Do you know why flame is multicolored?

Prof. Know Why answers:

Flame color depends on several factors, mainly oxygen supply, generated heat, carbon particles and the burning material with the movement of electrons in the metal ions. Thus all flame colors are not the same and different flames have different colors, like the flame color of a candle is different from the flame colors of a burning wood or a gas burner.

Each flame is multicolored, being mostly blue at the bottom, then orange or yellow and finally black at the top. The blue color signifies the hottest temperature zone of any flame. Since fire needs oxygen to burn, and as the bottom of the flame does not get much oxygen, it is the hottest spot in the flame and is blue in color. The flame gradually cools and changes color as it moves away from its source, because it is exposed to more oxygen. The temperature change causes the color of the flame to turn from blue at the hottest lower portion, to the typical bright yellowish-orange or bright orange color at the upper part. The shade of orange at the upper portion of the flame (where the flame is the coolest) depends upon the material being burned. The product of the burnt carbon, when it has cooled, is black soot, and comprises the top part of the flame.

Now, if we get into a little bit of physics, we will understand the scientific reasoning behind the color of a flame. When a material is heated, the electrons gain energy and jump to a higher level. However, they jump back to their initial level to maintain the stability. For this, each of these electrons releases the excess energy. Each jump involves a specific amount of energy being released as light energy, and each corresponds to a particular color. As a result of all these jumps, a spectrum of colored lines is formed. The color you see is the combination of all these individual colors. The exact sizes of the possible jumps in terms of energy vary from one metal ion to another. This means each ion will have a different pattern of spectral lines, and thus a different flame color.

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Do you know why we see a rainbow?

Prof. Know Why explains:

Witnessing the history, throughout the ages, mankind has always been fascinated by rainbows. And their arched splashes of color have been the subject of numerous songs and poems, stories and mythology. Even, in the Bible, the rainbow is seen as a sign of God's promises.

What makes rainbows so mysterious is the simple but often puzzling fact that rainbows are light and they exist only in the eyes of the beholder! To unlock this amazing secret of the nature and explore how water and light work together to produce the magnificent colorful work of art, we have to understand a little bit of physics, because that’s what it is – pure science!

You need three factors to work together to see a rainbow. Firstly, the sun must be shining. Secondly, the sun must be behind you, and thirdly, the air in front of you must have water drops in it. When the sunlight enters a water drop, it is refracted, or bent, and reflected out from the drop in such a way that the light appears as a spectrum of colors. Actually, the rays of light bend twice. As they enter the drops, the rays of light bend, then reflect off the back of the drops. Then they bend again, this time while exiting the drops. That's when the light appears before our eyes. Each drop reflects only one color of light, so there must be many water drops to make a full rainbow. You'll see the brightest rainbows when the water drops are large, usually right after a rain shower.

When a raindrop bends light, the light exits the raindrop at an angle of 40 to 42 degrees away from the angle it entered the raindrop. As a result, the only beams of light you see are from raindrops that are 40 to 42 degrees away from the shadow of your head. This gives the rainbow its curved appearance.

Do you know why the sky is blue?

Prof. Know Why explains:

The atoms of nitrogen and oxygen in the atmosphere separate the sun’s white light into its many colors and scatter them throughout the atmosphere. The wavelength of the blue light scatters better than the rest, predominating over other colors in the light spectrum. This makes the sky appear blue to us on a clear day.

The scientific name for this phenomenon is ‘Tyndall Effect’, more commonly known as ‘Rayleigh Scattering’. This phenomenon describes the way in which light physically scatters, when it passes through particles in the earths atmosphere that are 1/10th in diameter of the color of light. The light spectrum ranges in wavelength from red to violet and since the wavelength of the blue light passes through the particles with greater ease than the wavelengths of other colors of light, the sky appears blue to the naked eye.

The human eye has three types of light receptors, known as cones, located in the retina. The cones are either considered to be red or blue or green, based upon their strong response to light at these wavelengths. As light stimulates these receptors, our vision translates the signals into the colors we see. The skylight stimulates the red and green cones almost equally, while stimulating the blue cones more strongly, resulting in the blue colour of the sky.