THE GLOW OF LIGHT

      THE GLOW OF LIGHT 

Q.1. Q/A—

1.  How are objects visible to us?

Ans. Objects are visible to us only when light falling on objects is reflected. The reflected light reaches our eyes which make objects visible.

2. What happens when light falls on object?

Ans. When light falls on an object, one or more of the following three things take place-

a.    The light passes through the object.

b.   The light gets absorbed by the object.

c.    The light gets reflected by the object.

3. Why we cannot see shadow of flying aeroplane/ bird?

Ans. We cannot see it because it is so far up in the sky that its shadow is either too faint for us to see or shadow does not even reach the ground and is too fast for us to see .

4. Classify as transparent, translucent and opaque objects.

Ans. i. Air- Transparent                                  

 ii. Pure water- Transparent

iii. Ice- Transparent                                         

 iv. Thermometer- Transparent

v. Spectacles- Transparent                              

vi. Glass- Transparent

vii. Tracing paper- Translucent                   

  viii. Butter paper- Translucent

ix. Frosted glass- Translucent                        

 x. Plastic bag- Translucent

xi. Wall- Opaque                                         

 xii. Clothes- Opaque

xiii. Book—Opaque

5.   What happens to----

a. image when distance between camera and object is reduced

Ans. Image of object will become larger.

b. shadow when distance between object and source increases

Ans. Size of shadow decreases.

6. Cite an example of pinhole camera from nature.

Ans. Image of sun through the gaps in the leaves.

7. Can an object have more than one shadow?

Ans. Yes, an object can have more than one shadow. This is possible when there are more than one source of light and they are placed in different directions. Eg. In cricket field, where four light sources are placed in four directions and each player forms four shadows.

8. Using a pinhole camera a student observes the image of two of his friends, standing in sunlight, wearing yellow and red shirt respectively. What will be the colours of the shirts in the image?

Ans.  The colours of the image of the shirts will be same as the colour of the shirt.

9. You are given a transparent glass sheet. Suggest any two ways to make it translucent without breaking it.

Ans.  i. By applying oil, grease, and butter on it or pasting butter paper on it.

ii. Rubbing the surface of the glass by any abrasive material.

10. A football match is being played at night in a stadium with flood lights ON. You can see the shadow of a football kept at the ground but cannot see its shadow when it is kicked in the air. Explain.

Ans. We can see the shadow of football lying on the ground because the ground acts as a screen for it. However, when the football is kicked high, the ground, which is acting as a screen is away from the football, hence no shadow of the football will be formed on the ground.

11. List the characteristics of an image formed by a plane mirror.( Ans. Pg.no. 132)

Ans. 1. The image is of the same size and same colour as that of the object.

2. The image formed is laterally inverted.

 12. List the features of shadow.( Ans. Pg.no. 128).

Ans. 1. A shadow is formed only when the light is blocked by an opaque object.

2. A shadow is always black regardless of the colour of the object.

3. A shadow may or maynot resemble the actual shape of the object.

4. A shadow does not show the details of an object.

5. The shadow can only be formed on a screen.

6. The size of the shadow depends on

·       The shape and size of the object

·       The position of the source of light

Q 2. Define—

1. Light                                                       

2. Light Year

3. Natural source of light                       

4. Bioluminescence

5. Artificial source of light                     

 6. Rectilinear propagation of light

7. Pinhole Camera                                   

8. Eclipse

9. Reflection                                           

 10. Lateral inversion

11. Shadow—is an area of darkness created by an opaque object by not allowing light to pass through it.    

Q.3 Differences between---

a.) Luminous and non luminous objects----

	Luminous objects	Non luminous objects
1.	Objects that emit their own light.	Objects that do not emit their own light and are visible only if they reflect light from a luminous source.
2.	Eg. Sun, Lamps, Lasers, etc.	Eg. Moon, Earth, Table, etc.

b.) Transparent, translucent and opaque objects---

	Transparent  materials	Translucent materials	Opaque materials
1.	Materials that allow most of the light that falls on them to pass through them.	Materials that allow some of the light to pass through them.	Materials that do not allow  any light to pass through them
2.	Eg. Water, Glass, etc.	Eg. Butter paper, Frosted glass, etc.	Eg. Stone, rubber, etc.

c.) Image formed by plane mirror and image formed by shadow.

	Image	Shadow
1.   Colour	It has colour of object	It is always black
2.   Nature	It shows lateral inversion	Do not show lateral inversion
3.   Object description	It provides an outline as well as details of object.	It provides only outline.

d.) Solar and Lunar Eclipse with diagrams (Refer diagrams ----- pg. No. 129 TEXTBOOK).

	Solar Eclipse	Lunar Eclipse
1.	It happens when moon comes in between the sun and earth , all the three in straight line, shadow of moon fall on earth.	It happens when the earth comes in between the sun and the moon, all the three in straight line, shadow of earth falls on the moon.
2.	Sun is partially or completely blocked for some time.	In this, the moon gets partially or completely blocked for some time.
3.	Solar eclipse occurs on New moon day.	Lunar eclipse occurs on Full moon day.