The natural source of light is :
- candle flame
- electric lamp
- sun
- kerosene lamp
Answer
sun
Reason — The sun is the main natural source of light.
The formation of inverted image in a pin hole camera shows that:
- light enables us to see
- light travels in a straight line path
- light can pass through the pin hole
- light does not pass through the pin hole
Answer
light travels in a straight line path
Reason — The inverted image formed in a pinhole camera is due to the fact that light rays from the top and bottom of the object travel in straight lines through the tiny pinhole and cross over to form an upside-down (inverted) image on the screen inside the camera. This clearly demonstrates that light travels in a straight line path.
The luminous body is :
- a lighted bulb
- earth
- moon
- table
Answer
a lighted bulb
Reason — The bodies which emit their own light are called luminous bodies. So, from given options a lighted bulb is the only objects which can produce its own light.
Umbra is a region of :
- complete darkness
- partial darkness
- complete brightness
- partial brightness
Answer
complete darkness
Reason — Umbra is the portion of shadow where no light reaches from the source of light due to the opaque object. It is completely dark.
Penumbra is a region of :
- complete darkness
- complete brightness
- partial brightness
- none of the above
Answer
partial brightness
Reason — Penumbra is the portion of shadow where a portion of light from the source of light reaches the shadow even in the presence of the opaque object in between them. It is not completely dark, but is dim (or less bright).
Solar eclipse occurs on :
- every new moon's day
- certain new moon's day
- every full moon's day
- certain full moon's day
Answer
certain new moon's day
Reason — A solar eclipse can only occur on a new moon day, because that's when the Moon comes between the Earth and the Sun. Hence, a solar eclipse occurs only on certain new moon days when the Sun, Moon, and Earth are in a straight line.
Lunar eclipse occurs on :
- every full moon's night
- certain full moon's night
- every new moon's day
- certain new moon's day
Answer
certain full moon's night
Reason — Lunar eclipse occurs on a certain full moon night, when the earth comes in between the sun and the moon, the earth casts its shadow on the moon.
Grease paper is an example of ............... object.
- translucent
- transparent
- opaque
- all of these
Answer
translucent
Reason — Grease paper is translucent as it allows only a part of light to pass through it
The shadow of an object does not show :
- the outline of the object
- the colour of the object
- the shape of the object
- none of these
Answer
the colour of the object
Reason — A shadow is formed when an object blocks light and it appears dark regardless of the object's actual colour so the shadow only shows the outline and shape, not the colour or details.
We do not get a shadow when
- there is an opaque object
- there is no light
- there is a light source
- there is a translucent object
Answer
there is no light
Reason — A shadow is formed when an opaque object blocks light from a source. However, if there is no light, there is nothing to block and hence, no shadow is formed. Light is essential for the formation of shadows.
Fill in the blanks :
(a) Light gives us the sensation of ............... .
(b) The sun is a ............... source of light.
(c) A medium through which light cannot pass is called the ............... .
(d) A medium which allows light to pass through it easily is called the ............... .
(e) Moon is a ............... body.
(f) Light travels in a ............... path.
(g) In a pin hole camera, the image formed is ............... .
(h) The darkest portion of a shadow is called the ............... .
(i) The less dark portion of a shadow is called the ............... .
(j) Lunar eclipse occurs when the ............... comes in between the ............... and the sun.
Answer
(a) Light gives us the sensation of vision .
(b) The sun is a natural source of light.
(c) A medium through which light cannot pass is called the opaque medium .
(d) A medium which allows light to pass through it easily is called the transparent medium .
(e) Moon is a non-luminous body.
(f) Light travels in a straight line path.
(g) In a pin hole camera, the image formed is inverted and real .
(h) The darkest portion of a shadow is called the umbra .
(i) The less dark portion of a shadow is called the penumbra .
(j) Lunar eclipse occurs when the earth comes in between the moon and the sun.
Write true or false for each statement :
(a) The moon is a natural source of light.
(b) The moon is self luminous.
(c) We can see an object through an opaque medium.
(d) Light passes through glass.
(e) Light travels in a straight line path.
(f) Image formed in a pin hole camera is real.
(g) The image in a pin hole camera gets blurred if the hole is made bigger.
(h) A shadow is formed because light travels in a straight line path.
(i) Solar eclipse occurs when the sun comes in between the earth and the moon.
(j) If the shadow of earth falls on the moon, the eclipse is called lunar eclipse.
Answer
(a) False because the moon is not a natural source of light.
(b) False since the moon does not emit light by it's own, but become visible (or shine) by the light falling on it from the sun.
