:
1. **Transparent Objects:** These are objects that allow light to travel through them easily. You can see through them clearly. Examples include clear glass, clean water, and air.
2. **Opaque Objects:** These objects do not allow any light to pass through them. You cannot see through them at all. Examples include wood, cardboard, and metals.
3. **Translucent Objects:** These objects allow some light to pass through them, but not clearly. You can see light, but the view is blurry or fuzzy. Examples include frosted glass, tracing paper, and some thin plastics. Knowing these differences helps understand how shadows are formed.
In simple words: Transparent objects let all light pass through so you can see clearly. Opaque objects block all light, so you cannot see through them. Translucent objects let some light pass, but you cannot see clearly.

🎯 Exam Tip: Clearly define each type of object with simple examples to illustrate how they interact with light.

 

Question 2. On which days a lunar and solar eclipse occurs?
Answer: A lunar eclipse happens on a full moon night. This is when the Earth comes directly between the Sun and the Moon. A solar eclipse, on the other hand, occurs on a new moon night, which is when the Moon comes directly between the Sun and the Earth. Understanding the phases of the moon is key to predicting eclipses.
In simple words: A lunar eclipse happens during a full moon. A solar eclipse happens during a new moon.

🎯 Exam Tip: Link lunar eclipses to full moons and solar eclipses to new moons; this is a common point of confusion.

 

Question 3. Draw a well labelled diagram of the event of a lunar eclipse.
Answer: A lunar eclipse happens when the Earth passes between the Sun and the Moon, blocking the Sun's light from reaching the Moon. This makes the Moon appear dark or reddish. The diagram below shows the alignment of the Sun, Earth, and Moon during a lunar eclipse, highlighting the umbra (darkest shadow) and penumbra (lighter shadow) zones created by Earth.

In simple words: The picture shows the Sun, Earth, and Moon in a line. Earth's shadow (umbra and penumbra) falls on the Moon, causing a lunar eclipse.

🎯 Exam Tip: When drawing, ensure the Earth is positioned between the Sun and the Moon, and clearly label the umbra and penumbra regions.

 

Question 4. Write the reason for the formation of shadows.
Answer: Shadows form because light travels in straight lines and certain objects block this light. When an opaque object comes in the path of light, it does not allow the light to pass through it. This blockage creates a dark area on the surface behind the object, which is what we see as a shadow. This shadow always appears on the opposite side of the light source. The reason light travels straight is a fundamental principle of optics.
In simple words: Shadows form because light travels straight and an object gets in its way, blocking the light from reaching the other side.

🎯 Exam Tip: The two main reasons for shadow formation are the rectilinear propagation of light and the presence of an opaque object.

 

Long Answer Type Questions

Question 2. State the differences between antumbra and penumbra?
Answer: When light from a source hits an opaque object, it creates a shadow that can have different parts. The **umbra** (also sometimes called antumbra in some contexts, though typically antumbra is a specific region beyond the umbra) is the darkest part of the shadow where the light source is completely blocked. No direct light from the source reaches this area. Around this very dark shadow, there is a lighter, partial shadow called the **penumbra**. In the penumbra, only part of the light source is blocked, so some light still reaches this area. This difference in shadow intensity is due to the size of the light source.
In simple words: The umbra is the darkest part of a shadow where light is totally blocked. The penumbra is the lighter part around it where only some light is blocked.

🎯 Exam Tip: Focus on the degree of darkness: umbra is full shadow (no light), penumbra is partial shadow (some light).

 

Question 3. Explain the event of a solar eclipse, Draw necessary diagrams.
Answer: A solar eclipse happens when the Moon passes directly between the Sun and the Earth. During this event, the Moon blocks the Sun's light, casting a shadow on Earth. For people standing in the darkest part of this shadow (the umbra), they see a total solar eclipse, where the Sun is completely hidden. For those in the lighter part of the shadow (the penumbra), they see a partial solar eclipse, where only a part of the Sun is covered. This celestial alignment makes the Sun temporarily disappear from view. The diagram shows the positions of the Sun, Moon, and Earth during a solar eclipse.

In simple words: A solar eclipse happens when the Moon blocks the Sun's light from reaching Earth, creating a shadow on Earth. The diagram shows the Moon between the Sun and Earth.

🎯 Exam Tip: For a solar eclipse, ensure the Moon is between the Sun and Earth, and clearly label the umbra and penumbra on Earth.

 

Practical Work

Question 1. Classify different objects according to their transparency.
Answer: We can classify objects based on how much light passes through them. Here's a table showing different types of objects and their properties:
**Apparatus required:** Mirror, glass (smooth/rough), textbook, bulb, glass tumbler, earthen pot, plastic scale, spectacles, ball, polythene bag, thin sheet of paper, oil-dripped sheet of paper, etc.
**Activity:** Keep these objects in front of your eyes one by one and try to see a glowing bulb through them.

In simple words: Objects are sorted by how much light they let through. Transparent things let all light through, translucent things let some through but not clearly, and opaque things block all light.

🎯 Exam Tip: Be ready to provide examples for each category (transparent, translucent, opaque) and explain the difference in light transmission clearly.

 

Question 1. The luminating body is
(a) Deepak
(b) Electric bulb
(c) Star
(d) Candle
Answer: (c) Star
In simple words: A star creates its own light, which makes it a luminous object.

🎯 Exam Tip: A "luminous" body is one that produces its own light, distinguishing it from objects that merely reflect light.

