Question

What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:
(a) the electric bulb
(b) a piece of white paper.

Answer 1

Hint: The eyes of the humans absorb most of the light coming from the environment or from a luminous source. For humans to be well aware of the presence of light in their surroundings, the light waves have to get absorbed into our retina through the pupil.

Complete Step By Step Answer:
Generally, when the luminous sources of light emit their light in the environment, most of it gets absorbed by the non luminous object which is present in the environment which goes on to increase the temperature of that particular object. But some of the rays of light are reflected by the objects and these rays of light which are reflected may enter into our eyes to be seen. The light which is reflected from different parts of a particular object falls into our eyes to form an image. This is the reason that we are able to see the object. Usually, the light which gets reflected from the object passes through a lens which is present in our eyes which converges these light rays onto the retina to form an image.
We are not able to see anything in a completely dark room as there is no light present in the darkroom which can be reflected onto our eyes.
(a) After switching on an electric bulb in the dark room which acts like a light source, we are able to see it as it emits light and that light reaches our eyes.
(b) After switching on the electric bulb in the dark room which acts like a light source, we are able to see a piece of white paper because of the diffused reflection which takes place from the surface of the white paper.

Note:
It is important to note that for clarity, objects that need to be reflected to be seen are non-luminous objects. Luminous objects do not have to be reflected in order to see, as long as the light they emit can get in our eyes.