Among the following colours of visible light, which has the highest photon energy and therefore the highest frequency?

Introduction / Context:
Visible light is made up of a spectrum of colours, often remembered by the sequence red, orange, yellow, green, blue, indigo and violet. Each colour corresponds to light waves of different wavelengths and frequencies. Photon energy is directly proportional to the frequency of light and inversely proportional to its wavelength. This question asks which listed colour among violet, red, blue and white corresponds to the highest photon energy.

Given Data / Assumptions:
- The visible spectrum runs from red at the long wavelength end to violet at the short wavelength end.
- Photon energy E is related to frequency f by E = h * f, where h is Planck constant.
- Frequency and wavelength are related by c = f * λ, with c being the speed of light and λ the wavelength.
- White light is a mixture of many colours, not a single wavelength.

Concept / Approach:
Since E = h * f, higher frequency means higher photon energy. Because c = f * λ, for a constant speed of light in vacuum, shorter wavelength corresponds to higher frequency. Within the visible range, red light has the longest wavelength and lowest frequency, while violet light has the shortest wavelength and highest frequency. Blue light lies between green and violet, so its frequency and energy are higher than red but lower than violet. White light is not a single frequency; it is a combination of many wavelengths and thus does not correspond to a single photon energy. Therefore, among the options, violet light has the highest photon energy.

Step-by-Step Solution:
Step 1: Recall the order of colours in the visible spectrum: red, orange, yellow, green, blue, indigo, violet. Step 2: Recognise that as you move from red to violet, wavelength decreases and frequency increases. Step 3: Use E = h * f to conclude that higher frequency light has higher photon energy. Step 4: Compare red and blue. Blue has a shorter wavelength and higher frequency than red, so its photons have more energy. Step 5: Compare blue and violet. Violet has an even shorter wavelength and higher frequency than blue, so its photons carry more energy. Step 6: Note that white light is a mixture of colours and does not correspond to a single energy; it is not a separate spectral colour.

Verification / Alternative check:
Approximate wavelength ranges confirm this ordering. Red light is around 620 to 750 nanometres, green around 495 to 570 nanometres, blue around 450 to 495 nanometres and violet around 380 to 450 nanometres. Since violet has the smallest wavelength among these, it has the highest frequency and thus the highest photon energy. Spectral diagrams and physics texts consistently place violet at the high energy end of the visible band.

Why Other Options Are Wrong:
Red: Red has the longest wavelength and lowest frequency among common visible colours, so its photons have lower energy compared with blue and violet.
Blue: Blue photons are more energetic than red photons but less energetic than violet photons because blue wavelengths are longer than violet wavelengths.
White: White is not a single spectral colour; it is a combination of many wavelengths, so it does not represent a single photon energy.

Common Pitfalls:
A common mistake is to think that white is the highest energy colour because it appears brightest. However, brightness is related to intensity and perception, not directly to the energy per photon of a specific wavelength. Another confusion is mixing up wavelength and frequency trends, forgetting that shorter wavelength means higher frequency and higher photon energy. Memorising the red to violet order and remembering that violet is the high energy end of visible light helps avoid these errors.

Final Answer:
Among the listed colours, violet light has the highest photon energy and the highest frequency.