Extra 20 important long questions and answers from Chapter:11 Light, Shadows, and Reflections of Class 6 Science (CBSE):-
1. What is light? What are its properties?
Answer: Light is a form of energy that enables us to see objects. It travels in a straight line.
Properties of light:
Light always travels in a straight line (rectilinear propagation).
It does not need a medium to travel.
Light can be reflected by shiny surfaces.
It can be absorbed by dark surfaces.
Light enables us to see non-luminous objects by reflecting off them.
2. What are luminous and non-luminous objects? Give examples.
Answer:
Luminous objects
: Objects that emit their own light. Example: Sun, candle, torch, firefly.
Non-luminous objects
: Objects that do not emit light but are visible when light falls on them. Example: Moon, table, book.
3. Explain the difference between transparent, translucent, and opaque objects with examples.
Answer:
Transparent objects
: Allow light to pass through completely. Example: Clear glass, water.
Translucent objects
: Allow some light to pass but not clearly. Example: Frosted glass, butter paper.
Opaque objects
: Do not allow any light to pass through. Example: Wood, metal.
4. What are the characteristics of a shadow?
Answer:
A shadow is always black, regardless of the object’s
colour
.
It is formed on the opposite side of the light source.
The shape of the shadow depends on the shape of the object.
The size of the shadow depends on the distance between the object and the light source.
Shadows are sharp when the light source is small and blurry when the light source is large.
5. Why does a shadow form? What are the necessary conditions for shadow formation?
Answer: A shadow forms when an opaque object blocks light.
Conditions for shadow formation:
There must be a
light source
(like the Sun, torch, or bulb).
There must be an
opaque object
to block the light.
A
surface or screen
is needed where the shadow is formed.
6. Why do shadows change size during the day?
Answer:
In the morning and evening, the Sun is low in the sky, and shadows are
long
.
At noon, the Sun is overhead, and shadows are
short
.
The angle of the light source determines the shadow’s length.
7. What is reflection of light? What are its types?
Answer: Reflection is the bouncing back of light when it hits a smooth surface.
Types of Reflection:
Regular Reflection
– Light reflects in a specific direction from a smooth surface (e.g., a plane mirror).
Irregular Reflection
– Light scatters in different directions from a rough surface (e.g., wall, paper).
8. What are the differences between a shadow and an image?
Answer:
|
Feature |
Shadow |
Image |
|---|---|---|
|
Colour |
Always black |
Same as object |
|
Shape |
Same as object, but can change in size |
Exact replica of the object |
|
Formation |
Forms when light is blocked |
Forms due to reflection or refraction |
|
Details |
No details are visible |
Shows details like colour, features |
9. How does a plane mirror form an image?
Answer: A plane mirror reflects light and forms a virtual, erect, and laterally inverted image of the object.
Characteristics of the image formed in a plane mirror:
Virtual (cannot be captured on a screen).
Erect (upright).
Same size as the object.
Laterally inverted (left appears right and vice versa).
10. What is a pinhole camera? How does it work?
Answer: A pinhole camera is a simple device that forms an inverted image of an object using a tiny hole.
Working:
Light from the object passes through the small hole.
It travels in a straight line and forms an
inverted image
on the screen.
The image is smaller and clearer when the hole is tiny.
11. How do we see objects around us?
Answer:
Light from a source (like the Sun or a bulb) falls on objects.
Some of the light is reflected by the object.
The reflected light enters our eyes.
Our brain processes the image formed in the eyes.
If there is no light, we cannot see objects.
Non-luminous objects become visible only when they reflect light.
12. How does the position of an object affect its shadow?
Answer:
When an object is
closer
to the light source, its shadow is
larger
.
When an object is
farther
from the light source, its shadow is
smaller
.
The
angle of the light source
changes the shape and direction of the shadow.
Shadows are longest during
morning and evening
due to the low Sun position.
Shadows are shortest at
noon
when the Sun is directly overhead.
Moving the object sideways can shift the shadow’s position.
13. Why do some objects form clear shadows while others form faint shadows?
Answer:
Opaque objects
form
dark and clear shadows
because they completely block light.
Translucent objects
form
faint shadows
as they allow partial light to pass.
