Q. 1. What is light ?
Ans. Light is a form of energy which causes in us a sensation of vision.
Q. 2. What three thing can happen when light falls on an object, on the basis of which we can classify materials?
Ans. 2: When light falls on an object the following three things can happen:
(i) It is almost completely transmitted through the object.
(ii) Only a part of it may be transmitted and the rest is absorbed or spread out.
(iii) It may not at all be allowed to pass through it.
On this basis, we can classify the materials into three categories, i.e.,
(1) Transparent materials, which allow light to pass through them and through which we can see clearly are known, e.g., air, water, glass, etc.
(2) Translucent materials, through which light can pass partially and through which we cannot see clearly are called translucent materials, e.g., butter paper, coloured glass, etc.
(3) Opaque materials, which do not allow light to pass through them at all and we cannot see through them, e.g., wood, stone etc.
Q. 3. What are luminous and non-luminous bodies?
Ans. 3: All bodies which emit light energy by themselves are called luminous bodies, e.g., the sun, stars, glowing electric bulbs etc.
On the other hand, bodies such as metals, stones, trees, furniture, etc. do not emit light of their own. But they become visible if the light energy falls on them. Such bodies are called non-luminous bodies. Thus, the bodies which do not emit light energy of their own, but reflect the light energy falling on them and hence become visible are called non-luminous bodies.
Q. 4. Write down any three man-made sources of light.
Ans. 4: (i) Candle, (ii) Electric bulb, and (iii) Torch.
Q. 5. What do you understand by a beam of light. Giving examples, define—
(i) Parallel beam of light
(ii) Divergent beam of light, and
(iii) Convergent beam of light.
Ans. 5: A collection of a large number of rays of light is called a beam of light.
(i) Parallel Beam of Light. When a large number of rays travel parallel to each other, then a collection of such rays is called a parallel beam of light, e.g., the rays of sun entering a room through an open window, the rays coming out of a search light or a spot light, etc.
(ii) Divergent Beam of Light. When the rays of light starting from a point travel in various directions, then the collection of such rays is called a divergent beam of light, e.g., the rays coming out from a bulb or a car head light, etc.
(iii) Convergent Beam of Light. When the rays of light coming from different directions meet at a point, then such a collection of rays is called a convergent beam of light, e.g., if a parallel beam is made to pass through hand lens, it meets at a point, i.e., it converges at a point.
Q. 6. What do you mean by point source of light and extended source of light ?
Ans. 6: A source of light which is of the size of the head of a common pin is called point source of light. On the other hand, any source of light which is bigger than the point source of light is called an extended source of light, etc.
Q. 7. Define optical medium. What is:
(i) Homogeneous medium
(ii) Heterogeneous medium ?
Give examples.
Ans.7: Anything through which light energy can pass partially or whooly is called an optical medium.
(i) Homogeneous medium. An optical medium which has a uniform composition throughout is called homogeneous medium, e.g., diamond, glass, distilled water, pure alcohol, vacuum, etc.
(ii) Heterogeneous medium. An optical medium which has different composition at different points is called heterogeneous medium, e.g., air, muddy water, fog, smoke, etc.
Q. 8. Mention any five everyday phenomena which suggest that light travels in a straight line.
Ans. 8: There are a number of everyday fine everyday phenomena which suggest that light travels in straight lines:
(1) Formation of shadows.
(2) Formation of day and night. If light were not travelling in a straight line, then it would have curved around the earth and there would have been sunlight during night too.
(3) The beam of light coming from the projection room in the cinema hall.
(4) When the head light of a car is switched on, the light rays appear to travel in straight lines.
(5) The light coming from small laser torches, used as pointers.
All these phenomenon suggest that light travels in a straight line.
Q. 9. Why are moon and the planets visible to us even though they are not luminous ?
Ans. 9: It is because they reflect the sunlight that falls on them.
Q. 10. Rearrange the boxes given below to make a sentence that helps us understand about Opaque objects.
OWS AKE OPAQ UE O BJEC TS M SHAD
Ans. OPAQUE OBJECTS MAKE SHADOWS.
Q. 11. What is a mirror?
Ans. 11: A smooth shining surface, which rebounds the light back in same or in different direction is called a mirror.
Q. 12. Fill in the blanks:
(1) Glass is a .................. medium.
(2) The image formed in a plane mirror is formed as far ................. the mirror as the object is
in front of it.
(3) The angle between reflected ray and the ............... is called angle of reflection.
(4) Light is form of ................ which causes in us sensation of vision.
(5) Pinhole camera is based on ................. propagation of light.
Ans. 12: (1) Glass is a transparent medium.
(2) The image formed in a plane mirror is formed as far behind the mirror as the object is
in front of it.
(3) The angle between reflected ray and the normal is called angle of reflection.
(4) Light is form of energy which causes in us sensation of vision.
(5) Pinhole camera is based on rectilinear propagation of light.
