Why do shadows move in a curved path

Similarly, the sun can also cause this effect. Right before sunset, the sun's light is squashed into a flattened disc by atmospheric refraction. The light from the sun near sunset therefore acts like it came from a light source that is more extended in the horizontal direction than in the vertical direction. Looking closely at the shadow of your hand near sunset, you can see that it is more blurry in the horizontal direction than the vertical, proving that the blurry nature of everyday shadows is caused by the sun being an extended source.

Diffraction can also cause shadows to be blurry, but the effect is more rare in everyday life stated more carefully: diffraction itself is common in everyday life, but diffraction causing the blurriness of shadow edges is less common.

Diffraction is a wave effect where waves are able to bend around the corners of obstructions. First of all, diffraction is a weak effect that depends on the wavelengt of light. The wavelength of visible light is on the order of hundreds of nanometers. As a result, simple edge diffraction, such as would make shadow edges blurry, happens on a very small scale. Diffraction effects can be amplified if very small structures are used, such as diffraction gratings or fog droplets.

But at that point, you are not really producing shadows anymore, but are producing complex diffraction patterns. As far as shadows go, the diffraction effects of everyday objects on visible light are largely too weak to notice. Secondly, diffraction is a coherent effect that typically requires a nearly monochromatic beam such as a laser beam in order to become significant.

The pinhole camera works on the principle that light travels in a straight line. Light rays coming from an object and going in through the pinhole, travel in straight line to the screen. If we look into the pinhole camera by keeping our eye at its back side, we will see an image of the tree on the screen. This is because some of the light coming from the tree passes through the pinhole to form an image on the screen. The light coming from tree passes through the pinhole of the pinhole camera in a straight line.

The working of pinhole camera illustrates the property that light travels in straight line. Due to the crossing over of light rays at the pinhole, the top of the tree comes at the bottom in image and the bottom of the tree comes at the top in image. The upside down image of an object formed by a pinhole camera is called an inverted image. An inverted image is formed in a pinhole camera because the light rays coming from the top and bottom of the object cross over at the pinhole.

Main characteristics of the image in a pinhole camera. The pinhole cameras were used for taking photographs. The pinhole cameras is kept small so that only a very small number of light rays pass through it and a sharp image of the object is formed on the screen. If the pinhole camera is made bigger, then a large number of light rays from a given point of the object pass through it due to which a blurred image of the object is formed.

Natural pinhole. On a sunny day, when we pass under a tree covered with a very large number of leaves, we often see bright circular patches of light on the ground. These bright circular patches of light are the pinhole images of the sun. This is because the small holes between the cluster of the leaves act as a pinhole and light coming from the sun passes through these natural pinholes to form bright circular images of the sun on the ground below the shady tree.

In this case, the sun is the objects, the tiny gaps between leaves are the pin holes and the ground at as the screen. When an object is placed in front of a source of light, it produces a shade or dark area behind it. Shadows are formed when light is stopped by an object. An opaque objects stops the light completely, so an opaque object casts a dark shadow behind it. A translucent objects stops the light partially, so a translucent object casts a weak shadow.

A transparent object does not stop any light from passing through it so a transparent object does not cause any shadow behind it. A shadow is formed when an opaque object comes in the path of light and stops it. An object forms shadow on the opposite side to the source of light. The shadows of objects are usually similar in outline to the object and hence we can identify the object from their shadows. The shadow of a ceiling fan hung in the centre of room will fall on the side opposite to the lighted electric bulb.

A lighted candle fixed in a room will also cast our shadow and that of the ceiling fan on the opposite side. The sunlight also forms shadows of the objects which are on the ground or near the ground. If we stand in the sun, our body cast a shadow on the ground.

And when we walk in the sun, our shadows always walk with us. Our shadow is very long in the morning when the sun just rises. The length of our shadow goes on decreasing till noon. Our shadow is shortest at noon. The length of our Shadow starts increasing in the afternoon.

And our shadow becomes very long in the evening, just before sunset. The shadow of an object can be seen only on a screen. The surface such as the walls of a room, a building and even ground act as screen for the shadows which we see in our everyday life.

We require 3 things to observe a shadow. Shadows are formed because light rays travels in a straight line, and they cannot bend round the corners of the objects.

