Which colour has the longest wavelength ?

Question

Accepted Answer

Option 1, Red, is the correct answer because red light has the longest wavelength in the visible spectrum. The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye, and it ranges from approximately 380 nanometers (nm) to about 750 nm. Within this range, red light has wavelengths ranging from about 620 nm to 750 nm, making it the longest among the visible colors.

1. **Explanation for Option 1 (Red):**
   - Red light's longer wavelength means it is less scattered by atmospheric particles, which is why the sky appears red during sunrise and sunset when the light path through the atmosphere is longest. This characteristic of having the longest wavelength is why red is used in various applications, such as stop signs and traffic signals, because it can be seen from a greater distance.

2. **Explanation for why other options are incorrect:**
   - **Option 2 (Pink):** Pink is not a spectral color but rather a combination of red and white light. It does not have a specific wavelength in the visible spectrum, so it cannot have the longest wavelength.
   - **Option 3 (Blue):** Blue light has a much shorter wavelength, typically ranging from about 450 nm to 495 nm. This shorter wavelength causes blue light to scatter more than red light, which is why the sky appears blue during the day.
   - **Option 4 (Green):** Green light has wavelengths ranging from about 495 nm to 570 nm. While longer than blue, green wavelengths are still shorter than red wavelengths, making green an incorrect choice for the longest wavelength.

In conclusion, red light's position at the end of the visible spectrum with the longest wavelength makes Option 1 the correct answer.