What colour has the lowest frequency in the spectrum of white light?

Analysis

The question asks for the color with the lowest frequency within the visible spectrum of white light. To solve this, we must understand the relationship between frequency, wavelength, and the dispersion of light.

Concept Explanation

When white light is dispersed (split) into its component colors, it forms the spectrum known by the acronym ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet).

In physics, the wave equation is given by:

Where:

• $v$ = speed of light (constant in a vacuum)
• $f$ = frequency
• $\lambda$ (lambda) = wavelength

Because the speed of light ($v$) is constant, frequency ($f$) and wavelength ($\lambda$) are inversely proportional. This means that the color with the longest wavelength will have the lowest frequency.

In the visible spectrum:

• Red light has the longest wavelength (approximately 700 nm).
• Violet light has the shortest wavelength (approximately 400 nm).

Since Red has the longest wavelength, it must have the lowest frequency.

Step-by-Step Solution

1. Recall the spectrum order: The colors are arranged by increasing frequency (or decreasing wavelength) as follows: Red $\rightarrow$ Orange $\rightarrow$ Yellow $\rightarrow$ Green $\rightarrow$ Blue $\rightarrow$ Indigo $\rightarrow$ Violet.
2. Identify the extremes: Red is at one end (lowest frequency, longest wavelength) and Violet is at the other end (highest frequency, shortest wavelength).
3. Compare the options: • Red: Lowest frequency • Yellow: Higher frequency than Red • Blue: Higher frequency than Red and Yellow • Indigo: Higher frequency than Red, Yellow, and Blue
4. Conclusion: Red is the color with the lowest frequency.

Exam Tip

Remember the mnemonic ROYGBIV. Just keep in mind that Red is like a "lazy" wave—it is long and slow (low frequency), while Violet is a "busy" wave—it is short and fast (high frequency). This will help you remember the relationship between frequency and color every time!