A Rubens tube, also known as a standing wave flame tube, or simply flame tube, is a physics apparatus for demonstrating acoustic standing waves in a tube. Invented by German physicist Heinrich Rubens in 1905, it graphically shows the relationship between sound waves and sound pressure, as a primitive oscilloscope. Today, it is used only occasionally, typically as a demonstration in physics education.
A length of pipe is perforated along the top and sealed at both ends - one seal is attached to a small speaker or frequency generator, the other to a supply of a flammable gas (propane tank). The pipe is filled with the gas, and the gas leaking from the perforations is lit. If a suitable constant frequency is used, a standing wave can form within the tube. When the speaker is turned on, the standing wave will create points with oscillating (higher and lower) pressure and points with constant pressure (pressure nodes) along the tube. Where there is oscillating pressure due to the sound waves, less gas will escape from the perforations in the tube, and the flames will be lower at those points. At the pressure nodes, the flames are higher. At the end of the tube gas molecule velocity is zero and oscillating pressure is maximal, thus low flames are observed. It is possible to determine the wavelength from the flame minimum and maximum by simply measuring with a ruler.
Since the time averaged pressure is equal at all points of the tube, it is not straightforward to explain the different flame heights. The flame height is proportional to the gas flow as shown in the figure. Based on Bernoulli's principle, the gas flow is proportional to the square root of the pressure difference between the inside and outside of the tube. This is shown in the figure for a tube without standing sound wave. Based on this argument, the flame height depends non-linearly on the local, time-dependent pressure. The time average of the flow is reduced at the points with oscillating pressure and thus flames are lower. [1]
Heinrich Rubens was a German physicist born in 1865. Though he worked with better remembered physicists such as Max Planck at the University of Berlin on some of the ground work for quantum physics, he is best known for his flame tube, which was demonstrated in 1905. This original Rubens tube was a four-meter section of pipe with approximately 100 holes of 2 mm diameter spaced evenly along its length. [2]
When the ends of the pipe are sealed and a flammable gas is pumped into the device, the escaping gas can be lit to form a row of flames of roughly equal size. When sound is applied from one end by means of a loudspeaker, internal pressure will change along the length of the tube. If the sound is of a frequency that produces standing waves, the wavelength will be visible in the series of flames, with the tallest flames occurring at pressure nodes, and the lowest flames occurring at pressure antinodes. The pressure antinodes correspond to the locations with the highest amount of compression and rarefaction. [1]
The Guinness record for longest Rubens tube was achieved in 2019, when science show Kvark built a 10 meter Rubens tube at Saku Suurhall. [3]
A Rubens tube was on display at The Exploratory in Bristol, England until it closed in 1999. A similar exhibit using polystyrene beads instead of flames featured in the At-Bristol science centre until 2009. [4] Students make models of Rubens tube at their school science exhibition.
This display is also found in physics departments at a number of universities. [5] A number of physics shows also have one, such as: Rino Foundation [6] (The Netherlands), Fysikshow Aarhus (Denmark), Fizika Ekspres (Croatia) and ÅA Physics show (Finland). [7] [8]
The MythBusters also included a demonstration on their "Voice Flame Extinguisher" episode in 2007. [9] The Daily Planet's The Greatest Show Ever, [10] ran a competition whereby five Canadian science centres competed for the best science centre's experiment/display. Edmonton's Science Centre (Telus World of Science) utilized a Rubens tube, and won the competition. The special was filmed on October 10, 2010. Tim Shaw on the show Street Genius on National Geographic Channel also featured one in Episode 18 "Wave of fire".
