Jessie Taylor
The famous experiment of lighting a candle underwater has intrigued many, especially children. The experiment involves lighting a candle and allowing it to float on water, then quickly placing a glass over it and submerging it. Surprisingly, the candle remains lit underwater, seemingly defying logic. This phenomenon can be explained by understanding the role of heat, oxygen, and the unique properties of water. The cool water surrounding the candle absorbs heat from the flame, preventing the wax from melting and allowing the candle to continue burning. Additionally, the limited oxygen supply under the glass eventually gets consumed, causing the flame to go out. This experiment showcases the fascinating interplay between fire, water, and the air we breathe.
| Characteristics | Values |
|---|---|
| Air inside the glass | Limited supply of oxygen |
| Flame | Produces heat |
| Gases in the glass | Expand when hot, contract when cold |
| Water | Rises when the gas in the glass cools and contracts |
| Thinner candle | Less heat, less noticeable expansion/contraction |
| Two candles | Twice the heat, more noticeable expansion/contraction |
| Oxygen | Gets consumed and turns into carbon dioxide |
| Carbon dioxide | Takes up less volume than oxygen |
| Wax | Stays solid due to cool water absorbing heat from the flame |
| Bowl | Should be the same height as the candle |
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What You'll Learn
The candle will eventually burn out when it uses up all the oxygen
The air inside the glass has a limited supply of oxygen. Once the oxygen is consumed, the flame will go out, and heat will stop being produced. This will cause the gas in the glass to cool and contract, resulting in water entering the glass to balance the pressure. The amount of oxygen or the rate of oxygen consumption is not the focus of this experiment. Instead, it is a physics experiment demonstrating the volume change of gas during heating and cooling.
The candle burning underwater may seem like magic, but it is a well-known science experiment. The water's ability to absorb heat energy is critical to the candle's continued burning. Cold water absorbs more heat energy, allowing the wax to remain solid and preventing it from melting or dripping onto the sides. This unusual behaviour of the candle is due to the heat from the flame being absorbed by the surrounding water.
The burning candle and rising water experiment demonstrate the relationship between gas pressure, volume, temperature, and the number of molecules. The pressure and temperatures at the beginning and end of the experiment remain relatively constant. However, the number of oxygen molecules is replaced by half as many carbon dioxide molecules, resulting in a corresponding volume decrease. This experiment also supports the van der Waals equation, which incorporates the size of the molecules.
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Water has the quality of absorbing heat energy
Water has the amazing quality of absorbing heat energy. In the underwater candle experiment, the water surrounding the candle absorbs the heat from the flame. This absorption of heat energy prevents the wax from melting or dripping, allowing the candle to stay lit. The heat produced by the flame causes the gases in the enclosed space to expand. However, once the flame goes out, the heat production stops, causing the gases to cool and contract. As a result, water enters the glass to balance the pressure.
The burning candle experiment demonstrates the transformation of heat energy. When a candle burns, it combines oxygen from the air with carbon and hydrogen in the wax to produce carbon dioxide, water vapour, and heat. The heat generated by the flame is absorbed by the water, reducing its impact on the outer surface of the candle. This absorption of heat energy by water is a fundamental concept in understanding the behaviour of heat transfer and the properties of water.
The amount of oxygen in the air plays a crucial role in the experiment. The limited supply of oxygen inside the enclosed space is eventually consumed, leading to the extinguishing of the flame. The depletion of oxygen is not solely responsible for the rise in water level, as the water rises rapidly after the candle goes out. This observation suggests that other factors, such as pressure and temperature changes, also influence the water level.
The experiment showcases the principles of physics and chemistry. The transformation of oxygen and hydrogen into water vapour and the production of carbon dioxide illustrate chemical reactions. Additionally, the expansion and contraction of gases due to temperature changes and the resulting pressure changes are fundamental concepts in physics. Understanding the behaviour of gases, heat transfer, and the unique properties of water are key takeaways from this experiment.
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The water level rises when the candle goes out
The famous lit candle experiment involves placing a burning candle under a glass on a plate of water. The candle continues to burn underwater, but eventually goes out. This experiment demonstrates several scientific principles.
