Exploring Light and Wavelengths: The Science Behind Color

Understanding Light and Wavelengths

Light permeates our surroundings, consisting of various colors, each defined by a unique property known as wavelength. The wavelength is the distance between two consecutive peaks or troughs of a wave, influencing our perception of colors as well as their natural behavior. Some colors possess shorter wavelengths, while others have longer ones. By studying wavelengths, we gain a deeper understanding of light and its effects.

Which Colour has the Longest Wavelength?

The color with the longest wavelength in the visible spectrum is red. Red light waves are characterized by their slower speed and lower energy, causing them to stretch out the most. This unique property allows red light to travel greater distances without scattering, making it highly visible in conditions such as fog, rain, or dust. This visibility is also the reason why stop signs, traffic lights, and brake lights are typically red, as it captures our attention from afar.

What is Wavelength?

Wavelength refers to the distance between two consecutive high points (peaks) or low points (troughs) of a wave. To visualize this, consider the waves in the ocean; the distance from the crest of one wave to the next mirrors the wavelength of light. In the context of light, wavelengths are minuscule and measured in nanometers (nm). Generally, shorter waves carry more energy, while longer waves carry less.

Colours and Their Wavelengths

White light can be separated into a spectrum of colors using a prism, arranged by wavelength from longest to shortest:

• Red: ~620 –750 nm
• Orange: ~590–620 nm
• Yellow: ~570–590 nm
• Green: ~495–570 nm
• Blue: ~450–495 nm
• Indigo: ~425–450 nm
• Violet: ~380–425 nm

Red is at one end of the spectrum with the longest wavelength, while violet is at the opposite end with the shortest.

Why Red has the Longest Wavelength?

Red light waves are the slowest and carry the least energy among visible colors. This characteristic allows their waves to be more elongated. Positioned next to infrared light in the electromagnetic spectrum, red light can traverse long distances without scattering. This property contributes to the use of red in stop signs, traffic lights, and brake lights, making it visible from great distances and enabling it to penetrate fog, rain, or dust more effectively than other colors.

Interesting Facts About Red

• Red is the first color to disappear underwater, appearing grey or black around 15–20 feet deep.
• Mars appears red due to iron oxide (rust) present on its surface.
• Many fast-food chains utilize red in their branding, as it can stimulate appetite.
• During a lunar eclipse, the moon may appear red, a phenomenon known as a “Blood Moon.”
• Red is often the first color that humans name, following black and white.

Frequently Asked Questions (FAQs)

Q1. What is the significance of wavelength in light?
Answer: Wavelength is crucial in determining color perception and behavior in nature. It influences how light interacts with materials, affecting visibility and energy levels.

Q2. Why is red light used in traffic signals?
Answer: Red light has the longest wavelength, making it highly visible from a distance and allowing it to penetrate fog and other obstructions effectively.

Q3. How are colors arranged in the visible spectrum?
Answer: Colors in the visible spectrum are arranged from longest to shortest wavelength: red, orange, yellow, green, blue, indigo, and violet.

Q4. What happens to red light underwater?
Answer: Red light disappears first underwater, becoming grey or black at depths of around 15-20 feet due to absorption by water.

Q5. What are some uses of red in marketing?
Answer: Red is commonly used in marketing, particularly by fast-food restaurants, as it is believed to stimulate appetite and attract attention.

UPSC Practice MCQs

Question 1: Which color has the longest wavelength in the visible spectrum?
A) Blue
B) Green
C) Red
D) Violet
Correct Answer: C

Question 2: What unit is used to measure wavelength of light?
A) Meters
B) Nanometers
C) Kilometers
D) Micrometers
Correct Answer: B

Question 3: Why is red used in traffic signals?
A) It is the brightest color
B) It has the shortest wavelength
C) It has the longest wavelength
D) It is the most popular color
Correct Answer: C

Question 4: At what depth does red light begin to disappear underwater?
A) 5-10 feet
B) 10-15 feet
C) 15-20 feet
D) 20-25 feet
Correct Answer: C