(c) False as an opaque medium does not allow any light to pass through it so we cannot see the objects through an opaque medium.
(d) True because glass is a transparent medium as light can pass through it easily.
(e) True since light always travels in a straight line path so this motion of light in a straight line path is called the rectilinear propagation of light.
(f) True as characteristics of the image formed by the pin hole camera are :
- It is real i.e., it is formed on the screen.
- It is inverted or upside down.
- It is generally smaller in size than the object (because the object is far away from the pin hole than the screen).
(g) True because a bigger hole is equivalent to a large number of pin holes where each pin hole produces one image and these images overlap each other resulting in a blurred image.
(h) True as the rays which fall on the object, are blocked and they do not reach the screen. Thus, a portion on the screen does not receive any light and remains dark. This dark portion on the screen is called the shadow of the object.
(i) False because solar eclipse occurs on a certain new moon's day, when the moon comes in between the sun and the earth, the moon casts its shadow on the earth
(j) True since lunar eclipse occurs on a certain full moon night, when the earth comes in between the sun and the moon, the earth casts its shadow on the moon. The part of the moon which lies within the umbra of earth, will not be visible from the earth. Thus, the lunar eclipse takes place.
Match the following columns :
| Column A | Column B | ||
|---|---|---|---|
| (a) | Wooden block | (i) | new moon's day |
| (b) | Sun | (ii) | rectilinear propagation of light |
| (c) | Umbra | (iii) | opaque body |
| (d) | Eclipse | (iv) | luminous body |
| (e) | Solar eclipse | (v) | complete dark part |
Answer
| Column A | Column B | ||
|---|---|---|---|
| (a) | Wooden block | (iii) | opaque body |
| (b) | Sun | (iv) | luminous body |
| (c) | Umbra | (v) | complete dark part |
| (d) | Eclipse | (ii) | rectilinear propagation of light |
| (e) | Solar eclipse | (i) | new moon's day |
What is light ? Define it.
Answer
Light is a form of energy that affects our eyes to produce the sensation of vision.
How does light make an object visible ?
Answer
An object becomes visible to us when the light after striking the object gets reflected and reaches our eyes.
Name two natural sources of light.
Answer
Two natural sources of light are :
- Sun
- A firefly
List two artificial sources of light.
Answer
Two artificial sources of light are :
- Electric tubelight
- A burning candle
Differentiate between luminous and non-luminous bodies. Give two examples of each.
Answer
| Luminous bodies | Non-luminous bodies | |
|---|---|---|
| (i) | They shine and glow by their own light. | They do not emit light by their own. |
| (ii) | A luminous body becomes visible when light emitted from it reaches our eyes. | A non-luminous body becomes visible when light from a luminous body falls on it and after striking it, light reaches our eyes. |
| (iii) | Example : sun, torch. | Example : moon, earth. |
Is the moon a luminous object?
Answer
The moon is not a luminous body as it has no light of its own.
What do we call a body that shines on its own?
Answer
A body that shines on its own is called luminous body.
What do we call an electric bulb producing light?
Answer
An electric bulb producing light is called an artificial source of light.
What is a transparent medium? Give two examples.
Answer
A medium is said to be transparent if light passes through it easily so an object can be distinctly seen across a transparent substance. The examples of transparent medium are glass, air, etc.
What do we call a substance through which we cannot see light ? Give an example of such a substance.
Answer
A substance through which we cannot see light is called opaque. The examples of opaque substances are metallic sheets, black paper, etc.
What do we call a substance through which light passes? Give an example of such a substance.
Answer
A substance through which light passes is called transparent substance. The example of a transparent substance is glass.
Can a transparent medium form an image? Explain your answer.
Answer
No, a transparent medium cannot form an image because it allows light to pass through it without changing its path significantly. For an image to be formed, light needs to be redirected or blocked, which does not happen in a transparent medium.
How can you obtain a point source of light?
Answer
A point source of light is obtained either by placing a screen having a fine hole, in front of the luminous body or by placing the luminous body inside a box having a fine hole on one of its sides.
Define the terms : a ray of light and a beam of light.
Answer
Ray of light : The light travelling in any one direction in a straight line is called a ray of light.
Beam of light : A group of light rays given out from a source is called a beam of light.
What do you mean by 'rectilinear propagation of light'?
Answer
The motion of light in a straight line path is called the rectilinear propagation of light.
In which of the following two arrangements (a) and (b) shown in figure below, you can see the light of the bulb? Explain your answer.
Answer
In arrangement (a) light of the bulb can be seen because light travels in a straight line path but in arrangement (b) as the straw is bent, the light of the candle flame does not reach our eye.
