When we are walking on the road at midday, we can observe our image on either of the four sides. This we call a shadow. Even though we all are very familiar with the shadow, we don't know what a shadow is, how is it formed? Isn't it? So we start learning about a shadow, how it forms, its sources, etc.
What is a Shadow?
A dark space or a region where an opaque object blocks the light rays is known as a shadow. The type of shadow formed depends upon the position and intensity of the source of the light. For example, in the early mornings and late afternoons, the shadows formed are elongated. But the shadow formed at noon is short and dark in nature when the sun is right above your head.
The nature of light sources can either be pointed or non-pointed (or extended). When the source of the light is a point source then there is a formation of a simple shadow known as umbra while if the source of the light is an extended light source then the shadow gets divided into the umbra, penumbra, and antumbra. These types of shadows can also be used to define the levels of darkness.
When is a Shadow formed?
Whenever the light or sun rays are blocked by any object, a black area or region is formed in a particular shape based on the object or body behind it. This is the time when the shadow is formed.
How is a Shadow formed?
To explain what a shadow is? It is essential to learn and understand transparent objects and opaque substances. Because the shadow is a place or a region where the opaque substance may restrict the light not to enter by its race, the properties of that particular region where a type of shadow is formed is called the shadow.
It is easy to understand the shadow formation and know that type of shadow because the shadow can be formed by the Sun or by the light.
Shadow- Formation by Sun
Sun is a source of shadow to form. A shadow is formed when the sun's rays are traveling in your straight line towards the earth.
The rays of the sun radiate outwards and these light rays travel nearly 300,000 km/sec in a straight line towards the earth. These light rays take only 8 minutes to reach us. It directly touches the path on the ground. If the path is a transparent object, there will not be the formation of shadow. On the other hand, if it touches the opaque substance as a part, it avoids the race entering its region and results in shadow formation.
Whatever comes in the path of these rays, they hit that object. When the object that is hit by these rays is opaque, the object blocks the light and does not let these rays pass through, which leads to the formation of shadow. When the light cannot get through an object a shadow is formed on the other side of that object. Even though the shadow is the same as the object, it is not a reflection.
Shadow- Formation by Light
Now, let us discuss light and the formation of shadows.
Along with the sun, there are many more sources of light which include light-bulbs, candle flames, computer screens, and glow-worms. Light can be observed in many forms like candlelight, sunlight, lamplight, electric light, computer light, etc. Each form of the source can create a shadow in the different scenarios. Based on the size of the light, the sharpness of shadow is observed. Shadows are formed because the movement of particles travels in light. Similar to the sunlight, the particles travel and choose a destination. If the destination is an opaque substance, it creates a blurred image based on the object's size. If we use a mobile phone to spotlight, it gives a very small shadow. This might be helpful to explain how shadows are formed.
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Just like the sun, the light from these sources also travels in a straight line but travels a shorter distance. When the contrast between the shadow and the lit surface is high, the shadows formed are more definite which is the reason why the shadows formed on a white surface can be seen more easily. The sharpness and blurriness of the shadow depend on the size of the light source. Small lights form distinct shadows while bigger lights form less distinct shadows as compared to the small lights. The shapes and sizes of shadows are dependent on the position of the light.
Size and Shape of a Shadow
While discussing shadow formation in physics, we understood how the shadow is formed. But it is also good to know about the size and shape of a shadow. It is entirely based on the size of the source object and the shape of the receiving object.
When a shadow is formed, we can observe the shape of The Shadow by the reflecting object. If it is a ball, the shadow will be circular. If it is a book, then the shadow will be either square or rectangular in shape. If it is a person, then the shape of the shadow will be a human being. Similarly, the sharpness of the shadow formed can be determined by the size of the source object. If the light rays reach the path in a big size like sunlight or tube light, the shadow has more sharpness. If the size of the source is tiny like cell phone light, Aura torchlight, etc., the shadow will appear blurred.