 

Question 2. Moon glow due to
(a) Self light
(b) Light of sun
(c) Due to earth
(d) None of the options
Answer: (b) Light of sun
In simple words: The Moon shines because it reflects light from the Sun, not because it makes its own light.

🎯 Exam Tip: Remember that the Moon is a non-luminous object; its glow comes entirely from reflected sunlight.

 

Question 3. Transparent object is
(a) Glass
(b) Air
(c) Pure Water
(d) All of the options
Answer: (d) All of the options
In simple words: Glass, air, and pure water all let light pass through easily, so you can see clearly through them.

🎯 Exam Tip: Objects are transparent if light can pass through them without much scattering or absorption.

 

Question 4. Translucent object is
(a) Light glass
(b) Dirty water
(c) Butter paper
(d) All of the options
Answer: (d) All of the options
In simple words: Light glass, dirty water, and butter paper all let some light pass through, but you cannot see clearly through them.

🎯 Exam Tip: Translucent objects allow light to pass through, but they scatter it, making objects on the other side appear blurry.

 

Very Short Answer Questions

Question 1. How we can see objects?
Answer: We see objects when light from a source hits them and then reflects off their surface into our eyes. Without light, or if light cannot reflect into our eyes, we cannot perceive the object. This process of reflection is how our eyes gather visual information.
In simple words: We see things when light bounces off them and into our eyes.

🎯 Exam Tip: The key principle is that objects are visible because they reflect light, not because they produce it (unless they are luminous).

 

Question 2. Write names of the illuminating objects.
Answer: Illuminating objects are those that produce their own light. Two common examples are:
1. Sun
2. Bulb.
The Sun is a natural source, while a bulb is artificial, both emit light.
In simple words: Illuminating objects are ones that make their own light, like the Sun and a light bulb.

🎯 Exam Tip: Use the term "luminous objects" as a synonym for "illuminating objects" and provide both natural and artificial examples.

 

Question 3. Write name of two artificial sources of light
Answer: Two examples of artificial sources of light, which are made by humans, include:
1. Electric bulb
2. Candle
These sources provide light for various human activities after sunset or in dark places.
In simple words: Two man-made light sources are electric bulbs and candles.

🎯 Exam Tip: Be able to distinguish between natural light sources (like stars) and artificial ones (like lanterns or tube lights).

 

Question 5. Write names of two opaque objects.
Answer: Opaque objects are materials that do not allow any light to pass through them. Two examples of opaque objects are:
1. Cardboard
2. Sheet of tin
These objects cast clear shadows because they completely block light.
In simple words: Two objects that block all light are cardboard and a tin sheet.

🎯 Exam Tip: Opaque objects are crucial for shadow formation because they completely absorb or reflect incident light.

 

Short Answer Type Questions

Question 1. Write some sources of light.
Answer: Light sources are things that produce light. These can be natural or artificial. Some examples of light sources include:
1. Sun (Natural)
2. Moon (Reflects light, sometimes considered a light source in daily language)
3. Electric bulb (Artificial)
4. Lantern (Artificial)
5. Candle (Artificial)
6. C.F.L (Compact Fluorescent Lamp, Artificial)
7. Tube light (Artificial)
8. LED light (Light Emitting Diode, Artificial)
These sources are vital for vision and various applications.
In simple words: Light comes from things like the Sun, Moon, electric bulbs, candles, and lamps.

🎯 Exam Tip: When asked for sources of light, try to provide a mix of both natural and artificial examples.

 

Question 2. Define the following 1. Luminous objects 2. Shadows.
Answer:
1. **Luminous Objects:** These are objects that produce or emit their own light. They do not just reflect light from other sources. An example is the Sun. These objects act as primary sources of light.
2. **Shadows:** A shadow is a dark area formed on a surface when an opaque object blocks the path of light. Shadows always appear on the opposite side of the light source from the object. This is due to light traveling in a straight line.
Understanding these terms helps in grasping basic concepts of light.
In simple words: 1. Luminous objects make their own light, like the sun. 2. Shadows are dark shapes formed when something blocks light.

🎯 Exam Tip: For definitions, provide a clear, concise explanation and a simple example for each term.

 

Long Answer Type Questions

Question 1. Explain transparent opaque and Translucent object with examples.
Answer: Objects interact with light in different ways, leading to three main categories:
1. **Transparent Object:** A transparent object allows light to pass through it completely without any obstruction. When you look through a transparent object, you can see clearly what is on the other side.
 **Examples:** Clear glass, air, clean water, and some types of plastics are all transparent. They are often used when a clear view is needed.
2. **Opaque Object:** An opaque object completely blocks light from passing through it. You cannot see through an opaque object at all because light is either absorbed or reflected by its surface.
 **Examples:** Metals, wood, cardboard, and stones are common opaque objects. These objects are essential for forming distinct shadows.
3. **Translucent Object:** A translucent object allows some light to pass through it, but the light is scattered as it goes through. This means you cannot see clearly through a translucent object; the view appears blurry or hazy.
 **Examples:** Oil-dripped paper, butter paper, tracing paper, and rough (frosted) glass are examples of translucent objects. They allow light to diffuse, creating a soft glow.
These categories help us understand how different materials behave when exposed to light.
In simple words: Transparent objects let all light pass, so you can see clearly (like clear glass). Opaque objects block all light, so you cannot see through them (like wood). Translucent objects let some light pass but make things look blurry (like butter paper).

🎯 Exam Tip: When explaining these terms, always provide clear definitions and distinct examples for each type of object.

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