Light is a fascinating phenomenon that has properties of both waves and particles. The color of light that we perceive depends on its wavelength, which is related to its frequency. Though it may seem counterintuitive, the color with the highest frequency actually has the longest wavelength.
The Electromagnetic Spectrum
Visible light that we can see with our eyes is just a small part of the entire electromagnetic spectrum. This spectrum includes radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays, in order of increasing frequency and decreasing wavelength. The full electromagnetic spectrum is pictured below:
| Type of Radiation | Wavelength Range | Frequency Range |
|---|---|---|
| Radio waves | 1000 km – 1 mm | 3 Hz – 300 GHz |
| Microwaves | 1 mm – 1 mm | 300 GHz – 300 MHz |
| Infrared | 1000 μm – 700 nm | 430 THz – 300 GHz |
| Visible light | 700 nm – 400 nm | 430 THz – 750 THz |
| Ultraviolet | 400 nm – 10 nm | 750 THz – 30 PHz |
| X-rays | 10 nm – 0.01 nm | 30 PHz – 30 EHz |
| Gamma rays | 0.01 nm – 0.001 pm | 30 EHz – 3 EHz |
As this table shows, radio waves have the longest wavelengths and lowest frequencies, while gamma rays have the shortest wavelengths and highest frequencies. Visible light lies somewhere in the middle, with wavelengths from about 400-700 nanometers (nm).
The Visible Spectrum
The visible spectrum is the narrow slice of electromagnetic radiation that our eyes can detect. The colors we see, from longest to shortest wavelength, are red, orange, yellow, green, blue, indigo, and violet. This order of colors produces the familiar rainbow pattern.
Here are the approximate wavelengths for each color in the visible spectrum:
| Color | Wavelength (nm) |
|---|---|
| Red | 700-635 |
| Orange | 635-590 |
| Yellow | 590-565 |
| Green | 565-495 |
| Blue | 495-450 |
| Indigo | 450-420 |
| Violet | 420-400 |
As this table demonstrates, red light has the longest visible wavelength at 700 nm, while violet light has the shortest visible wavelength at about 400 nm.
Relationship Between Wavelength and Frequency
Wavelength and frequency are intrinsically linked for all electromagnetic radiation by this equation:
Frequency x Wavelength = Speed of light
Or, f x λ = c where f is frequency, λ is wavelength, and c is the speed of light (3 x 108 m/s).
This means that as wavelength increases, frequency decreases, and vice versa. The lowest frequency visible light (red) has the longest wavelength, while the highest frequency visible light (violet) has the shortest wavelength.
Why Violet Light has the Highest Frequency
Based on the properties of the electromagnetic spectrum and the visible light spectrum, violet light has the highest frequency of visible colors. This is because:
- Violet has the shortest wavelength of visible light colors, at about 400-420 nm.
- According to the equation relating wavelength and frequency, shorter wavelengths correlate to higher frequencies.
- Therefore, violet has the highest frequency since it has the shortest wavelength of the visible spectrum.
Numerically, violet light has a frequency around 750 THz (750 x 1012 Hz), while red light has a frequency around 430 THz.
Why Red Light has the Longest Wavelength
Conversely, red light has the longest wavelength of the visible spectrum. Here’s why:
- Red has the longest wavelength range at 700-635 nm.
- Longer wavelengths equate to lower frequencies based on the wavelength-frequency equation.
- Thus, the longest visible wavelength of ~700 nm corresponds to red light.
This also logically follows the pattern of the visible spectrum, with wavelengths decreasing from red to violet as frequency increases.
Real World Examples
We can observe the relationship between color, wavelength, and frequency in the real world:
- Rainbows – Rainbows display the visible spectrum from red to violet, showing the progression of decreasing wavelength and increasing frequency.
- Sunsets – More blue light is scattered away at sunset, leaving mostly longer wavelength red hues.
- Fluorescence – Materials absorb higher frequencies then emit lower frequencies, like how a fluorescence light bulb emitting green is powered by UV light.
Conclusion
In summary, violet light has the highest frequency visible color despite having the shortest wavelength. This inverse relationship arises from the equation relating wavelength and frequency. While not intuitive, it has to do with violet light waves oscillating incredibly fast – trillions of times per second – as they propagate. Understanding the counterintuitive connection between color, frequency and wavelength provides insight into the underlying physics of light and electromagnetic radiation that makes up our universe.
