In the visible spectrum of light, which colour has the highest frequency (and therefore the shortest wavelength)?

Introduction / Context:
White light from the Sun or a lamp can be dispersed into its constituent colours, forming a spectrum from red to violet. Each colour corresponds to light of a particular wavelength and frequency. This question asks which colour in the visible spectrum has the highest frequency and, correspondingly, the shortest wavelength.

Given Data / Assumptions:

• We are considering only visible light, which ranges approximately from red to violet.
• The visible spectrum is often remembered using the sequence VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).
• The speed of light in vacuum is constant for all colours, so frequency and wavelength are inversely related.
• Frequency increases as we move from red to violet in the visible range.

Concept / Approach:
For electromagnetic waves, the relationship between speed (c), frequency (f) and wavelength (λ) is c = f * λ. Since the speed of light c is constant in vacuum, a higher frequency corresponds to a shorter wavelength. In the visible spectrum, red light has the longest wavelength and the lowest frequency, while violet light has the shortest wavelength and the highest frequency. Therefore, among the listed colours, violet has the highest frequency.

Step-by-Step Solution:
Step 1: Recall the order of colours in the visible spectrum from low frequency to high frequency: Red, Orange, Yellow, Green, Blue, Indigo, Violet. Step 2: Recognise that as we move from red to violet, wavelength decreases and frequency increases. Step 3: Among the given options (Violet, Red, Indigo, Green), red is at the low-frequency end and violet is at the high-frequency end. Step 4: Although indigo and blue are closer to violet than green and red, violet still has a higher frequency than indigo. Step 5: Conclude that violet has the highest frequency in the visible spectrum.

Verification / Alternative check:
Approximate wavelength ranges support this: red light is around 620–750 nm, green around 495–570 nm, blue and indigo around 450–495 nm, and violet around 380–450 nm. Since frequency f = c / λ, shorter wavelengths (violet) correspond to higher frequencies. Textbooks consistently state that red has the longest wavelength and lowest frequency, while violet has the shortest wavelength and highest frequency within the visible range.

Why Other Options Are Wrong:
Red: Red has the lowest frequency and longest wavelength among visible colours, the opposite of what is asked.

Indigo: Indigo has a relatively high frequency but still slightly less than violet in the usual ordering.
Green: Green is in the middle of the spectrum, with frequency higher than red and yellow but lower than blue, indigo and violet.

Common Pitfalls:
Some learners confuse energy, frequency and wavelength, or misremember the order of colours. A helpful memory aid is that as you go from red to violet, energy and frequency increase while wavelength decreases. Another mnemonic is the reverse of VIBGYOR (ROYGBIV), which reminds you that red is at one end and violet at the other.

Final Answer:
In the visible spectrum, Violet has the highest frequency.