Firstly, the air inside the glass has a limited supply of oxygen, which the flame consumes. As the flame produces heat, the gases in the glass expand. When the candle eventually goes out, it stops producing heat, causing the gas in the glass to cool and contract. This results in water entering the glass to balance the pressure.
The water in the experiment also plays a crucial role in the candle's burning behaviour. The cool water surrounding the candle absorbs the heat from the flame, preventing the wax from melting or dripping. This absorption of heat energy results in a lower impact on the outer surface of the candle, allowing it to continue burning underwater.
Additionally, the number of candles and their thickness influence the water level rise. Using thinner candles results in less heat production and less noticeable expansion and contraction of gases. Conversely, employing multiple candles generates more heat and causes a more noticeable volume change of gases.
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The air volume decreases and pulls the water up
When a candle is lit, it heats up the air around it, causing the air to expand and become less dense. This hot air rises, creating a current of air movement. In the context of the underwater candle experiment, as the candle burns inside the glass jar, the oxygen within the jar is consumed, which causes a decrease in air volume. This decrease in air volume leads to a reduction in pressure inside the jar.
According to Boyle's law, there is an inverse relationship between the pressure and volume of a gas. When the pressure inside the jar decreases, it creates a pressure difference between the inside and outside of the jar. The higher pressure outside the jar, which is the result of atmospheric pressure, pushes the water up and into the jar.
As the air volume above the water level in the jar decreases due to the burning of the candle, the pressure outside the jar becomes greater than the pressure inside. This pressure differential results in the water being literally pushed up into the jar to equalize the pressure. So, the water rises inside the jar, seemingly defying gravity, and surrounds the burning candle.
The rising water doesn't extinguish the flame because the candle has already heated the air inside the jar, making it less dense. As the candle continues to burn, it further heats the air, causing it to rise and escape through the neck of the jar. This creates a continuous flow of air, ensuring that the flame receives the necessary oxygen to stay lit.
The experiment showcases the interplay between several scientific principles, including the behaviour of gases, atmospheric pressure, and convection currents. It also highlights the importance of understanding pressure differentials and their effects on fluids, providing a fascinating demonstration of how science can offer surprising and counterintuitive results.
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The wax stays solid because the water absorbs the heat from the flame
The famous candle burning underwater experiment is a great way to demonstrate several scientific principles. The experiment involves lighting a candle and placing it under a glass of water, where it continues to burn. This may seem like magic, but there are several reasons why the candle stays lit.
Firstly, the air trapped inside the glass provides oxygen for the flame. The flame combines oxygen with carbon and hydrogen in the wax to form CO2, H2O, and heat. As the flame consumes oxygen, the volume of air decreases, creating a vacuum that pulls water up into the glass. This demonstrates the ideal gas law, which relates gas pressure, volume, temperature, and the number of molecules.
Secondly, the water plays a crucial role in keeping the flame burning. Water has the unique ability to absorb heat energy, and cold water absorbs even more heat. When the candle is submerged, the water absorbs the heat from the flame, preventing it from melting the wax. This allows the wax to stay solid, providing fuel for the flame to continue burning.
Additionally, the shape of the glass and the presence of a circular current within it ensure that oxygen from above the water is also drawn into the flame, prolonging its burn time. This experiment showcases the fascinating interplay between fire and water and provides a visual demonstration of the scientific principles governing combustion and heat transfer.
It is important to note that this experiment should be performed with safety precautions, such as wearing safety goggles and having adult supervision, especially when working with fire and hot water.
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Frequently asked questions
The candle stays lit underwater because the cool water surrounding the candle absorbs the heat from the flame, allowing the wax to stay solid. The air trapped inside the glass also provides oxygen to fuel the flame.
If left underwater, the candle will eventually burn out as it uses up all the oxygen trapped under the glass.
The burning candle combines oxygen from the air with carbon and hydrogen in the wax to form CO2, H2O, and heat. The heat produced causes the gases in the glass to expand, and when the flame goes out, the gas in the glass cools and contracts, causing water to enter the glass to balance the pressure.
