When you turn on a torch (flashlight) in a dark room, the light emitted from the torch travels in straight lines until it encounters an object or surface. This phenomenon is known as light propagation.
When the light reaches an object or surface, it can interact with it in different ways. The three primary interactions are absorption, reflection, and transmission. Let's explore each of them:
Absorption: Some objects absorb light energy, converting it into other forms of energy, such as heat. When light encounters an object that absorbs the specific wavelengths of the torch's light, the energy is transferred to the object. Consequently, the object appears darker because it does not reflect or transmit the light to our eyes. So, if the light from the torch is absorbed by objects in the room, we won't see it beyond those objects.
Reflection: Reflection occurs when light bounces off an object's surface. If the surface is smooth and reflective, like a mirror, the light will reflect off it and change direction. This redirected light can reach our eyes, allowing us to see the object. However, if the surface is rough or non-reflective, the light scatters in different directions, making it harder to see the object or surface clearly.
Transmission: Transmission occurs when light passes through certain materials, such as transparent or translucent objects. If the objects in the room are transparent or translucent, the light can pass through them and continue propagating. In this case, we might still see the light if it travels through these objects or surfaces.
In a dark room, if there are no objects or surfaces to interact with the light, it continues to propagate until it disperses over a large area or eventually becomes too weak to be detected by our eyes. This is why we can see the light from a torch only until it encounters an object, gets absorbed, reflected, or transmitted, and no longer reaches our eyes.