Seasons are also factors that determine the size and shape of the shadow. When the shadow is formed, if it is summer, the days are bright and sunny. Then the sharpness of the shadow will be high, and it stays for a longer time. If shadows are formed in the rainy season, the light cannot travel through water, and we can't observe sharp shadows. It can appear in a blur.
Here we understood what a shadow is and how it is formed. It is clear to us that when the shadow is formed how the shadow's size and shape may change from time to time, season to season, object to object. After understanding the reasons, it is clear and able to explain how the shadows are formed and the sources approximately based on a shadow's size and appearance.
FAQs on Shadow Formation
1. What is the reason behind the changes in shadow with the seasons?
The length of the shadows is affected by the tilt of the earth’s axis. When the northern hemisphere of the Earth is tilted towards the sun, and the sun is more directly overhead, during the summer, the midday shadows are very short, while during winter, the midday shadows formed are longer since the northern hemisphere is tilted away from the sun of the Earth. This is because of the lower angle of the sun during winters.
2. What is the effect of the spinning of the earth on light?
When our location on Earth is spinning towards the light of the Sun, we observe that the Sun is higher in the sky while as our location on the earth spins away, we see the sunset which is comparatively closer. When there is nothing in the path of sun rays to block the light we continue to see shadows, while when the sun rays are blocked by the magnitude of our planet and we have a night on our planet. As the earth spins again towards the sunlight, we observe the sunrise.
3. What is meant by the umbra, penumbra, and antumbra?
The umbra, penumbra, and antumbra are three different parts of a shadow. When there is a complete blockage of light by the occluding body which is the innermost and the darkest part, is known as the umbra. Then the region where only some light is obscured is known as the penumbra. Lastly, the region where the appearance of the occluding body is within the disc of the light source. Examples of umbra, penumbra, and antumbra are total eclipse, partial eclipse, and annular eclipse respectively.
4. What are some of the differences between a shadow and an image?
Some of the differences between a shadow and an image are listed below-
When the light is obstructed, a shadow is formed while the true reflection of any object refers to its image.
The region where there is the absence of light is known as the shadow while light rays tend to form images.
Only a rough outline of an object is provided by the shadow as it is only a dark patch that is formed on the surface while the image is the exact description of the object.
The formation of shadows is only on surfaces while the image cannot be seen on a screen which is formed by a plane mirror.
The size of shadows can change as the position, size of the source of light are changed while the size of images formed on a plane mirror is always the same.
5. What are some of the properties light possesses?
The most important properties that light possess are listed below-
It always travels in a straight line.
Light travels at a speed that is way more than sound which equals 3 x 10⁸ m/s.
A light can be reflected, refracted, diffracted, dispersed, polarised, and interfered with.
Light causes the phenomenon of vision.
To learn more about light and its properties students can visit Vedantu.
6. What is the Significance of Shadows?
Shadows are significant in physics and the arts. Even though they didn't recognize, some of the benefits caused by the shadows are:
It helps to identify that the light travels in a straight line.
People started learning and remembering the shapes of objects based on their shadows.
Shadows can help the photographers to maintain and direct attention to a specific point.
It acts as a focal point because it is specified the point where we need to focus on.
Shadows help in revealing the texture of the structure of the object.
Several exemptions can be drawn by observing the Shadow.
Thus the shadows are helpful in various aspects.
7. What are the Types of Shadows?
Shadow is a place or a region where the source light gets restricted by the opaque substance not to enter. This region is nothing but a shadow. Its size, sharpness, and shape may vary by various factors. We have two different types of shadows based on the light source. They are:
Point Light Source:- If the lower light source is pointed to a single area and casts on a shuttle, then the shadow is known as the umbra.
Nonpoint Light Source:- If the light source doesn't have a specific point and is extended to spread, based on the size of the light source, we can define and observe the brightness of shadows. These can be determined in three ways. They are: