Question

Which colour of the light has the longest wavelength?
A. Red
B. Blue
C. Green
D. Violet

Answer 1

Hint:We know that the spectrum of visible light is a part of electromagnetic waves which can be easily observed by the human eyes. This visible spectrum has different colors according to their wavelengths ranging from $400nm$to $700nm$ Therefore, for solving this question, we need to know how the visible light is separated into a spectrum of colors.

Complete Step by Step Answer:
We know that the visible light separates into a spectrum of seven colors when it travels through a prism.

These seven colors from bottom to top are Violet, Indigo, Blue, Green, Yellow, Orange and Red as shown in figure and we can call them “VIBGYOR”.

Now, it is clear that as we move from bottom to top, the wavelength of light increases.
Therefore, the wavelength of red light is maximum.

Thus, the red colour of the light has the longest wavelength.

Hence, option A is the correct answer.

Additional information:
We know that frequency is inversely proportional to the wavelength of the light and it increases from top to bottom as shown in figure. Therefore, being at the top, the red light has maximum wavelength and minimum frequency.

Note: Here, we have seen the wavelength and frequency of the red light which is at the top. Similarly, it can be concluded for the violet light that it has the minimum wavelength and maximum frequency as it is at the bottom position in the spectrum of visible light.