CHAPTER- 8 LIGHT, SHADOW AND REFLECTIONS
Notes
1. Light helps us to see objects. Without light, we cannot see objects.
2. Luminous objects– Objects that emit their own light, like the Sun, are called luminous objects.
3. Opaque– If we cannot see through an object, then it is called an opaque object.
4. Transparent– If we can see through an object, it allows light to pass through it. Such an object is called transparent.
5. Translucent– Some objects allow us to see through them, but not clearly. Such objects are called translucent.
6. Whether an object or a material is opaque, transparent, or translucent depends on how it allows light to pass through it— completely, partially, or not at all.
7. A shadow can be seen only on a screen. The ground, walls of a room, buildings, and other such surfaces act like screens for the many shadows we see in our daily life.
8. We should never look directly at the Sun. It can be extremely harmful to our eyes.
9. We see our face in a mirror; what we see is the reflection of our face in the mirror.
- We also see the reflection of objects placed in front of a mirror in the mirror.
- A mirror changes the direction of the light that falls on it.
- Light travels in a straight line and gets reflected from a mirror.
EXERCISE
Question- 2. Classify the objects or materials given below as opaque, transparent or translucent and luminous or non-luminous:
Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the flame of a gas burner, a sheet of cardboard, a lighted torch, a sheet of cellophane, a wire mesh, kerosene stove, sun, firefly, moon.
Answer- Opaque- A piece of rock, a sheet of aluminium, a mirror, a wooden board, a CD, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the flame of a gas burner, a sheet of cardboard, a lighted torch, kerosene stove, sun, firefly, moon.
Transparent- Air, Water.
Luminous- A piece of red hot iron, a lighted fluorescent tube, the flame of a gas burner, a lighted torch, sun, firefly.
Non-luminous- Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard, a sheet of cellophane, a wire mesh, kerosene stove, moon.
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- A cylindrical shape can form two kinds of shadows. When its circular top faces the light, it forms a circular shadow. When the curved side of the cylindrical shape faces the light, it forms a rectangular shadow.
Question- 4. In a completely dark room, if you hold up a mirror in front of you, will you see a reflection of yourself in the mirror?
Answer- No, we cannot see the reflection of our face in a dark room. We can see reflections only in the presence of light.