Ans: Light is just a form of energy (also called electromagnetic energy) that travels at a constant speed from one place to another and gets reflected, refracted or absorbed by the surfaces of objects. Light isn’t made of matter, so it doesn’t have mass. When it hits our eye, we see the objects from which the light is reflected or emitted.
So, do we really see light? The simple answer is NO!
We only see the effect of light that occurs in our eyes. The light-sensitive cells of our eyes undergo chemical reaction when exposed to light. Electrical signals (produced by these reactions) are transferred to the brain by the optic nerve.
Moreover, light is only the small portion (detectable by our eyes) of the large electromagnetic spectrum. The other significant portions of electromagnetic radiation that we are familiar with are radio waves, infrared, ultraviolet, and X-rays etc. But the human eye cannot detect these radiations. Our eyes can only sense light, also called visible light.
How Fast Light Travel?
Every radiation of electromagnetic spectrum including visible light travel at constant speed of 299,792,458 m/s or 186,000 miles/second. It only takes 1.3 seconds for the light to reach from the moon to earth, and 8 minutes to reach from the sun.
Light possesses the fastest known speed in our universe, and no object with mass can reach that speed. Although, material objects can reach close to the speed of light under specific circumstances.
The laws of classical physics don’t work anymore when objects reach near the speed of light. Einstein proposed the theory of relativity to resolve this and described what happens when things reach closer to the speed of light.
How Do We See Colours?
The visible light not only allows us to see objects, but it also allows us to see the object in a wide variety of colours. It is because the visible light starts from the wavelength of 700nm and ends at 400nm. The colours that we can see a change from 700nm (dark red colour) to 400nm (dark blue colour). The colours we see may be the single wavelengths of light or the mixture of several wavelengths. For example, the sunlight is the mixture of all wavelengths of light and we see it as white light. Just check the light spectrum image above and notice that there is no white colour, it just a mixture of colours.
Why Objects Have Different Colours?
As we know from the above discussion that, white light is the mixture of colours. So, when this white light falls on an object, it absorbs some colours of light and reflects the remaining colours to the surrounding. When our eyes catch that reflected light, it sees the object’s colour that it reflected.
For example, when the light hits the green box, it absorbs all the colours of light and reflects only green colour. As a result, we see it as green. Similarly, black coloured objects absorb all the colours of light so we see it as black. Furthermore, the white coloured objects don’t absorb any colour at all, so we see them as white. There are some materials which don’t absorb light or reflect them. As a result, we can see through these objects. These objects are called transparent objects, e.g., glass.