The shape of the shadow is also the same as the shape of the object because light travels in a straight line path. When a bird is on the ground, we can see its shadow which is formed by sunlight. The bird obstructs the sunlight to form shadow on the nearby ground.

When the same bird is flying high up in the air, even then the bird obstructs the sunlight falling on it but its shadow is not seen on the ground because the ground is very, very far below the bird.

When an aeroplane is parked on the ground, we can see it shadow which is formed by sunlight. The aeroplane obstructs the sunlight to form a shadow on the nearby ground.

When the same aeroplane is flying high up in the air, even then the aeroplane obstructs the sunlight falling on it but its shadow is not seen on the ground because the ground is very, very far below the aeroplane. Sometimes the shadow of opaque objects are not seen clearly. Spread a sheet of paper on the ground. Hold a familiar opaque object at some height, so that its shadow is formed on the sheet of paper on the ground.

Ask one of your friends to draw. Draw outlines of the shadows of other objects in a similar way. Now, ask some other friends to identify the objects from these outlines of shadows. How many objects are they able to identify correctly? Do you observe your shadow in a dark room or at night when there is no light?

Do you observe a shadow when there is just a source of light and nothing else, in a room? It seems we need a source of light and an opaque object, to see a shadow. Is there anything else required?

This is an activity that you will have to do in the dark. In the evening, go out in an open ground with a few friends. Take a torch and a large sheet of cardboard with you. Hold the torch close to the ground and shine it upwards so that its light falls on your friend's face.

You now have a source of light that is falling on an opaque object. If there were no trees, building or any other object behind your friend, would you see the shadow of your friend's head?

This does not mean. After all, the light from the torch is not able to pass through his body to the other side. Now, ask another friend to hold the cardboard sheet behind your friend. Is the shadow now seen on the cardboard sheet? Thus, the shadow can be seen only on a screen.

The ground, walls of a room,. Shadows give us some information about shapes of objects. Sometimes, shadows can also mislead us about the shape of the object. In Fig. Have fun! Place a chair in the school ground on a sunny day. What do you observe from the shadow of the chair? Does the shadow give an accurate picture of the shape of the chair? If the chair is turned around a little, how does the shape of the shadow change?

Take a thin notebook and look at its shadow. Then, take a rectangular box and look at its shadow. Do the two shadows seem to have a similar shape? Luminous objects d based upon the principle of rectilinear propagation of light. Glow-worm is a e illuminating objects. Beginnings Endings 1. A pinhole camera is d based upon the principle of rectilinear propagation of light.

Moon and Venus are e illuminating objects. Rectilinear propagation of light is a travelling of light in a straight line. Luminous objects c give out light of their own. Glow-worm is a b natural source of light. Write True T or False F against the following statements in the given brackets: 1. Stars are luminous bodies. Translucent objects do not form shadows. An oiled paper is an example of an opaque body. A pinhole camera can take pictures of moving objects. A polished metal surface can't act as a mirror.

We can see shadow even if there is no light. A heated iron rod becomes luminous but on cooling it becomes non-luminous. Image of an object is always black, shadow shows the colour of the object. True 2. False Translucent object form a light shadow. False An oiled paper is an example of translucent body. True 5. False A Polished metal surface can act as a mirror. False We see shadow of an object in the presence of light. True 8. False Shadow of an object is always black.

Image shows the colour of the object. The phenomenon of travelling of light in straight lines is called rectilinear propagation of light.

Opaque medium is a medium that does not allow light to pass through it. For example, wood and metals are opaque mediums. Non-luminous bodies do not emit light of their own. Examples: Sun and stars Examples: Wood and chair. No, images are not same as shadows. Images are formed when light is reflected from a mirror or any shinning object and carry all the details of the object such as colour, size, etc. However, shadow of an object is always black and it does not carry the details of the object like colour, size, etc.

A pinhole camera is based on the principle of rectilinear propagation of light. According to this principle, light always travels in a straight line. Any smooth, polished surface that can reflect light rays in the same medium is called mirror. Example: Looking glass, rear view mirror of vehicles, barber's mirror, etc.

Transparent bodies Translucent bodies Transparent bodies allow light to pass through them completely. Translucent bodies allow light to pass through them partially. Examples: Air, glass, water, etc. Examples: Frosted glass, greased paper, wax paper, etc. Opaque bodies are those bodies that do not allow light to pass through them at all.