Jessie Taylor
Candles have been the subject of scientific fascination for centuries, with scientists like Michael Faraday giving lectures on the chemical history of a candle as early as 1860. Candle flames have a distinct appearance, with a blue area at the base, a small dark orange-brown section in the middle, and a large yellow region at the top. The yellow colour is due to the flame's relatively low temperature, and the blue colour at the base is caused by the discrete emission spectra of molecular radicals produced by the breakdown of wax particles. Candle flames also emit a significant amount of infrared radiation, and their behaviour in microgravity has been studied by NASA, revealing that they take on a spherical shape due to the absence of convection currents.
| Characteristics | Values |
|---|---|
| Flame colour | Yellow, orange, or brown |
| Base colour | Blue |
| Shape on Earth | Elongated |
| Shape in microgravity | Spherical |
| Temperature | Relatively low |
| Heat radiation | In all directions |
| Infrared radiation | High |
| Cause of flickering | Incomplete combustion |
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What You'll Learn
Candle flames emit more infrared radiation than a cat
Candle flames emit more infrared radiation than cats. This is because candle flames are much hotter than cats, and when viewed through an infrared camera, they appear bright. The emitted spectra depend on the temperature of the object. Since candle flames burn at a relatively low temperature, they usually emit light in the yellow to orange range. The blue base of the flame is due to the discrete emission spectra of molecular radicals produced by the breakdown of wax particles. This blue light is also present in candle flames on Earth, but it is less bright than the yellow light from soot.
Soot is a byproduct of incomplete combustion, and it absorbs light at all frequencies, resulting in a smooth blackbody spectrum. When a candle flickers, the wisps of smoke are unburned soot particles that escaped from the flame. The yellow region of the flame is where the wax vaporizes and breaks down into hydrogen and carbon atoms. The hydrogen reacts with oxygen to form water vapour, and some of the carbon burns to form carbon dioxide.
In contrast, cats have a lower temperature than candle flames and emit less infrared radiation. Cats have a higher mass than candle flames, but this does not affect the amount of infrared radiation emitted. The temperature of an object is more important than its mass in determining the amount of infrared radiation emitted.
The behaviour of candle flames in microgravity has also been studied by NASA scientists. In microgravity, candle flames take on a spherical shape due to the absence of convection currents. These experiments contribute to our understanding of candle flames, combustion, and emissions.
Overall, candle flames emit more infrared radiation than cats due to their higher temperature, and this difference is visible through infrared cameras.
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Candle flames are not very hot, so most energy is released as infrared
Candle flames are not very hot, with the hottest part of the flame, the blue area at the base, burning at around 1,000°C (1,400°F to 1,800°F). The yellow part of the flame is cooler, often around 1,200°F, and the outermost part (red to orange in colour) is the coolest area, with temperatures around 800°F to 1,000°F. Due to their relatively low temperature, most of the energy from candle flames is released as infrared radiation.
The temperature of a candle flame can vary depending on several factors, including the type of wax, the size and material of the wick, and the ambient air temperature. The temperature also varies depending on which part of the flame is being measured. The flame is hottest at the base, where there is the most oxygen, and the temperature decreases as you move further away.
The colour of a candle flame is also influenced by temperature. A candle flame appears yellow because the yellow portion of the spectrum is the most dominant when the carbon ignites. If the temperature were increased, the flame would appear blue, as the blue colour is produced by discrete emission spectra of the molecular radicals produced by the wax particles breaking down. There is more of these molecular radicals near the base of the flame, which is why the base of the flame appears blue.
The light produced by a candle is a byproduct of combustion, which occurs when the heat of the flame vaporises the liquid wax, breaking down the hydrocarbons into molecules of hydrogen and carbon. These vaporised molecules react with oxygen from the air to create heat, light, water vapour, and carbon dioxide. The amount of heat created is enough to radiate back and melt more wax to keep the combustion process going until the fuel is used up or the heat is eliminated.
To prevent a candle flame from getting too hot, it is important to follow proper wick maintenance. Trimming the wick regularly will prevent the flame from getting too tall and hot. Additionally, it is important to always use caution when handling a burning candle and to avoid touching the flame or the molten wax, as they can cause burns.
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The blue base of a candle flame is due to discrete emission spectra
The blue base of a candle flame is due to the discrete emission spectra of the molecular radicals produced by the breakdown of wax particles. As the wax in a candle burns, it produces heat, causing the wax particles to vaporize and break down into molecular radicals. These molecular radicals emit light at specific wavelengths, resulting in the blue colour observed at the base of the flame.
