Class 6 Science

## NCERT Solution

Question 1: Rearrange the boxes given below to make a sentence that helps us understand opaque objects. OWS --- AKE --- OPAQ --- UEO --- BJEC --- TSM --- SHAD

Question 2: 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 give a circular shadow when light is incident from its top or bottom. It will give a rectangular shadow when light is incident from its side.

Question 3: 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: It is not possible to see the reflection in a mirror in a completely dark room. We need light to see anything.

Question 4: 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, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard

Transparent: Air, water, a sheet of polythene, a sheet of plane glass, a sheet of cellophane, a wire mesh

Translucent: smoke, fog

Luminous: a piece of red hot iron, a lighted fluorescent tube, the flame of a gas burner, a lighted torch, kerosene stove, 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, moon.

## Extra Questions

Question 1: What is light?

Answer: Light is a form of energy which helps us in seeing objects.

Question 2: What is the direction of propagation of light?

Answer: Light travels in a straight line.

Answer: When light falls on an opaque object, a dark patch is formed on the other side of the object; if a screen is present on the other side. This dark patch is called shadow.

Question 4: What is a luminous object?

Answer: An object which produces light is called a luminous object, e.g. sun, bulb, etc.

Question 5: What is a non-luminous object?

Answer: An object which does not produce light is called non-luminous object, e.g. moon.

Question 6: What is a transparent object?

Answer: An object which allows complete passage to light is called a transparent object. We can clearly see through a transparent object.

Question 7: What is an opaque object?

Answer: An object which does not allows passage to light is called an opaque object. We cannot see through an opaque object.

Question 8: What is a translucent object?

Answer: An object which allows partial passage to light is called a translucent object.

Question 9: Our shadows are longer in the morning and evening. Why?

Answer: During morning and evening, the angle of incident light is very small. Due to this, longer shadows are formed in the morning and evening.