In simple terms, anything that makes things visible is light. But that isn’t a proper scientific definition. In scientific terms, light is a form of energy with both wave and particle nature that creates sensation of vision. At this point, you are not required to check the wave and particle nature, and hence we will focus on the syllabus covered in the NCERT book.

Light has some unique properties that make it different from other sources of energy. The light has the following properties.

• Light always travels in a straight line, popularly termed as the rectilinear propagation of light.
• The speed of light in a vacuum is 3 x 10^8 m/s. It only takes approximately 8 minutes for light to reach the earth from the sun.
• Light has two unique phenomena: reflection and refraction, as discussed in the coming section.

Since we know that light travels in a straight line if any object comes in between the light’s path, we can see three different types of phenomenon. These phenomena are categorised into three types that are discussed below.

Opaque: When the light strikes an object and cannot pass through it, it makes a shadow of the object on the other side of the light source. These objects are called opaque objects as they do not allow the light to pass through the object—for example, the wooden door, the wall, metal sheets and more.

Transparent: If you can see through any object, they are the transparent object. For example, the air, water and clear glass are objects through which you can see the other side.

Translucent: These objects occupy the properties between the opaque and transparent object as they allow the lights to pass but not all. Hence, if you look through the translucent object, you will see a blurred image of the other side as the light cannot completely pass through these objects. For example, butter paper, frosted glass, tissue and more.

When we talk of light and shadows, as they complement each other, we look at the optical physics section of science. Shadows are 2-D dark images formed when the light cannot pass through an object. As we know, light travels in a straight line, and hence whenever opaque objects come in between the path, it casts natural shadows of the objects on the other side of the light. 

The lights get entirely blocked by the object, and hence the other side forms a dark image of the space that blocks the light.

Reflection of light is an important optical phenomenon that forms the core of ray optics. When you use a mirror and place it in the light beam’s path, you can see that the light gets reflected in the opposite direction. Hence, instead of going in the direction of the incident beam, the light changes its direction. You can also make a pinhole camera with this phenomenon. Two main laws of reflection are given below.

•         The incident ray, the reflected ray, and the normal should be on the same platform.
•         The angle of incidence is equal to the angle of reflection.

Similarly, we have another optical phenomenon called refraction. The speed of the light changes when it passes through different mediums. The refraction phenomenon is responsible for the formation of the rainbow in the sky.

Light is an important exam topic that covers the optics and natural shadows concepts. There are many applications of light such as bulbs, TVs, rainbow formation, mirrors and more. Reflection and refraction are some of the most common phenomena associated with light. You can learn more about light in the above article and prepare for your exams.

1. How many shadows are cast in the eclipse period?
   Two shadows are cast, called umbra and penumbra, during the eclipse, which gets smaller as it goes away from the sun.
2. What are the applications of rectilinear propagation of light?
   The major application can be a pinhole camera formation. Moreover, the reflection phenomenon also obeys rectilinear propagation.
3. What is the application of refraction?
   Refraction helps in the formation of the rainbow, delayed sunset and sunrise, prism experiment and more.
4. What are ‘normal’ laws of reflection?
   Normal is the perpendicular line drawn to the surface where the incident ray strikes on that surface.
5. How to make a pinhole camera?
   You need to take a card stock and cut a square hole in the middle of the card. Now take a piece of aluminium foil and tape the hole. Afterwards, you need to poke a hole in the foil and then try out the camera with candlelight.