Q. 13. Match the statements in Column A with those in Column B.
Column A Column B
(1) A body which partially allows the light to pass through it. Ray of light
(2) An optical medium which has different composition at different points. 3 x 10 raised to the power 8
(3) A body which does not allow light to pass through it. Shadow
(4) Speed of light Heterogeneous
(5) The path along which light energy travels in a given direction. Opaque
(6) A body emitting light on its own. Translucent
(7) Dark patch formed behind an opaque object. Luminous
Ans. 13:
Column A Column B
(1) A body which partially allows the light to pass through it. Translucent
(2) An optical medium which has different composition at different points. Heterogeneous
(3) A body which does not allow light to pass through it. Opaque
(4) Speed of light 3 × 10 raised to the power 8 m/s
(5) The path along which light energy travels in a given direction. Ray of light
(6) A body emitting light on its own. Luminous
(7) Dark patch formed behind an opaque object. Shadow
Q. 14. What is umbra and penumbra?
Ans. 14: The darkest part of a shadow is called umbra, and the region of a shadow
where the light does not reach from all parts of the source is called penumbra.
Q. 15. What is the cause of a fuzzy shadow?
Ans. 15: It is the penumbra region which extends in the form of fuzzy shadows.
Q. 16. State the characteristics of image formed by plane mirror?
Ans. 16: Characteristics of images formed by plane mirror are :
(1) A plane mirror forms an erect image.
(2) The image formed is of the same size as the object.
(3) The image is virtual, it can’t be obtained on a screen.
(4) The distance of image from the mirror is equal to the distance of object from the mirror.
(5) It is laterally inverted.
Q. 17. How many reflected rays can there be for a given single incident ray falling on a plane mirror?
Ans. 17: For one incident ray, there is one and only reflected ray.
Q. 18. State whether the sentences given below are correct or incorrect.
(1) Light gets reflected when it strikes a shiny surface.
(2) A torch bulb is a luminous object.
(3) Jugunu (firefly) is a living luminous body.
(4) The image formed by a plane mirror is inverted.
(5) Light travels in a curved line.
Ans. 18: (1) Correct (2) Correct (3) Correct (4) Incorrect (5) Incorrect.
Q. 19. What is the different between an image and a shadow?
Ans. 19: An image is formed when the light is reflected from a mirror or any shining object, while shadow is formed when the path of light is obstructed by an opaque body.
Image gives all the details of the object such as its size, colour, etc. On the other hand, shadow is a dark outline of an object and shows no details.
Question 1: Rearrange the boxes given below to make a sentence that helps us understand opaque objects.
Answer 1: Opaque objects make shadows.
Question 2: Classify the objects or materials given below as opaque, transparent or translucent, luminous or non-luminous:
Air, water, piece of rock, sheet of aluminium, mirror, wooden board, sheet of polythene, CD, smoke, sheet of plane glass, fog, piece of red hot iron, umbrella, lighted florescent tube, wall, sheet of carbon paper, flame of a gas burner, sheet of cardboard, lighted torch, sheet of cellophane, wire mesh, kerosene stove, sun, firefly, moon.
Answer 2:
Answer 3: When a cylinder is held in sunlight, then a circular shadow or a rectangular shadow can be obtained depending on its orientation related to the Sun.
When the top of the cylinder faces the Sun, then the shadow formed is circular. On the other hand, when the side of the cylinder faces the Sun, then the shadow formed is rectangular.
Question 4: In a completely dark room, if you hold up a mirror in front of you, will you see your reflection in the mirror?
Answer 4: An image is formed due to reflection of light by a plane mirror. In a completely dark room, there is no light present in the room. Thus, no reflection of light takes place by the mirror placed in the room. Hence, no image will get formed by a mirror in a completely dark room.
Question 1: To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Answer 1: Yes. The length of the dress can again be increased by unfolding it. Hence, this change can be reversed.
Question 2: You accidentally drop your favourite toy and break it. This is a change you did not want. Can this change be reversed?
Answer 2: No. This change cannot be reversed.
Question 4: A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Answer 4: If we draw a picture on a drawing sheet with a pencil, we can get back the original drawing sheet by erasing the drawing with an eraser. In this case, the change can be reversed.
However, if we draw with a pen, then the original drawing sheet cannot be obtained back because we cannot erase ink. Hence, in this case, the change cannot be reversed.
Question 5: Give examples to explain the differences between changes that can or cannot be reversed.
Answer 5: To explain the differences between changes that can or cannot be reversed, some examples are given below:
(i) If we inflate a balloon, the size and shape of the balloon undergoes a change. However, the original size and shape of the balloon can be obtained back by allowing the air to escape from the balloon. This means that the change that occurs by inflating a balloon can be reversed. But, if the balloon bursts after being inflated, then its original size and shape cannot be obtained back. Thus, in this case, the change cannot be reversed.
(ii) If we fold a piece of paper, then the shape and size of the paper undergoes a change. In this case, the original shape and size of the original paper can be obtained back. Thus, this change can be reversed. However, if we cut the piece of paper, the change in the shape and size of the paper cannot be reversed.
(iii) After we roll out a chapatti from a ball of dough, the chapatti can be converted back into a ball. Thus, the change occurring here can be reversed. But, if we cook the chapatti on a tawa, then it cannot be converted back into a ball of dough. Thus, the change is irreversible.
Question 6: A thick coating of Plaster of Paris (POP) paste is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilized. Can the change in POP be reversed?