The artist Emer O'Brien used Rubens tubes as the basis for the sound sculpture featured in her 2012 exhibition Return to Normal at the Wapping Project in London. [11]
A 2D Rubens tube, also known as a pyro board, is a plane of Bunsen burners that can demonstrate an acoustic standing wave in two dimensions. Similar to its predecessor, the one dimensional Rubens tube, this standing wave is caused by a multitude of factors. Pressure variation caused by the inflow of propane gas interfering with the input of sound waves into the plane causes changes in the height and color of the flames. The 2D Rubens tube was made famous by a Danish science demonstrator group in Denmark called Fysikshow. [12]
A 2D Rubens tube is made up of a lot of different parts. The main part itself is the rectangular steel box that outputs the propane gas. Steel is generally used for the plane on pyro boards because the compound can generally withstand immense amounts of heat and still be able to maintain its structure. Holes are drilled on the top of the steel plane to output the propane gas that is being constantly and slowly pumped into the steel box. [13] Instead of having a complete steel box, some pyro boards designs have wooden sides to support the steel plane on top. In wooden-style pyro boards, the interior of the box is usually covered with some sort of heat-resistant membrane that prevents the propane inside the box from leaking.
On the sides of the steel box are speakers that input a sound into the contained medium. The rate at which the propane gas escapes through the holes on the top of the pyro board is dependent on the intensity of the inputted sound. This relationship is directly proportional, meaning as the intensity of the sound increases, the rate at which the propane gas escapes increases.
Since the medium inside the steel box is kept at a constant volume, a standing wave has the ability to be produced. The frequency at which the standing wave can be produced is largely dependent on the physical dimensions of the box and the wavelength of the wave. Since pyro boards range in sizes, each board has its own unique frequencies at which a standing wave can be produced.
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, troughs, or zero crossings. Wavelength is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. The inverse of the wavelength is called the spatial frequency. Wavelength is commonly designated by the Greek letter lambda (λ). The term "wavelength" is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.
In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance of one or more quantities. Periodic waves oscillate repeatedly about an equilibrium (resting) value at some frequency. When the entire waveform moves in one direction, it is said to be a travelling wave; by contrast, a pair of superimposed periodic waves traveling in opposite directions makes a standing wave. In a standing wave, the amplitude of vibration has nulls at some positions where the wave amplitude appears smaller or even zero.
In physics, a standing wave, also known as a stationary wave, is a wave that oscillates in time but whose peak amplitude profile does not move in space. The peak amplitude of the wave oscillations at any point in space is constant with respect to time, and the oscillations at different points throughout the wave are in phase. The locations at which the absolute value of the amplitude is minimum are called nodes, and the locations where the absolute value of the amplitude is maximum are called antinodes.
In physics, a transverse wave is a wave that oscillates perpendicularly to the direction of the wave's advance. In contrast, a longitudinal wave travels in the direction of its oscillations. All waves move energy from place to place without transporting the matter in the transmission medium if there is one. Electromagnetic waves are transverse without requiring a medium. The designation “transverse” indicates the direction of the wave is perpendicular to the displacement of the particles of the medium through which it passes, or in the case of EM waves, the oscillation is perpendicular to the direction of the wave.
A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. The oscillations in a resonator can be either electromagnetic or mechanical. Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones. Another example is quartz crystals used in electronic devices such as radio transmitters and quartz watches to produce oscillations of very precise frequency.
Thermoacoustics is the interaction between temperature, density and pressure variations of acoustic waves. Thermoacoustic heat engines can readily be driven using solar energy or waste heat and they can be controlled using proportional control. They can use heat available at low temperatures which makes it ideal for heat recovery and low power applications. The components included in thermoacoustic engines are usually very simple compared to conventional engines. The device can easily be controlled and maintained.
The Rijke tube is a cylindrical tube with both ends open, inside of which a heat source is placed that turns heat into sound, by creating a self-amplifying standing wave, due to thermo-acoustic instability. It is an entertaining phenomenon in acoustics and is an excellent example of resonance.
A node is a point along a standing wave where the wave has minimum amplitude. For instance, in a vibrating guitar string, the ends of the string are nodes. By changing the position of the end node through frets, the guitarist changes the effective length of the vibrating string and thereby the note played. The opposite of a node is an anti-node, a point where the amplitude of the standing wave is at maximum. These occur midway between the nodes.
