Light Shadows And Reflections - Class 6 Physics - Extra Questions

A ray of light is defined as the path along which light travels. Light travels in a rectilinear path.

Pinhole camera is based on the rectilinear propagation of light. 

For example, glass can be used to make bowls, bulbs, window panes, etc. The same object can be made of different kinds of materials. For example, a chair is made of wood, plastic, or iron. Some objects are made up of a combination of several materials.

Translucent medium - A medium through which light propagates partially is called a translucent medium E.g. - ground glass, butter paper, fog, etc.

The characteristics of image are as follows -
(i) The image formed is real hence it can be formed on the screen
(ii) It is inverted
(iii) It is generally smaller than the size of the object

Shadow - The dark patch formed behind an opaque body when it is 
placed in the path of light is called a shadow

1. Ground glass is glass whose surface has been ground produce a flat but rough finish due to microscopic unevenness.
2. When light is incident on such rough surface, it is reflected in many directions 
3. This type of reflection is known as diffuse reflection due to this ground glass is opaque and white in color.

Image	Shadow
(1) It is formed by intersection of reflected rays.	(1) Shadow is formed when light does not reach behind the object.
(2) Image is seen when reflected rays approach to observer's eyes.	(2) No light enters the observer's eyes.
(3) Image gives more information such as colour, structure etc.	(3) Shadow does not provide such information.
(4) Image can be straight or inverted.	(4) Shadow is never inverted.

There are the following two methods to convert a glass sheet into a translucent sheet.
(i) By smearing a thin layer of oil on the glass sheet.
(ii) By covering a side of the sheet with butter paper.

$$Pinhole\,\,camera:-$$ A pinhole camera$$,$$ also known as camera obscura$$,$$ or $$dark\,\,chamber,$$ is a simple optical imaging device in the shape of a closed box or chamber$$.$$ In one of its sides is a small hole which$$,$$ via the rectilinear propagation of lighht$$,$$ creates an image of the outside space on the opposite side of the box$$.$$

All three objects will form the same kind of image of the sun irrespective of their shapes as the holes in the strips work as a pinhole camera and the strips are opaque.

A transparent glass can be changed into translucent sheet by-
i. Butter or oil could be applied which will make it partially permeable.
ii. Making the glass sheet rough by rubbing materials like sandpaper on it. It will also allow light to pass through it partially.

Position $$A$$ will form the shadow $$'a'$$.
And position $$B$$ will form the shadow $$'b'$$.
As the ball, torch and screen are in the same straight line in position $$A$$, the size of the shadow $$'a'$$ is bigger than shadow $$'b'$$, because in position $$B$$ the torch is not in coordination with ball and screen.

A medium through which light cannot pass is called the $$\text{opaque medium}.$$

Usually, the air around us is transparent that is why we can see buildings, trees, etc. But pollutions like; smoke, dust, or fogs with smoke (known as smog) absorb the light. and we can't see things around us. therefore air is not always transparent. 

Pinhole camera does not change the colour of the image and it is same as that of the object. But, image formed is inverted and left - right reversed.

Shadow is the dark space behind an opaque object where light does not reach.

At noon the sun is directly overhead. So, the sun rays fall vertically on the body. Hence the shadow is very short. In the morning and evenings, the sun rays fall in an inclined / slanting manner. So, the shadows are long. 

A medium which allows the passage of light through it easily, is called a transparent medium. 
Examples: glass, air.

The image formed in a pin-hole camera is real and inverted.

Shadows are formed when an opaque object or material is placed in the path of rays of light. The opaque material does not let the light pass through it. The light rays that go past the edges of the material make an outline for the shadow.

A shadow is formed when the path of light is obstructed by an object.

When 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 the 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 from all the other points between A and B, on passing through the pin hole strikes the tracing paper in between A' and B'. As a result, an inverted image of the candle is seen on the tracing paper fig. shows the simple ray diagram for die formation of image.

The simple applications of rectilinear propagation of light are pin hole camera, formation of shadows and eclipses. 

Rectilinear propagation of light is the property of light due to which it travels in a straight line.

A substance through which light passes is called a transparent substance. 
Examples : Glass, air, water etc.

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

1. Transparent objects - Those objects through which light can pass easily are called transparent objects, e.g. Water, glass, air. 
2. Translucent object - The object through which light can pass partially are called translucent object, e.g. tracing paper, waxed paper. 
3. Opaque object - The objects which do not allow the light to pass through are called opaque objects, e.g. wood. 

Transparent objects are those through which light can easily pass. Water and glass are examples of transparent objects.

Transparent objects are: Glass, water, air etc.

Opaque	Transparent	Translucent
an ordinary paper wooden piece steel plate  stone book milk	A glass strip kerosene oil water	greased paper tracing paper polythene sheet glycerine mustard oil grounded glass

The same shadow will be formed on screen $$A$$ and $$B$$ because formation of image depends on the size and shape of the opaque object. As the same bowl is used in both the cases so, the same shadow will be same in both cases.

The ground acts as a screen for the ball lying on ground as the lights are falling on the opaque object. But the shadow disappears with the height of the ball in air because the ground is at far distance from it.

Torch $$A$$ and $$B$$ are placed in front of the screen so they will form image. As torch $$C$$ is placed parallel to the screen, it will not form a shadow of the ball because light travels in straight line.

No, the shadows of a bird or an aeroplane can't be seen on the ground, when they are flying at higher altitude, because to obtain shadow, the object should be near the screen and as the distance is very much between will be formed.
To obtain shadow of a bird or an aeroplane, they must fly closer to the ground.

The shadow formed will be of the shape of the flower with its stalk, but, dark in colour.

The multiple shadows at a time of an object can be obtained when the light falls on the same object from different sources at a time like torch, sun, bulb, etc.)
For example - In a football match, many shadows of one player are seen at a time because of the lights falling on him from different direction.

Shadow is the dark patch formed when an object obstructs the path of the light. Hence, no light reaches in the shadow region due to which the colour of the shadow is black. So, the colour of shadow is independent of the colour of the object because light is always absent there.

i. Lighter image will be formed of muslin cloth, as it is translucent, so the light will pass partially through it.
ii. Glass is transparent so shadow formation will not take place.
iii. The sheet of plywood is an opaque object, thus, the perfect dark shadow will be obtained.

Shadow: When light fall son an opaque object, light is obstructed and a dark patch on a screen kept behind is called shadow. This is because light propagates in straight line. If distance between object and screen is less, the shadow will be (umbra) dark and smaller. 
If the distance is increased shadow will be dim and larger. Conditions Required for a shadow to form are: 
1. There should be a source of light. 
2. An opaque object. 
3. A screen. 
4. The opaque object is placed between the source of light and the screen. 

Shadow : When light falls on an opaque object, light is obstructed and a dark patch on a screen kept behind is called shadow. This is because light propagates in straight line. If distance between object and screen is less, the shad o w will be (umbra) dark and smaller.
If the distance is increased shadow will be dim and larger.