Answer 6: When water is added to plaster of Paris (POP), it changes to another substance and on drying it hardens. Once the POP has hardened, its shape cannot be changed and POP cannot be obtained again in powdered form. Therefore, the change in POP cannot be reversed.
Question 7: A bag of cement lying in the open gets wet due to rain during the night. The next day, the sun shines brightly. Do you think the changes that have occurred in the cement can be reversed?
Answer 7: In this case, the changes cannot be reversed. This is because the cement that hardens up after getting wet cannot be obtained back in its original form again.
Question 1: What is a habitat?
Answer 1: A habitat is a natural environment where an organism lives. It is the natural surroundings in which an animal lives. Different plants and animals live in different habitats. For example, the habitat of a frog species is fresh water, while the habitat of a camel is a desert.
The organisms depend for their food, water, air, shelter and other needs on their habitat.
Question 2: How is a cactus adapted to survive in a desert?
Answer 2: A cactus is able to survive in the desert as it is adapted to the hot and humid conditions of the desert. To survive in a desert, the cactus has the following adaptations:
(i) It has long roots that go deep inside the soil for absorbing water.
(ii) Its leaves are present in the form of spines to prevent water loss through transpiration.
(iii) Its stem is covered with a thick waxy layer to retain water.
iv). The photosynthesis take place in stem only.
Question 3: Fill in the blanks:
(a) The presence of specific features, which enable a plant or an animal to live in a particular habitat, is called _________.
(b) The habitats of plants and animals that live on land are called _________ habitat.
(c) The habitats of plants and animals that live in water are called _________ habitat.
(d) Soil, water, and air are _________ factors of a habitat.
(e) Changes in our surrounding that makes us respond to them are called _________.
Answer 3: (a) The presence of specific features, which enable a plant or an animal to live in a particular habitat, is called adaptation.
(b) The habitats of plants and animals that live on land are called terrestrial habitat.
(c) The habitats of plants and animals that live in water are called aquatic habitat.
(d) Soil, water, and air are abiotic factors of a habitat.
(e) Changes in our surrounding that makes us respond to them are called stimuli.
Question 4: Which of the things in the following list are non-living?
Plough, Mushroom, Sewing Machine, Radio, Boat, Water Hyacinth, Earthworm
Answer 4: In the given list, the non-living things are plough, sewing machine, radio, and boat. On the other hand, mushroom, water hyacinth, and earthworms are living things.
Question 5: Give an example of a non-living thing that shows any two characteristics of living things.
Answer 5: One example of a non living thing that shows characteristics of living thing is cloud. It shows the following two properties of living things:
Its grows in size
It shows movements
Question 6: Among the non-living things listed below, which things were once a part of living things?
Butter, Leather, Soil, Wool, Electric Bulb, Cooking Oil, Salt, Apple, Rubber
Answer 6: The non-living things which were once a part of living things are butter, leather, wool, cooking oil, apple, and rubber. The sources of these non- living things are given next:
(a) Butter is made by churning milk, which is obtained from dairy animals.
(b) Leather is obtained from animal skin.
(c) Wool is a fabric made from the hair of sheep.
(d) Cooking oil is obtained from the seeds of the some plants (olive, palm, soybean, peanut, sunflower).
(e) Apple is a fruit obtained from apple tree.
(f) Rubber is obtained from the latex (colourless and milky discharge from plants) of rubber tree.
Soil, electric bulb, and salt are non-living things which were never a part of any living thing.
Question 7: List the common characteristics of living things.
Answer 7: Some common characteristics of living things are that they
(a) Require food
(b) Respire and excrete waste material
(c) Respond to stimuli (something causing a response) in their environment
(d) Reproduce to maintain their number
(e) Move from one place to another
(f) Grow and die
Question 8: Explain why speed is important for survival in the grasslands for animals that live there (Hint: There are few trees or places for animals to hide in grasslands habitat).
Answer 8: In grasslands, mainly grasses are found. Trees are very few in number.
Predators (who preys) such as lion, tiger, etc. that feed upon other animals are commonly found in grassland regions. It is very easy for these predators to locate their prey in the grass. Therefore, to protect themselves from these predators, animals adapt themselves by increasing their speed. The increased speed of the animal helps the physically weaker animals to escape their predator, thereby protecting themselves and increasing the chances of their survival.
Example: Deer runs very fast in grasslands to avoid being hunted by a lion.
Ans. Light is a form of energy which causes in us a sensation of vision.
Q. 2. What three thing can happen when light falls on an object, on the basis of which we can classify materials?
Ans. 2: When light falls on an object the following three things can happen:
(i) It is almost completely transmitted through the object.
(ii) Only a part of it may be transmitted and the rest is absorbed or spread out.
(iii) It may not at all be allowed to pass through it.
On this basis, we can classify the materials into three categories, i.e.,
(1) Transparent materials, which allow light to pass through them and through which we can see clearly are known, e.g., air, water, glass, etc.
(2) Translucent materials, through which light can pass partially and through which we cannot see clearly are called translucent materials, e.g., butter paper, coloured glass, etc.
(3) Opaque materials, which do not allow light to pass through them at all and we cannot see through them, e.g., wood, stone etc.
