How to Measure the Velocity of Sound in a Quincke Tube

Quincke devised a simple method of measuring the velocity of sound by obtaining permanent interference between two sound waves. He used a closed tube, now known as the Quinke tube,  SAEB which had openings at S, E, and placed a source of sound at S. A wave then traveled in the direction SAE round the tube, while another wave traveled in the opposite direction SBE; and since these waves are due to the same source, S, they always set out in phase, i.e., they are coherent.

Like a trombone, one side, b, of the tube can be pulled out, thus making SAE, SBE of different lengths. When SAE and SBE are equal in length an observer as E hears a loud sound, since the paths of the two waves are then equal. As B is pulled out the sound dies away and becomes a minimum when the path difference, SBE-SAE, is λ/2, where λ is the wavelength. In this case the two waves arrive 180⁰ out of phase. If the tube is pulled out farther, the sound increases in loudness to a maximum; the path difference is then λ. If k is the distance moved from one position of minimum sound, MN say, to the next position of minimum sound, PQ say, then 2k = λ. Thus the wavelength of the sound can be simply obtained by measuring k.

The velocity of sound in the tube is given v = f λ, where f is the frequency of the source s, and thus v can be found when a source of known frequency is used. In a particular experiment with Qunicke’s tube, the tube B was moved a distance 4.28cm between successive minima of sound, and the frequency of the source was 400 Hz.

Thus          λ = 2 x 4.28cm

and   v = fλ = 4000 x 2 x 4.28 = 34240cm s^-1 = 342.4ms^-1

 It can be seen that, unlike reflection and refraction, the phenomenon of interference can be utilized to measure the wavelength of sound waves and the velocity of sound. We shall see later that interference is also utilized to measure the wavelength of high waves.     

Destructive Interference

Consider now a point P whose distance from B is half a wavelength longer than its distance from A, i.e., AP-BP = λ/2. The vibration at P due to B will then be 180⁰ out of phase with the vibration there to A. the resultant effect at P is thus zero, as the displacements at any instant are equal and opposite to each other, no sound is therefore heard at P, and the permanent silence is said to be due to “destructive interference” between the sound waves from A and B.

If the path difference, AP – BP, were 3λ/2 or 5        λ/2, instead of λ/2, permanent silence would also exist at P as the vibrations, there due to A, B would again be 180⁰ out of phase. Summarizing, then,

          Silence occurs if the path-difference is an odd number of half wavelengths, and

          A loud sound occurs if the path- difference is a whole number of wavelengths.

The total sound energy in all the positions of loud sound discussed above is equal to the total sound energy of the two sources A, B, from the principle of the conservation of energy. The extra sound at the positions of loud sound thus makes up for the absent sound in the positions of silence.

Herschel-Quincke Tube

The Herschel-Quincke tube (HQ tube) can reduce duct-borne noise by the principle of wave cancellation caused by path length differences and reflections at junctions. However, the HQ tube has several drawbacks.

This article will introduce a modified Herschel-Quincke tube that overcomes these limitations. The apparatus has a shape of U and two limbs, one with very narrow width compared to the other.

Holmarc’s Magnetic Susceptibility – Quincke’s Method

Magnetic susceptibility is an estimate of the degree to which a substance will become magnetised in response to an applied magnetic field. This experimental measurement is used to classify substances as diamagnetic, paramagnetic or ferromagnetic. It is a fundamental property of materials and can be measured using a variety of methods. A few of the most commonly used methods are Gouy’s method and Quincke’s method.

Quincke’s method is an easy-to-use experimental technique for determining the magnetic susceptibility of a liquid or solution. It is a modification of the Gouy method and is specially designed for liquids. The technique is based on the force felt by a magnetised material in a non-uniform magnetic field. The method is named after German physicist Georg Hermann Quincke.

The apparatus consists of a U shaped tube with two limbs, one narrower than the other. The narrow part is placed in a uniform magnetic field, while the wider part is far away from it. The change in level of the liquid in the narrow limb is proportional to the magnitude of the magnetic field. When the magnetic field is removed, the level of the liquid returns to its initial position. The magnetic susceptibility of the sample is determined by comparing this value with the molar magnetic susceptibility of the solution.

This experiment can be performed at any temperature but the results will be most accurate at room temperature. The molar magnetic susceptibility of a solution is usually given in terms of its magnetic moment divided by its electric charge. For this reason, it is important to use a high-precision instrument for this type of measurement.

Holmarc’s Apparatus

Holmarc manufactures a wide range of scientific and engineering instruments to cater to the needs of research, industry, and education. These products include imaging instruments, measuring instruments, spectroscopy tools, analytical instruments, lab equipment, physics lab instruments, breadboard/table tops, opto-mechanical components, optics, linear and rotation stages, motorized linear and rotation stages, industrial automation solutions, and others. It also offers maintenance and modification support for these products. Its manufacturing facility in Kalamassery, Kanayanoor, Ernakulam in Kerala houses state-of-the-art machinery and equipment. Its team of professionals specializes in areas such as optics design, mechanical engineering, electrical R&D, and optical manufacturing.

The Hall Effect Apparatus from Holmarc can be used for the purpose of determining the conductivity of semiconducting materials. The instrument can be used to determine the Hall coefficient, concentration of charge carriers, mobility of charge carriers, and field dependence of a material. It is also able to find out the type of a semiconductor material. It is a highly advanced and easy-to-use equipment system that guarantees a simple experiment set up, a minimum preparation time, and a safe execution of the experiments.

This HO-ED-EM-040 Hall Effect Apparatus from Holmarc has an inbuilt source measure unit that helps the user to read the current passing through the sample and apply voltage to the sample. It has a user-friendly software that enables PC interfacing to regulate the features like syringe pump flow rate, spray duration, and rotating mandrel speed. It is equipped with HMPSKV30 model high voltage power supply that provides 0-30 kV output voltage range. The system hood has features like exhaust fan, halogen lighting and transparent door for monitoring the electrospinning process.

Moreover, Holmarc’s diverse product line may make it resilient to market changes, as it isn’t overly dependent on one single product segment. Additionally, the company is ISO certified and has implemented quality management systems that add to its credibility.

Quincke’s Apparatus

Quincke’s apparatus is a simple instrument that allows you to observe the effects of interference in sound waves. It consists of a resonance tube with a millimetre scale which is partially filled with water and is connected to an expansion vessel with a tube. The column of air above the water is stimulated to oscillate by a tuning fork (optionally a loudspeaker). By raising the expansion tank, the level of the water inside the tube can be raised, which shortens the height of the sound wave. This results in constructive or destructive interference.

Quinck’s methods were based on the ideas of Faraday. He also influenced Maxwell’s work on magnetic susceptibility and diamagnetic substances. His work was very influential in the nineteenth century, and his writings appeared in journals until his death in Heidelberg at age 89.

He was an expert on capillarity and devoted much of his life to the collection of data on the properties and constants of substances. His research was based on theories that viewed light as elastic vibrations in a mechanical medium. He used his knowledge of fluid mechanics to develop a method for measuring the changes in liquid levels caused by the application of magnetic fields.

The Quincke-Herschel interference tubes are a useful tool for analyzing noise produced by turbofan engines. These devices have been proposed as an alternative to duct baffles and diffusers, and have been shown to reduce noise production by up to 40 dB. However, these techniques require more rigorous engineering and testing. An analytical model for calculating the acoustic losses of Herschel-Quincke tubes has been developed. This model has been tested and validated using a computational fluid dynamics analysis of Herschel-Quincke tubes applied to circular inlets of turbofan engines. Results show that the theoretical loss is proportional to the radius of the inlet.