NCERT TEXT BOOK EXERCISES
Q1. Rearrange the boxes given below to make a sentence that helps us understand opaque objects.
Ans.
Q2. 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.
Ans.
| 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 |
Q3. 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 ?
Ans. 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.
Q4. In a completely dark room, if you hold up a mirror in front of you, will you see your reflection in the mirror ?
Ans. 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.