Name a simple application of the rectilinear propagation of light.
Answer
Pin hole camera is a simple application of the rectilinear propagation of light.
State two factors which affect the size of image formed in a pin hole camera.
Answer
The size of an image depends on the following two factors :
- The distance of screen from the pin hole, and
- The distance of object in front of the pin hole.
Is the image obtained in a pin hole camera erect or inverted? Give reason for your answer.
Answer
The image obtained is inverted because in a pinhole camera, light rays from the top of the object pass through the tiny hole and travel in a straight line to reach the bottom of the screen inside the camera and light rays from the bottom of the object go to the top of the screen. As a result, the top becomes bottom and the bottom becomes top. So, the image is inverted (upside down).
How is the image affected in a pin hole camera when another fine hole is made near the first pin hole ?
Answer
If another pin hole is made near the first pin hole, two images are formed on the screen, one due to each of the two pin holes. If the holes are very close, the two images tend to overlap each other. As a result, a blurred image will be seen.
State the effect on the image in a pin hole camera if:
(a) the hole is made bigger.
(b) the luminous object is moved towards the pin hole.
(c) the length of the pin hole camera is increased (i.e. the screen is moved away from the pin hole).
Answer
(a) If the hole is made bigger then a blurred image is seen because a bigger hole is equivalent to a large number of pin holes and each pin hole produces one image so these images overlap each other resulting in a blurred image.
(b) If the luminous object is moved towards the pin hole i.e., the distance of object from the pin hole is decreased then the size of the image increases.
(c) On increasing the the length of the pin hole camera i.e., distance of screen from the pin hole, the size of image also increases.
What is a shadow? Give a reason for its formation.
Answer
If an opaque object is placed in front of a point source of light, it obstructs the passage of light and produces a dark patch on a screen placed behind the object. This dark patch is called the shadow of the opaque object.
The shadow is formed because light from the source travels in straight lines.
State two differences between an umbra and a penumbra.
Answer
| Umbra | Penumbra | |
|---|---|---|
| (i) | It is the portion of shadow where no light reaches from the source of light due to the opaque object. | It is the portion of shadow where a portion of light from the source of light reaches the shadow even in the presence of the opaque object in between them. |
| (ii) | It is completely dark. | It is not completely dark, but is dim (or less bright). |
Why is it that the birds flying in the sky do not cast their shadows on the earth ?
Answer
The birds flying in the sky do not cast their shadows on the earth because in their shadow, the umbra is absent and the penumbra is too large and too faint that it is not visible as the distance of earth (i.e, screen) is very large from the bird (i.e, object).
Why are shadows at noon shorter than in the morning or in the evening?
Answer
Shadows are shorter at noon because the sun is directly overhead or nearly so. This causes the sunlight to fall vertically on objects, resulting in shorter shadows.
What is an eclipse? Name the two types of eclipses.
Answer
As the sun is bigger in size than the earth and the earth is bigger in size than the moon so when the sun, the earth and the moon come in a straight line, the earth or the moon whichever comes in between, casts its shadow on the other and causes an eclipse.
Two types of eclipses are :
- Lunar eclipse
- Solar eclipse
When does a lunar eclipse take place ? Does it occur on every full moon's night?
Answer
When the earth comes in between the sun and the moon, the earth casts its shadow on the moon and the part of the moon which lies within the umbra of earth, will not be visible from the earth. Thus, the lunar eclipse takes place.
No, lunar eclipse does not occur on every full moon's night because the Moon's orbit is slightly tilted with respect to Earth's orbit. Due to this tilt, the Sun, Earth, and Moon do not always line up perfectly in a straight line during every full moon.
When does a solar eclipse take place ? Does it occur on every new moon's day?
Answer
When the moon comes in between the sun and the earth, the moon casts its shadow on the earth and in the part of the earth which lies in the umbra of the moon, the sun is not visible. Thus, total solar eclipse occurs.
No, solar eclipse does not occur on every new moon's day because the Moon's orbit is slightly tilted with respect to Earth's orbit. Due to this tilt, the Sun, Earth, and Moon do not always line up perfectly in a straight line during every new moon's day.
Explain the difference between a transparent, a translucent and an opaque medium. Give two examples of each.
Answer
| Transparent Medium | Translucent Medium | Opaque Medium | |
|---|---|---|---|
| (i) | A medium is said to be transparent if light passes through it easily. | A medium is said to be translucent if it allows only a part of light to pass through it. | A medium is said to be opaque if it does not allow any light to pass through it. |
| (ii) | The object can be distinctly seen across a transparent medium. | The details of an object cannot be distinctly seen through a translucent medium, but only a faint impression is seen. | The object cannot be seen through an opaque medium. |
| (iii) | Example : glass, water. | Example : ground glass, tracing paper. | Example : wooden screen, metallic sheets. |
Describe an experiment to show that light travels in a straight line path.
Answer
Experiment :
Place a lighted candle on a table. Take a drinking straw. Close one eye and look at the candle flame through the straw from the other eye. The flame is clearly visible.
Now, bend the straw in the middle and again look at the candle flame through the straw. The flame is not visible now. The reason is that light travels in a straight line path. When the straw is bent, the light of the candle flame does not reach our eye.
Conclusion : Light travels in a straight line path.
What is a pin hole camera? Draw a neat and labelled diagram to show the formation of image of a lighted candle by it.
Answer
A pin hole camera is a simple camera without a lens that uses a tiny hole to project an inverted image of an object onto a screen or surface inside a dark box. It works on the principle of rectilinear propagation of light.
Below is a labelled diagram of pin hole camera to show how it works :
Explain the formation of image of a luminous object in a pin hole camera with the aid of a neat diagram.
Answer
Working and formation of image :
If a luminous object AB, such as a lighted candle, is placed in front of the pin hole, an inverted picture A'B' of the candle is obtained on the tracing paper. This picture A'B' is called the image. The image obtained is upside down (i.e. inverted). The reason is that light travels in a straight line path. Hence, light from the upper point A of the candle passes through the pin hole and strikes the tracing paper at A'. Similarly, light from the lower point B of the candle passes through the pin hole and strikes the tracing paper (or screen) at B'. Light rays from all the other points between A and B, on passing through the pin hole strike the tracing paper in between A' and B'. As a result, an inverted image of the candle is seen on the tracing paper.
Below figure shows the simple ray diagram for the formation of image :
Draw a ray diagram to show the formation of shadow of an opaque object by a point source of light. How is the size of shadow affected if the screen is moved away from the object?
Answer
Below ray diagram shows the formation of shadow of an opaque object by a point source of light :
If the screen is moved away from the object the size of shadow increases, this happens because the light rays continue to diverge after passing the edges of the object.
Draw a ray diagram to show the formation of umbra alone.
Answer
Below is the ray diagram to show the formation of umbra alone :
Draw a ray diagram to show the formation of umbra and penumbra both. Label the parts umbra and penumbra in your diagram.
Answer
Below is the ray diagram to show the formation of umbra and penumbra both :
State the conditions when only the penumbra of an opaque object is obtained on the screen.
Answer
Conditions for obtaining penumbra of an opaque object are :
The light source must be extended (i.e., not a point source). Examples : tube light, the Sun, or a bulb.
Size of source of light must be bigger than the size of the opaque object.
The opaque object should be very close to the light source, and
The screen must be placed far away from the object and close to the edge of the shadow region.
In each of the following diagrams, draw rays to form umbra and penumbra on the screen.
Answer
(a)
(b)
Draw a diagram to show the formation of lunar eclipse.
Answer
Diagram showing the formation of lunar eclipse is given below:
Draw a diagram to show the formation of solar eclipse.
Answer
Diagram showing the formation of solar eclipse is given below :
What is annular solar eclipse? Draw a labelled diagram to show its formation.
Answer
An annular solar eclipse occurs when only the tip of the umbra of the moon falls on the earth at a point so that the sun will appear to be completely obstructed by the moon, only the outer rim of the sun, called corona, is then visible for a very short time which is known as the diamond ring.
The formation of annular solar eclipse is shown in below figure :
In the diagram below empty boxes show the different phases of moon as viewed from the earth. Which of the box represents the new moon?
Answer
Box D represents the new moon. This is because during a New Moon, the Moon lies between the Earth and the Sun, with its illuminated side facing away from the Earth. As a result, the Moon is not visible from Earth. A solar eclipse can also occur during this phase, but only when the Sun, Moon, and Earth are exactly aligned.
Can an object have more than one shadow? If yes, write down the possible reasons.
Answer
Yes, an object can have more than one shadow. This happens because of the following reasons:
More than one light source – If there are two or more lights shining from different directions (like two bulbs), each light makes its own shadow. So, we can see more than one shadow of the same object.
Different angles of light – When lights are placed at different angles, the shadows fall in different directions, which creates multiple shadows.
Brightness of the light – A brighter light makes a darker and clearer shadow, while a dimmer light makes a lighter shadow. So, the shadows may also look different in darkness.