Light, Shadows and Reflection

1. 
   Opaque objects make shadows.

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

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.
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.