Q. 3. What are luminous and non-luminous bodies?
Ans. 3: All bodies which emit light energy by themselves are called luminous bodies, e.g., the sun, stars, glowing electric bulbs etc.
On the other hand, bodies such as metals, stones, trees, furniture, etc. do not emit light of their own. But they become visible if the light energy falls on them. Such bodies are called non-luminous bodies. Thus, the bodies which do not emit light energy of their own, but reflect the light energy falling on them and hence become visible are called non-luminous bodies.
Q. 4. Write down any three man-made sources of light.
Ans. 4: (i) Candle, (ii) Electric bulb, and (iii) Torch.
Q. 5. What do you understand by a beam of light. Giving examples, define—
(i) Parallel beam of light
(ii) Divergent beam of light, and
(iii) Convergent beam of light.
Ans. 5: A collection of a large number of rays of light is called a beam of light.
(i) Parallel Beam of Light. When a large number of rays travel parallel to each other, then a collection of such rays is called a parallel beam of light, e.g., the rays of sun entering a room through an open window, the rays coming out of a search light or a spot light, etc.
(ii) Divergent Beam of Light. When the rays of light starting from a point travel in various directions, then the collection of such rays is called a divergent beam of light, e.g., the rays coming out from a bulb or a car head light, etc.
(iii) Convergent Beam of Light. When the rays of light coming from different directions meet at a point, then such a collection of rays is called a convergent beam of light, e.g., if a parallel beam is made to pass through hand lens, it meets at a point, i.e., it converges at a point.
Q. 6. What do you mean by point source of light and extended source of light ?
Ans. 6: A source of light which is of the size of the head of a common pin is called point source of light. On the other hand, any source of light which is bigger than the point source of light is called an extended source of light, etc.
Q. 7. Define optical medium. What is:
(i) Homogeneous medium
(ii) Heterogeneous medium ?
Give examples.
Ans.7: Anything through which light energy can pass partially or whooly is called an optical medium.
(i) Homogeneous medium. An optical medium which has a uniform composition throughout is called homogeneous medium, e.g., diamond, glass, distilled water, pure alcohol, vacuum, etc.
(ii) Heterogeneous medium. An optical medium which has different composition at different points is called heterogeneous medium, e.g., air, muddy water, fog, smoke, etc.
Q. 8. Mention any five everyday phenomena which suggest that light travels in a straight line.
Ans. 8: There are a number of everyday fine everyday phenomena which suggest that light travels in straight lines:
(1) Formation of shadows.
(2) Formation of day and night. If light were not travelling in a straight line, then it would have curved around the earth and there would have been sunlight during night too.
(3) The beam of light coming from the projection room in the cinema hall.
(4) When the head light of a car is switched on, the light rays appear to travel in straight lines.
(5) The light coming from small laser torches, used as pointers.
All these phenomenon suggest that light travels in a straight line.
Q. 9. Why are moon and the planets visible to us even though they are not luminous ?
Ans. 9: It is because they reflect the sunlight that falls on them.
Q. 10. Rearrange the boxes given below to make a sentence that helps us understand about Opaque objects.
OWS AKE OPAQ UE O BJEC TS M SHAD
Ans. OPAQUE OBJECTS MAKE SHADOWS.
Q. 11. What is a mirror?
Ans. 11: A smooth shining surface, which rebounds the light back in same or in different direction is called a mirror.
Q. 12. Fill in the blanks:
(1) Glass is a .................. medium.
(2) The image formed in a plane mirror is formed as far ................. the mirror as the object is
in front of it.
(3) The angle between reflected ray and the ............... is called angle of reflection.
(4) Light is form of ................ which causes in us sensation of vision.
(5) Pinhole camera is based on ................. propagation of light.
Ans. 12: (1) Glass is a transparent medium.
(2) The image formed in a plane mirror is formed as far behind the mirror as the object is
in front of it.
(3) The angle between reflected ray and the normal is called angle of reflection.
(4) Light is form of energy which causes in us sensation of vision.
(5) Pinhole camera is based on rectilinear propagation of light.
Q. 13. Match the statements in Column A with those in Column B.
Column A Column B
(1) A body which partially allows the light to pass through it. Ray of light
(2) An optical medium which has different composition at different points. 3 x 10 raised to the power 8
(3) A body which does not allow light to pass through it. Shadow
(4) Speed of light Heterogeneous
(5) The path along which light energy travels in a given direction. Opaque
(6) A body emitting light on its own. Translucent
(7) Dark patch formed behind an opaque object. Luminous
Ans. 13:
Column A Column B
(1) A body which partially allows the light to pass through it. Translucent
(2) An optical medium which has different composition at different points. Heterogeneous
(3) A body which does not allow light to pass through it. Opaque
(4) Speed of light 3 × 10 raised to the power 8 m/s
(5) The path along which light energy travels in a given direction. Ray of light
(6) A body emitting light on its own. Luminous
(7) Dark patch formed behind an opaque object. Shadow
Q. 14. What is umbra and penumbra?
Ans. 14: The darkest part of a shadow is called umbra, and the region of a shadow
where the light does not reach from all parts of the source is called penumbra.
