NCERT Class 6th Science Chapter 8 Light, Shadows and Reflections Question Answers

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NCERT Class 6th Science Chapter 8  Light, Shadows and Reflections Question Answers

1. Rearrange the Boxes to Form a Sentence About Opaque Objects:

Ans.

        The correct arrangement of the boxes to form a meaningful sentence is:

"Opaque objects make shadows."

This sentence helps us understand that opaque objects do not allow light to pass through them and, as a result, cast shadows.

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.

Ans.

      

Opaque objects do not allow light to pass through them and hence cast shadows.

Transparent objects allow light to pass through them completely, making them clear.

Translucent objects allow light to pass through them partially, making them blurry.

Luminous objects emit their own light.

Non-Luminous objects do not emit light; they are visible only when light reflects off them.

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?

Ans.

Yes, it is possible to create a shape that gives a circular shadow if held in one way and a rectangular shadow if held in another way.

Example: A cylinder is a shape that can create such shadows.

• When a cylinder is held with its circular face facing the light source, it will cast a circular shadow.
• When the same cylinder is held with its curved side facing the light source, it will cast a rectangular shadow.

This phenomenon occurs because the shadow of an object depends on its orientation relative to the light source.

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?

Ans.

Reflection in a Completely Dark Room:

In a completely dark room, if you hold up a mirror in front of you, you will not see a reflection of yourself.

Explanation:

• Reflection occurs when light bounces off a surface and returns to your eyes, allowing you to see an image.
• In a completely dark room, there is no light present to reflect off the mirror. Since light is essential for visibility and reflection, you won't be able to see anything, including your reflection, in the mirror.

THINGS TO THINK ABOUT

1. Opaque objects cast shadows, isn't it? Now, if we hold a transparent object in the Sun, do we see anything on the ground that gives us a hint that we are holding something in our hand?

Ans.

Yes, opaque objects cast shadows because they block light from passing through them. But what happens if we hold a transparent object in the Sun?

Explanation:

• Transparent objects allow light to pass through them entirely, so they do not cast a typical shadow like opaque objects do. However, if you closely observe the ground when holding a transparent object in sunlight, you might notice a faint outline or a slight difference in brightness. This faint outline is not a shadow but rather a minimal reduction in light intensity due to refraction or scattering of light as it passes through the transparent material.

• For example, if you hold a clear glass object in the sunlight, you may notice a very subtle boundary where the light is slightly less intense. This is because the glass bends and scatters some of the light passing through it, but it does not block the light entirely, so no distinct shadow forms.

2. We saw that changing colour of opaque objects does not change the colour of their shadows. What happens if we place an opaque object in coloured light? You can cover the face of a torch with a coloured transparent paper to do this. (Did you ever notice the colours of evening shadows just as the Sun is setting?)

Ans.

Effect of Coloured Light on Shadows

You observed that the colour of an opaque object does not change the colour of its shadow when placed in regular white light. But what happens if we place an opaque object in coloured light?

Explanation:

• When you shine coloured light on an opaque object, the shadow it casts will take on the colour of the light source. For example, if you cover the face of a torch with a red-coloured transparent paper and shine it on an opaque object, the shadow formed will appear red. This occurs because the only light available is red, and the shadow is simply an absence of light in that specific area.

• Evening Shadows: As the Sun sets, its light passes through more of Earth's atmosphere, scattering shorter blue and violet wavelengths, which gives the light a reddish or orange hue. Shadows cast during this time may appear to have a slight tint of the ambient coloured light, usually a warm hue. This is why evening shadows sometimes appear reddish or orange, reflecting the colour of the setting Sun.

So, if you place an opaque object in coloured light, the shadow will generally take on the colour of the light source because there are no other light colours to mix with or illuminate the shadowed area.