[Physics Class Notes] on Shadow Formation Pdf for Exam

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.

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

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.

Conclusion

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.