Light

sun

Reason — The sun is the main natural source of light.

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.

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.

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.

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).

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.

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.

translucent

Reason — Grease paper is translucent as it allows only a part of light to pass through it

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.

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.

A is true but R is false.

Explanation:

Assertion (A) is true because the umbra is the darkest part of a shadow, where light from the source is completely blocked.

Reason (R) is false because the umbra is not formed where light is partially blocked. Partial blocking of light forms the penumbra.

Therefore, A is true but R is false.

Both A and R are true and R is the correct explanation of A

Explanation

Assertion (A) is true because a pinhole camera forms an inverted image.

Reason (R) is also true. Light travels in straight lines. Therefore, light rays from the top of the object pass through the pinhole and reach the bottom of the screen, while rays from the bottom of the object reach the top of the screen.

Thus, the Reason correctly explains why the image formed by a pinhole camera is inverted.

Therefore, both A and R are true and R is the correct explanation of A.

(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.

(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 :

1. It is real i.e., it is formed on the screen.
2. It is inverted or upside down.
3. 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.

Light is a form of energy that affects our eyes to produce the sensation of vision.

An object becomes visible to us when the light after striking the object gets reflected and reaches our eyes.

Two natural sources of light are :

1. Sun
2. A firefly

Two artificial sources of light are :

1. Electric tubelight
2. A burning candle

The moon is not a luminous body as it has no light of its own.

A body that shines on its own is called luminous body.

An electric bulb producing light is called an artificial source of light.

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.

A substance through which we cannot see light is called opaque. The examples of opaque substances are metallic sheets, black paper, etc.

A substance through which light passes is called transparent substance. The example of a transparent substance is glass.

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.

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.

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.

The motion of light in a straight line path is called the rectilinear propagation of light.

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.

Pin hole camera is a simple application of the rectilinear propagation of light.

The size of an image depends on the following two factors :

1. The distance of screen from the pin hole, and
2. The distance of object in front of the pin hole.

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).

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.

(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.

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.

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).

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.

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 :

1. Lunar eclipse
2. Solar eclipse

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 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.

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.

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 :

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 :

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.

Below is the ray diagram to show the formation of umbra alone :

(a)

(b)

Below is the ray diagram to show the formation of umbra and penumbra both :

Conditions for obtaining penumbra of an opaque object are :

1. The light source must be extended (i.e., not a point source). Examples : tube light, the Sun, or a bulb.

2. Size of source of light must be bigger than the size of the opaque object.

3. The opaque object should be very close to the light source, and

4. The screen must be placed far away from the object and close to the edge of the shadow region.

Diagram showing the formation of lunar eclipse is given below:

Diagram showing the formation of solar eclipse is given below :

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 :

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.

Yes, an object can have more than one shadow. This happens because of the following reasons:

1. 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.

2. Different angles of light – When lights are placed at different angles, the shadows fall in different directions, which creates multiple shadows.

3. 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.

(i) A shadow forms because the football is an opaque object and blocks the light from the candle, preventing some of the light from reaching the wall.
If the football is placed behind the candle, away from the wall, it will not block the light travelling from the candle to the wall. Therefore, no shadow of the football will form on that wall.

(ii) The dark central region of the shadow is the umbra. In this region, light from the candle is completely blocked.

(iii) The shadow is similar to that formed during a solar eclipse because, in both cases, an opaque object blocks light and forms umbra and penumbra. The football blocks the candlelight just as the Moon blocks sunlight during a solar eclipse.

(iv) During a solar eclipse, the Moon comes between the Sun and the Earth and blocks the Sun's light.