Q. 15. What is the cause of a fuzzy shadow?
Ans. 15: It is the penumbra region which extends in the form of fuzzy shadows.
Q. 16. State the characteristics of image formed by plane mirror?
Ans. 16: Characteristics of images formed by plane mirror are :
(1) A plane mirror forms an erect image.
(2) The image formed is of the same size as the object.
(3) The image is virtual, it can’t be obtained on a screen.
(4) The distance of image from the mirror is equal to the distance of object from the mirror.
(5) It is laterally inverted.
Q. 17. How many reflected rays can there be for a given single incident ray falling on a plane mirror?
Ans. 17: For one incident ray, there is one and only reflected ray.
Q. 18. State whether the sentences given below are correct or incorrect.
(1) Light gets reflected when it strikes a shiny surface.
(2) A torch bulb is a luminous object.
(3) Jugunu (firefly) is a living luminous body.
(4) The image formed by a plane mirror is inverted.
(5) Light travels in a curved line.
Ans. 18: (1) Correct (2) Correct (3) Correct (4) Incorrect (5) Incorrect.
Q. 19. What is the different between an image and a shadow?
Ans. 19: An image is formed when the light is reflected from a mirror or any shining object, while shadow is formed when the path of light is obstructed by an opaque body.
Image gives all the details of the object such as its size, colour, etc. On the other hand, shadow is a dark outline of an object and shows no details.
Saturday, September 22, 2012
Answers of Science Class VIth Chapter 11 - Light, Shadows and Reflection
Question 1: Rearrange the boxes given below to make a sentence that helps us understand opaque objects.
Answer 1: Opaque objects make shadows.
Question 2: Classify the objects or materials given below as opaque, transparent or translucent, luminous or non-luminous:
Air, water, piece of rock, sheet of aluminium, mirror, wooden board, sheet of polythene, CD, smoke, sheet of plane glass, fog, piece of red hot iron, umbrella, lighted florescent tube, wall, sheet of carbon paper, flame of a gas burner, sheet of cardboard, lighted torch, sheet of cellophane, wire mesh, kerosene stove, sun, firefly, moon.
Answer 2:
Object
|
Object is Transparent/Translucent/Opaque
|
Object is Luminous/Non-luminous
|
Air
|
Transparent
|
Non-luminous
|
Water
|
Transparent
|
Non-luminous
|
Piece of rock
|
Opaque
|
Non-luminous
|
Sheet of aluminium
|
Opaque
|
Non-luminous
|
Mirror
|
Opaque
|
Non-luminous
|
Wooden board
|
Opaque
|
Non-luminous
|
Sheet of polythene
|
Translucent
|
Non-luminous
|
CD
|
Translucent
|
Non-luminous
|
Smoke
|
Translucent
|
Non-luminous
|
Sheet of plane glass
|
Transparent
|
Non-luminous
|
Fog
|
Translucent
|
Non-luminous
|
Piece of red hot iron
|
Opaque
|
Luminous
|
Umbrella
|
Opaque
|
Non-luminous
|
Lighted fluorescent tube
|
Opaque
|
Luminous
|
Wall
|
Opaque
|
Non-luminous
|
Sheet of carbon paper
|
Opaque
|
Non-luminous
|
Flame of a gas burner
|
Translucent
|
Luminous
|
Sheet of cardboard
|
Opaque
|
Non-luminous
|
Lighted torch
|
Opaque
|
Luminous
|
Sheet of cellophane
|
Translucent
|
Non-luminous
|
Wire mesh
|
Translucent
|
Non-luminous
|
Kerosene stove
|
Opaque
|
Luminous
|
Sun
|
Opaque
|
Luminous
|
Firefly
|
Opaque
|
Luminous
|
Moon
|
Opaque
|
Non-luminous
|
Question 3: 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?
Answer 3: When a cylinder is held in sunlight, then a circular shadow or a rectangular shadow can be obtained depending on its orientation related to the Sun.
When the top of the cylinder faces the Sun, then the shadow formed is circular. On the other hand, when the side of the cylinder faces the Sun, then the shadow formed is rectangular.
Question 4: In a completely dark room, if you hold up a mirror in front of you, will you see your reflection in the mirror?
Answer 4: An image is formed due to reflection of light by a plane mirror. In a completely dark room, there is no light present in the room. Thus, no reflection of light takes place by the mirror placed in the room. Hence, no image will get formed by a mirror in a completely dark room.
Friday, September 21, 2012
Answers of Science Class 6 Chapter 6 Changes Around Us
Answer 1: Yes. The length of the dress can again be increased by unfolding it. Hence, this change can be reversed.
Question 2: You accidentally drop your favourite toy and break it. This is a change you did not want. Can this change be reversed?
Answer 2: No. This change cannot be reversed.
Question 3: Some changes are listed in the following table. For each change, write in the blank column whether the change can be reversed or not.
