Why Blue is Hotter than Red?

Why Blue is Hotter than Red?

by E. Pasion

 

Poets say “red hot” and “cold as blue”. In arts, warm tones are associated to red, orange and yellow while cool tones are that of the opposite end of the color spectrum – blue and violet.

 

However, isn’t it contradicting to what scientists say? The hottest stars for example are the blue hypergiant ones while the coolest ones are the red stars! 

 

Which color really has the highest energy? Which one has the least?

 

To answer that boggling question, we need to review the color spectrum of the visible light!

 

 

What is light?

 

White light is the combination of all colors in the electromagnetic spectrum. Light is the presence of all colors while black is the absence of all of it! As you have learned in Grade 7, light is a part of the electromagnetic wave or the EM wave! The EM wave is composed of seven different components. These components (in increasing energy) are radio wave, microwave, infrared, visible light, ultraviolet, x-ray, and gamma ray. Among these seven, only light is perceived by the human eye, thus called visible light. 

 

Is light a wave?

 

Yes! Light is a wave. Light is an electromagnetic wave! It is a transverse wave but since it is an electromagnetic wave, it does not need a medium to propagate (unlike mechanical waves!) If fact, all electromagnetic waves are composed of two transverse waves that are oscillating perpendicular to each other. These oscillating transverse waves are electric fields and magnetic fields which oscillate perpendicular to each other.

 

The wave property of light is in fact proposed by Christian Huygens. His claim that light is a wave is supported by the result of the Double Slit Experiment conducted by Thomas Young!

 

But is it true that light is also a particle?

 

Prior to the wave theory of light, many scientists believed that light has particle nature. Sir Isaac Newton theorized that light is composed of streams of particles which he called corpuscles – thus the theory called Corpuscular Theory of Light! He theorized that these particles are emitted by light sources and spread outward in straight lines. The particle theory of light is supported by the Photoelectric Effect which is explained by Albert Einstein.

 

Both particle and wave nature is exhibited by light as discussed by the Wave-Particle Duality of Louis de Broglie. Today, light is known to be an electromagnetic wave. Since it is an electromagnetic wave, its speed is 3.0 x 10⁸ (or 300,000,000) meters per second!

Is light a form of energy?

 

Light carries energy! The energy of an electromagnetic wave is called quanta! (singular = quantum). Instead of continuous range of energy, Max Planck explained that the energy of EM waves is present in discrete amount of energy (or multiples of a specific amount of energy) called quanta. In short, quanta are packets of energy of EM waves. In light, these packets of energy are called photons.

 

Why do colors have energy?

 

When light passed through a prism, the colors of light (red, orange, yellow, green, blue, indigo, and violet) disperse creating a color spectrum we call as ROYGBIV! Since light is a wave, it has wavelength and frequency. The wavelength of light wave decreases from red to violet. This means that red has the longest wavelength in the color spectrum while violet has the least.

 

Wavelength and frequency are inversely proportional to each other. As wavelength increases, frequency decreases. Since red has the greatest wavelength, it follows that it has the least frequency. On the other hand, violet having the shortest wavelength has the highest frequency.

 

Each color of the electromagnetic spectrum carries energy. The energy carried by the EM wave is related to the frequency of the wave. The higher the frequency of electromagnetic wave, the higher is its energy! Since red has the lowest frequency, it also has the least amount of energy. Violet on the other hand has the greatest energy! This explains why blue is much hotter than red!

 

In an experiment for example where six thermometers are wrapped with colored plastics and exposed at the same time to intense heat source, the thermometer wrapped with red plastic will record the least temperature while the one wrapped with violet will record the highest.