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.
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.
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