S. No.
|
Change
|
Can be reversed (Yes/No)
|
1.
|
Sawing of a piece of wood
|
-
|
2.
|
Melting of ice candy
|
-
|
3.
|
Dissolving sugar in water
|
-
|
4.
|
Cooking food
|
-
|
5.
|
Ripening of a mango
|
-
|
6.
|
Souring of milk
|
-
|
Answer 3:
S. No.
|
Change
|
Can be reversed (Yes/No)
|
1.
|
Sawing of a piece of wood
|
No
|
2.
|
Melting of ice candy
|
Yes
|
3.
|
Dissolving sugar in water
|
Yes
|
4.
|
Cooking food
|
No
|
5.
|
Ripening of a mango
|
No
|
6.
|
Souring of milk
|
No
|
Question 4: A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Answer 4: If we draw a picture on a drawing sheet with a pencil, we can get back the original drawing sheet by erasing the drawing with an eraser. In this case, the change can be reversed.
However, if we draw with a pen, then the original drawing sheet cannot be obtained back because we cannot erase ink. Hence, in this case, the change cannot be reversed.
Question 5: Give examples to explain the differences between changes that can or cannot be reversed.
Answer 5: To explain the differences between changes that can or cannot be reversed, some examples are given below:
(i) If we inflate a balloon, the size and shape of the balloon undergoes a change. However, the original size and shape of the balloon can be obtained back by allowing the air to escape from the balloon. This means that the change that occurs by inflating a balloon can be reversed. But, if the balloon bursts after being inflated, then its original size and shape cannot be obtained back. Thus, in this case, the change cannot be reversed.
(ii) If we fold a piece of paper, then the shape and size of the paper undergoes a change. In this case, the original shape and size of the original paper can be obtained back. Thus, this change can be reversed. However, if we cut the piece of paper, the change in the shape and size of the paper cannot be reversed.
(iii) After we roll out a chapatti from a ball of dough, the chapatti can be converted back into a ball. Thus, the change occurring here can be reversed. But, if we cook the chapatti on a tawa, then it cannot be converted back into a ball of dough. Thus, the change is irreversible.
Question 6: A thick coating of Plaster of Paris (POP) paste is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilized. Can the change in POP be reversed?
Answer 6: When water is added to plaster of Paris (POP), it changes to another substance and on drying it hardens. Once the POP has hardened, its shape cannot be changed and POP cannot be obtained again in powdered form. Therefore, the change in POP cannot be reversed.
Question 7: A bag of cement lying in the open gets wet due to rain during the night. The next day, the sun shines brightly. Do you think the changes that have occurred in the cement can be reversed?
Answer 7: In this case, the changes cannot be reversed. This is because the cement that hardens up after getting wet cannot be obtained back in its original form again.
Thursday, September 20, 2012
Answers of NCERT Science Class 6 Chapter 9 The Living Organisms and Their Surroundings
Answer 1: A habitat is a natural environment where an organism lives. It is the natural surroundings in which an animal lives. Different plants and animals live in different habitats. For example, the habitat of a frog species is fresh water, while the habitat of a camel is a desert.
The organisms depend for their food, water, air, shelter and other needs on their habitat.
Question 2: How is a cactus adapted to survive in a desert?
Answer 2: A cactus is able to survive in the desert as it is adapted to the hot and humid conditions of the desert. To survive in a desert, the cactus has the following adaptations:
(i) It has long roots that go deep inside the soil for absorbing water.
(ii) Its leaves are present in the form of spines to prevent water loss through transpiration.
(iii) Its stem is covered with a thick waxy layer to retain water.
iv). The photosynthesis take place in stem only.
Question 3: Fill in the blanks:
(a) The presence of specific features, which enable a plant or an animal to live in a particular habitat, is called _________.
(b) The habitats of plants and animals that live on land are called _________ habitat.
(c) The habitats of plants and animals that live in water are called _________ habitat.
(d) Soil, water, and air are _________ factors of a habitat.
(e) Changes in our surrounding that makes us respond to them are called _________.
Answer 3: (a) The presence of specific features, which enable a plant or an animal to live in a particular habitat, is called adaptation.
(b) The habitats of plants and animals that live on land are called terrestrial habitat.
(c) The habitats of plants and animals that live in water are called aquatic habitat.
(d) Soil, water, and air are abiotic factors of a habitat.
(e) Changes in our surrounding that makes us respond to them are called stimuli.
Question 4: Which of the things in the following list are non-living?
Plough, Mushroom, Sewing Machine, Radio, Boat, Water Hyacinth, Earthworm
Answer 4: In the given list, the non-living things are plough, sewing machine, radio, and boat. On the other hand, mushroom, water hyacinth, and earthworms are living things.
Question 5: Give an example of a non-living thing that shows any two characteristics of living things.
Answer 5: One example of a non living thing that shows characteristics of living thing is cloud. It shows the following two properties of living things:
Its grows in size
It shows movements
Question 6: Among the non-living things listed below, which things were once a part of living things?
Butter, Leather, Soil, Wool, Electric Bulb, Cooking Oil, Salt, Apple, Rubber
Answer 6: The non-living things which were once a part of living things are butter, leather, wool, cooking oil, apple, and rubber. The sources of these non- living things are given next:
(a) Butter is made by churning milk, which is obtained from dairy animals.
(b) Leather is obtained from animal skin.
(c) Wool is a fabric made from the hair of sheep.