The colour of a flame is influenced by its temperature and the presence of certain compounds. Candle flames typically burn at a relatively low temperature, resulting in the emission of yellow or orange light, which is characteristic of blackbody radiation from soot particles. Soot is formed when carbon radicals, which are highly reactive, bond together. However, in the lower part of the flame, there is a higher concentration of oxygen, which allows more carbon to react and prevents the formation of soot. As a result, the blue colour of the flame's base is attributed to the discrete emission spectra of these unreacted carbon radicals.
The blue colour at the base of a candle flame is not due to high temperatures causing a peak in the blackbody spectrum in the blue region. Instead, it is a result of the discrete emission spectra of the molecular radicals produced by the breakdown of wax particles. This phenomenon is similar to the discrete peaks observed in the blue flame of a butane torch, which is devoid of soot.
The oxygen saturation in the lower region of the flame also plays a role in the blue colour. The higher oxygen availability ensures that most of the carbon reacts, preventing the formation of compounds like C or CO, which are responsible for the yellow flame colour. Therefore, the combination of oxygen saturation and the presence of unreacted carbon radicals contributes to the blue emission spectra observed at the base of a candle flame.
Additionally, the shape and structure of the candle flame influence the distribution of colours. The bottom part of the flame, closer to the wick, is responsible for melting the wax and creating a gas phase around the wick's tip. This "reducing" part of the flame has a lower temperature compared to the upper regions, contributing to the yellow or orange light typically observed in candle flames. However, the discrete emission spectra of the molecular radicals at the base of the flame result in the distinct blue colour observed in that specific region.
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Candle flames in microgravity are spherical
Candle flames are not very hot, so most of their energy is released as infrared radiation. Since humans can only see the red-yellow portion of this spectrum, candle flames usually appear yellowish. In microgravity, however, candle flames behave differently.
On Earth, gravity-driven buoyant convection causes a candle flame to be teardrop-shaped and carries soot to the flame's tip, which makes it yellow. In microgravity, where convective flows are absent, the flame is spherical, soot-free, and blue. This is because the blue colour is produced by discrete emission spectra of the molecular radicals produced by the wax particles breaking down. There are more of these particles near the base of the flame, so the base appears blue.
The absence of buoyant convection in microgravity also means that the transport of combustion products and oxygen occurs by the much slower process of molecular diffusion. This diffusion occurs when there are high concentrations of combustion products and low concentrations of oxygen close to the flame, and a high concentration of oxygen farther away from the flame. As a result, a flame in microgravity will often appear to burn less vigorously than a flame on Earth, and it will assume a spherical shape that diffuses equally in all directions.
NASA has conducted experiments on candle flames in microgravity using drop towers and the Space Shuttle during the USML-1 mission in June 1992. These experiments showed that immediately after ignition, the candle flame was spherical and bright yellow. After 8-10 seconds, the yellow colour, presumably from soot, disappeared, and the flame became blue and nearly hemispherical.
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The colour of a candle flame depends on its temperature
The temperature of a candle flame varies across its structure. The blue area at the base of the flame is the hottest zone, where the hydrocarbon molecules in the wax vaporize and break down into hydrogen and carbon atoms. The hydrogen atoms react with oxygen to form water vapour, and some of the carbon burns to form carbon dioxide.
Above the blue zone is a small dark orange-brown section, where there is a relative lack of oxygen. Here, the various forms of carbon continue to break down, and small, hardened carbon particles, or soot, begin to form. These particles are carried upwards, along with the water vapour and carbon dioxide, and are heated to around 1000°C.
The large yellow region at the top of the flame is the coolest part, and it is the colour that we typically associate with candle flames. The yellow colour is due to the blackbody radiation from the soot particles, which absorb light at all frequencies. When heated, these particles emit a smooth blackbody spectrum, resulting in the characteristic yellow colour of candle flames.
The colour of a candle flame can also be influenced by its environment. For example, in the late 1990s, NASA scientists conducted experiments to observe how candle flames behaved in microgravity. They found that in the absence of gravity, the warm air had no upward direction to create a convection current, resulting in a spherical flame shape instead of the elongated shape typical of candle flames on Earth.
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Frequently asked questions
Candle flames emit a lot of infrared radiation, and since they burn at a relatively low temperature, they tend to appear yellow or orange.
Candle flames are not very hot, so most of their energy is released as infrared to yellow light. Since humans can only see the red-yellow portion of that light, candle flames appear yellowish.
The blue area at the base of a candle flame is where hydrocarbon molecules vaporize and break apart into hydrogen and carbon atoms. The hydrogen reacts with oxygen to form water vapour, and some of the carbon burns to form carbon dioxide.
The blue colour is produced by discrete emission spectra of the molecular radicals produced by the wax particles breaking down. Since there are more of these molecules at the base of the flame, it appears blue.
Yes, in microgravity, candle flames become spherical instead of their elongated shape on Earth. Without gravity, there is no upward direction for warm air to rise and create a convection current.
