Question

Why is red used to stop the vehicle?

Answer 1

Hint: Here the concept of VIBGYOR will play an important role. Especially its role with wavelength. That is, the relation of colours with wavelength is the foundation of the solution to this question.

Complete answer:
We can easily answer this question after knowing the pattern of wavelengths along VIBGYOR ( violet indigo blue green yellow orange red). Prior to that, it must be known that the scattering of the light is the least if the wavelength of the light is the longest. This means that the scattering of light is inversely proportional to the wavelength of the light.

When we move along VIBGYOR, the wavelength of the colours increases. This means that red has the highest wavelength of all and it will scatter the least. As it scatters the least, the colour red must be visible from far away and people can notice it beforehand.

So in case of any serious problem or danger, it is very much important to let the people know that something is wrong ahead. In the case of the traffic signal, red colour is used to stop the vehicle because people can notice it from far away and hence they will understand that we need to slow down and follow the rules.

Note: The colour blue is known to have the least wavelength and so it scatters the most. This is the primary reason the colour of our sky appears blue when the sunlight refracts from the surface of our planet even though it is actually black.