(d) Cooking oil is obtained from the seeds of the some plants (olive, palm, soybean, peanut, sunflower).
(e) Apple is a fruit obtained from apple tree.
(f) Rubber is obtained from the latex (colourless and milky discharge from plants) of rubber tree.
Soil, electric bulb, and salt are non-living things which were never a part of any living thing.
Question 7: List the common characteristics of living things.
Answer 7: Some common characteristics of living things are that they
(a) Require food
(b) Respire and excrete waste material
(c) Respond to stimuli (something causing a response) in their environment
(d) Reproduce to maintain their number
(e) Move from one place to another
(f) Grow and die
Question 8: Explain why speed is important for survival in the grasslands for animals that live there (Hint: There are few trees or places for animals to hide in grasslands habitat).
Answer 8: In grasslands, mainly grasses are found. Trees are very few in number.
Predators (who preys) such as lion, tiger, etc. that feed upon other animals are commonly found in grassland regions. It is very easy for these predators to locate their prey in the grass. Therefore, to protect themselves from these predators, animals adapt themselves by increasing their speed. The increased speed of the animal helps the physically weaker animals to escape their predator, thereby protecting themselves and increasing the chances of their survival.
Example: Deer runs very fast in grasslands to avoid being hunted by a lion.
Saturday, September 1, 2012
Answers of Class VIth Science Chapter 7 - Getting to Know Plants
Question 1: Correct the following statements and rewrite them in your notebook.
(a) Stem absorbs water and minerals from the soil.
(b) Leaves hold the plant upright.
(c) Roots conduct water to the leaves.
(d) The number of petals and sepals in a flower is always equal.
(e) If the sepals of a flower are joined together, then its petals are also joined together.
(f) If the petals of a flower are joined together, then the pistil is joined to the petal.
Answer 1: (a) Root absorbs water and minerals from the soil.
(b) Stem holds the plant upright.
(c) Stem conducts water to the leaves.
(d) The number of petals and sepals in a flower may be different in different plants.
(e) If the sepals of a flower are joined together, then its petals may or may not be joined together.
(f) If the petals of a flower are joined together, then the stamen may or may not be joined to the petal.
Question 2: Draw (a) a leaf, (b) a taproot, and (c) a flower that you have studied for Table 7.3.
Answer 2: (a)
Leaf of a rose plant
(b)
Taproot of a rose plant
(c)
Flower of a rose plant
Question 3: Can you find a plant in your house or in your neighbourhood which has a long but a weak stem? Write its name. In which category would you classify it?
Answer 3: The money plant has a long and weak stem. It comes under the category of climbers. Climbers are plants that readily take support on neighbouring structures as they have a weak stem.
Question 4: What is the function of a stem in plant?
Answer 4: The main function of a stem in plants is that it helps in the conduction of water and minerals from the roots to the leaves and other parts of plants. It also provides support to branches, leaves, flowers, fruits, and buds of plants.
Question 5: Which of the following leaves have reticulate venation?
Wheat, tulsi, maize, grass, coriander (dhania), China rose
Answer 5: The leaves of tulsi, coriander, and China rose have reticulate venation, whereas maize, grass, and wheat have parallel venation.
In leaves with reticulate venation, the veins are arranged in a net-like pattern. In parallel venation, the veins are arranged parallel to one another.
Leaves with reticulate and parallel venation
Question 6: If a plant has fibrous roots, what type of venation are its leaves likely to have?
Answer 6: Plants with fibrous roots have parallel venation in their leaves. For example, grass, wheat, maize, etc. have fibrous roots with parallel venation.
Fibrous roots with parallel venation
Fibrous roots have thin and moderately growing branches arising from the stem. Parallel venation, on the other hand, has leaves in which the veins are arranged parallel to each other.
Question 7: If a plant has leaves with reticulate venation, then what kind of roots does it have?
Answer 7: Plants with reticulate venation in their leaves are likely to have tap roots. For example, a carrot or a rose plant has leaves with reticulate venation and its roots are called tap roots.
Taproots and reticulate venation
In tap roots, there is one main root known as the ‘tap root’ that grows straight down from the stem. It also has smaller roots known as ‘lateral roots’. In leaves with reticulate venation, the veins are arranged in a net-like pattern.
Question 8: Is it possible for you to recognize leaves without seeing them? How?
Answer 8: Yes. We can recognize leaves without seeing them. You can look for the type of roots of the plant and identify the type of leaf. If the plant has fibrous roots, then its leaves have parallel venation, and if the plant has tap roots, then its leaves have reticulate venation.
Question 9: Write the names of the parts of a flower.
Answer 9: A flower consists of sepals, petals, stamens, and pistils. A stamen has two parts called the anther and the filament. A pistil has three parts called the stigma, style, and ovary.
A flower with its part shown
Question 10: Which of the following plants have you seen? Of those that you have seen, which ones have flowers?
Grass, maize, wheat, chilli, tomato, tulsi, pipal, shisham, banyan, mango, jamun, guava, pomegranate, papaya, banana, lemon, sugarcane, potato, groundnut.
Answer 10: The given examples are flowering plants. But, in some plants such as tulsi, pipal, sugarcane, etc. the flowers are not visible. They are so small that they cannot be seen with naked eyes.