In electronics, a Lecher line or Lecher wires is a pair of parallel wires or rods that were used to measure the wavelength of radio waves, mainly at VHF, UHF and microwave frequencies. They form a short length of balanced transmission line. When attached to a source of radio-frequency power such as a radio transmitter, the radio waves form standing waves along their length. By sliding a conductive bar that bridges the two wires along their length, the length of the waves can be physically measured. Austrian physicist Ernst Lecher, improving on techniques used by Oliver Lodge and Heinrich Hertz, developed this method of measuring wavelength around 1888. Lecher lines were used as frequency measuring devices until inexpensive frequency counters became available after World War 2. They were also used as components, often called "resonant stubs", in VHF, UHF and microwave radio equipment such as transmitters, radar sets, and television sets, serving as tank circuits, filters, and impedance-matching devices. They are used at frequencies between HF/VHF, where lumped components are used, and UHF/SHF, where resonant cavities are more practical.
Acoustic resonance is a phenomenon in which an acoustic system amplifies sound waves whose frequency matches one of its own natural frequencies of vibration.
Kundt's tube is an experimental acoustical apparatus invented in 1866 by German physicist August Kundt for the measurement of the speed of sound in a gas or a solid rod. The experiment is still taught today due to its ability to demonstrate longitudinal waves in a gas. It is used today only for demonstrating standing waves and acoustical forces.
A loudspeaker enclosure or loudspeaker cabinet is an enclosure in which speaker drivers and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4-inch (10 cm) woofers and small tweeters designed for listening to music with a hi-fi system in a private home to huge, heavy subwoofer enclosures with multiple 18-inch (46 cm) or even 21-inch (53 cm) speakers in huge enclosures which are designed for use in stadium concert sound reinforcement systems for rock music concerts.
A propane torch is a tool normally used for the application of flame or heat which uses propane, a hydrocarbon gas, for its fuel and ambient air as its combustion medium. Propane is one of a group of by-products of the natural gas and petroleum industries known as liquefied petroleum gas (LPG). Propane and other fuel torches are most commonly used in the manufacturing, construction and metal-working industries.
A point source is a single identifiable localised source of something. A point source has negligible extent, distinguishing it from other source geometries. Sources are called point sources because in mathematical modeling, these sources can usually be approximated as a mathematical point to simplify analysis.
Whenever a wave forms through a medium/object with a closed/open end, there is a chance of error in the formation of the wave, i.e. it may not actually start from the opening of the object but instead before the opening, thus resulting on an error when studying it theoretically. Hence an end correction is sometimes required to appropriately study its properties. The end correction depends on the radius of the object.
An ultrasonic grating is a type of diffraction grating produced by the interference of ultrasonic waves in a medium, which alters the physical properties of the medium in a grid-like pattern. The term acoustic grating is a more general term that includes operation at audible frequencies.
In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimeters (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.
Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.
A wind instrument is a musical instrument that contains some type of resonator in which a column of air is set into vibration by the player blowing into a mouthpiece set at or near the end of the resonator. The pitch of the vibration is determined by the length of the tube and by manual modifications of the effective length of the vibrating column of air. In the case of some wind instruments, sound is produced by blowing through a reed; others require buzzing into a metal mouthpiece, while yet others require the player to blow into a hole at an edge, which splits the air column and creates the sound.
Sonoluminescence is a phenomenon that occurs when a small gas bubble is acoustically suspended and periodically driven in a liquid solution at ultrasonic frequencies, resulting in bubble collapse, cavitation, and light emission. The thermal energy that is released from the bubble collapse is so great that it can cause weak light emission. The mechanism of the light emission remains uncertain, but some of the current theories, which are categorized under either thermal or electrical processes, are Bremsstrahlung radiation, argon rectification hypothesis, and hot spot. Some researchers are beginning to favor thermal process explanations as temperature differences have consistently been observed with different methods of spectral analysis. In order to understand the light emission mechanism, it is important to know what is happening in the bubble's interior and at the bubble's surface.
Quote in German: "Eine geradlinige reihe von etwa 100 löchern von 2 mm weite.": "A straight line of about 100 holes 2 mm wide."
