Shadow Formation

In this article, we will discuss about shadow formation, umbra and penumbra, characteristics of shadows.

What is shadow?

Have you ever made the shadows of different animals like dogs, camels or butterflies with your hands on the wall of your room?

Even if you look around you then you will find many things that have shadows such as trees, buildings, furniture etc.

We can define shadow as “A shadow is a dark region behind an opaque object where light is blocked by the object”

Shadow Formation

Three basic things are required in shadow formation:

  • Source of light
  • Opaque object
  • Screen or surface behind the object

We have already learned that the light travels in straight lines. A shadow is formed when light hits an opaque object which stops the rays of light from passing through it. When the object blocks the light’s path, then a dark region appears on the other side. This dark region is called a shadow.

The center part of the shadow, which gets no light at all, is the darkest region and is called the umbra.

The partial dark region of a shadow around the umbra that gets light from some parts of the source of light is called the penumbra.

shadow_formation

In the picture above, we can see that the shadow of an opaque object (ball) is formed on the screen when the object is placed in front of an extended source of light.

Note: Umbra and penumbra are formed only when an opaque object is placed in front of an extended source of light.

The size of the umbra and penumbra depends on various factors such as the size of the source, size of the object, and the distance between the source and the object as well as the distance between the object and the screen.

shadow_formation

Characteristics of shadows

  • Only opaque objects can form shadows.
  • Shadows will always be formed on the opposite side of the light source.
  • Shadow is always black in color.
  • It needs a screen for being formed.
  • The shadow of an object is erect i.e same side up as the object.
  • The size of the shadow depends upon the size of the object, the distance between light source and object and the distance between object and the screen.
  • It is always either large or the same size as that of the object.

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