Question 11: Name that part of plants which produces food. Name this process.
Answer 11: The part of plants which prepares food is the leaf. Leaves of a plant prepare food in the presence of sunlight. The process of making food by utilizing water and carbon dioxide in the presence of sunlight is called photosynthesis.
Question 12: In which part of a flower, you are likely to find the ovary?
Answer 12: Pistil is the part of the flower that contains the ovary.
The structure of a pistil showing all its parts
Question 13: Name two flowers each with joined and separated sepals.
Answer 13: Flowers with joined sepals are Periwinkle (Sadabahar) and Hibiscus (China rose).
Flowers with separated sepals are Rose and Magnolia.
(a) Stem absorbs water and minerals from the soil.
(b) Leaves hold the plant upright.
(c) Roots conduct water to the leaves.
(d) The number of petals and sepals in a flower is always equal.
(e) If the sepals of a flower are joined together, then its petals are also joined together.
(f) If the petals of a flower are joined together, then the pistil is joined to the petal.
Answer 1: (a) Root absorbs water and minerals from the soil.
(b) Stem holds the plant upright.
(c) Stem conducts water to the leaves.
(d) The number of petals and sepals in a flower may be different in different plants.
(e) If the sepals of a flower are joined together, then its petals may or may not be joined together.
(f) If the petals of a flower are joined together, then the stamen may or may not be joined to the petal.
Question 2: Draw (a) a leaf, (b) a taproot, and (c) a flower that you have studied for Table 7.3.
Answer 2: (a)
Leaf of a rose plant
(b)
Taproot of a rose plant
(c)
Question 3: Can you find a plant in your house or in your neighbourhood which has a long but a weak stem? Write its name. In which category would you classify it?
Answer 3: The money plant has a long and weak stem. It comes under the category of climbers. Climbers are plants that readily take support on neighbouring structures as they have a weak stem.
Question 4: What is the function of a stem in plant?
Answer 4: The main function of a stem in plants is that it helps in the conduction of water and minerals from the roots to the leaves and other parts of plants. It also provides support to branches, leaves, flowers, fruits, and buds of plants.
Question 5: Which of the following leaves have reticulate venation?
Wheat, tulsi, maize, grass, coriander (dhania), China rose
Answer 5: The leaves of tulsi, coriander, and China rose have reticulate venation, whereas maize, grass, and wheat have parallel venation.
In leaves with reticulate venation, the veins are arranged in a net-like pattern. In parallel venation, the veins are arranged parallel to one another.
Leaves with reticulate and parallel venation
Question 6: If a plant has fibrous roots, what type of venation are its leaves likely to have?
Answer 6: Plants with fibrous roots have parallel venation in their leaves. For example, grass, wheat, maize, etc. have fibrous roots with parallel venation.
Fibrous roots with parallel venation
Fibrous roots have thin and moderately growing branches arising from the stem. Parallel venation, on the other hand, has leaves in which the veins are arranged parallel to each other.
Question 7: If a plant has leaves with reticulate venation, then what kind of roots does it have?
Answer 7: Plants with reticulate venation in their leaves are likely to have tap roots. For example, a carrot or a rose plant has leaves with reticulate venation and its roots are called tap roots.
Taproots and reticulate venation
In tap roots, there is one main root known as the ‘tap root’ that grows straight down from the stem. It also has smaller roots known as ‘lateral roots’. In leaves with reticulate venation, the veins are arranged in a net-like pattern.
Question 8: Is it possible for you to recognize leaves without seeing them? How?
Answer 8: Yes. We can recognize leaves without seeing them. You can look for the type of roots of the plant and identify the type of leaf. If the plant has fibrous roots, then its leaves have parallel venation, and if the plant has tap roots, then its leaves have reticulate venation.
Question 9: Write the names of the parts of a flower.
Answer 9: A flower consists of sepals, petals, stamens, and pistils. A stamen has two parts called the anther and the filament. A pistil has three parts called the stigma, style, and ovary.
A flower with its part shown
Question 10: Which of the following plants have you seen? Of those that you have seen, which ones have flowers?
Grass, maize, wheat, chilli, tomato, tulsi, pipal, shisham, banyan, mango, jamun, guava, pomegranate, papaya, banana, lemon, sugarcane, potato, groundnut.
Answer 10: The given examples are flowering plants. But, in some plants such as tulsi, pipal, sugarcane, etc. the flowers are not visible. They are so small that they cannot be seen with naked eyes.
Question 11: Name that part of plants which produces food. Name this process.
Answer 11: The part of plants which prepares food is the leaf. Leaves of a plant prepare food in the presence of sunlight. The process of making food by utilizing water and carbon dioxide in the presence of sunlight is called photosynthesis.
Question 12: In which part of a flower, you are likely to find the ovary?
Answer 12: Pistil is the part of the flower that contains the ovary.
The structure of a pistil showing all its parts
Question 13: Name two flowers each with joined and separated sepals.
Answer 13: Flowers with joined sepals are Periwinkle (Sadabahar) and Hibiscus (China rose).
Flowers with separated sepals are Rose and Magnolia.
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