Transparent objects
do not form shadows since they allow all light to pass.
The intensity of the light source affects the shadow’s clarity.
The distance between the object and the light source also affects shadow clarity.
A smaller light source creates sharper shadows, while a larger source makes them blurry.
14. Why do we see reflections in water, glass, and mirrors?
Answer:
Smooth and shiny surfaces reflect light in a uniform direction.
Plane mirrors
reflect light regularly, forming clear images.
Water and glass
reflect some light but also allow light to pass through.
The reflection in still water is clearer than in moving water.
When light hits a mirror, it follows the law of reflection (angle of incidence = angle of reflection).
Reflected images in a mirror appear
laterally inverted
.
15. How does a solar eclipse occur? Explain its types.
Answer:
A solar eclipse happens when the
Moon comes between the Earth and the Sun
, blocking sunlight.
It occurs only during a
new moon phase
.
Types of Solar Eclipses:
Total solar eclipse
: The entire Sun is blocked by the Moon.
Partial solar eclipse
: Only part of the Sun is blocked.
Annular solar eclipse
: The Moon covers the Sun’s
centre
, leaving a ring of light visible.
It is unsafe to look directly at a solar eclipse without protective glasses.
The eclipse is visible only in certain regions where the Moon’s shadow falls.
Solar eclipses are rare events and do not happen every month.
16. How does a lunar eclipse occur? Explain its types.
Answer:
A lunar eclipse occurs when the
Earth comes between the Sun and the Moon
, blocking sunlight from reaching the Moon.
It happens only during a
full moon
.
Types of Lunar Eclipses:
Total lunar eclipse
: The Moon is completely in Earth’s shadow.
Partial lunar eclipse
: Only part of the Moon enters Earth’s shadow.
Penumbral lunar eclipse
: The Moon moves through the faint outer shadow of Earth.
A lunar eclipse can be seen from a larger part of the world compared to a solar eclipse.
The Moon appears reddish during a total lunar eclipse due to
Rayleigh scattering
.
Unlike a solar eclipse, a lunar eclipse is safe to observe with the naked eye.
17. Why do objects appear different in size and shape in water?
Answer:
When light passes from air to water, it bends (refraction).
Due to refraction, objects appear
bigger and closer
in water.
The bending of light makes a straight object, like a pencil in water, appear
bent or broken
.
This effect is more noticeable when looking at objects at an angle.
The change in speed of light in water compared to air causes this distortion.
This principle is used in
lenses and optical instruments
.
18. What are the differences between a plane mirror and a pinhole camera image?
Answer:
|
Feature |
Plane Mirror Image |
Pinhole Camera Image |
|---|---|---|
|
Nature |
Virtual and erect |
Real and inverted |
|
Size |
Same as the object |
Smaller than the object |
|
Inversion |
Laterally inverted |
Not laterally inverted |
|
Can be captured? |
No, cannot be formed on a screen |
Yes, can be formed on a screen |
|
Clarity |
Clear and sharp |
Slightly blurred |
|
Used in |
Mirrors, periscopes |
Basic photography, experiments |
19. How do different surfaces affect the reflection of light?
Answer:
Smooth and shiny surfaces
(like mirrors) cause
regular reflection
, where light rays reflect in the same direction.
Rough surfaces
(like walls, paper) cause
irregular reflection
, where light scatters in different directions.
Polished metals
(like
aluminium
, silver) reflect most light, making them useful in mirrors and solar reflectors.
Dark or rough materials
absorb most light and reflect little, making them appear less shiny.
Water and glass
reflect some light but also allow some light to pass through, making reflections less sharp.
Reflection is used in devices like
mirrors, periscopes, telescopes, and optical instruments
.
20. How can we use mirrors to change the direction of light? Explain with an example.
Answer:
Light follows the
law of reflection
, meaning it bounces back at the same angle it strikes the mirror.
By placing a
plane mirror at an angle
, we can change the direction of light.
Example:
In a periscope, two mirrors are placed at
45-degree angles
to reflect light from an object around a barrier.
This method is used in submarines, tanks, and tall buildings to see objects from hidden positions.
Reflecting light is also useful in
solar cookers, torches, and headlights
.
A dentist’s mirror uses reflection to examine teeth more clearly.
