Physics Book

Application of Ultrasonic waves SONAR is a device which stands for sound navigation and ranging. It is based on the principle of echo sounding. In this acoustical technique highfrequency ultrasonic wave are used. When ultrasonic waves are transmitted through water , gets reflected by the object under water. The change in frequency of the echo signals due to the Doppler effect helps us to determine the velocity , distance and the direction of object. In the absence of an obstacle the ultrasonic waves do not get reflected to the receiving transducer. But in the presence of an obstacle the ultrasonic waves get reflected and are picked up by the receiving transducer. Knowing the velocity of ultrasound and the elapsed time, the distance of the object can be determined. Using SONAR, the distance and direction of submarines, depth of sea, depth of rocks in the sea, the shoul of fish in the sea, etc., can be determined. 1. Determinati  of Depth of Sea The ultraso

Determination of Velocity of Ultrasonic waves Principle When ultrasonic waves passed through transparent liquid medium in a container, the waves get reflected. These reflected waves are called echos. The direct and reflected waves superimpose to form the stationary wave pattern. These waves give rise to a periodic vibration in the density of the liquid. The change density of the liquid in turn leads to vibration in the refractive index of the liquid. The density of the liquid would be maximum at nodal planes, while at the antinodal planes, it would be minimum. Such a liquid column subjected ultrasonic waves behaves like a grating. Under this condition, if a parallel beam of light is passed through the liquid at right angles to the waves, the liquid acts as a diffraction grating. Such a grating is known as acoustic grating. Experiment Thee experimental arrangement is shown in figure. There is a glass vessel containing tho liquid with a reflector fixed within the

Presence of ultrasonic waves can be detected by using any one of the following methods: 1. Quartz crystal method This method of detecting ultrasonic waves is based on the principle of piezoelectric effect. When one pair of opposite faces of the quartz crystal is exposed to ultrasonic waves, in the other pair of opposite faces, charges get developed as shown in figure. These changes are amplified and detected using suitable electronic circuits. 2. Thermal detection method Principle When the ultrasonic waves are propagated through a medium, the temperature of the medium changes due to alternate compressions and rarefactions. In the case of stationery waves, there is a change in the temperature at nodes and no change in temperature at antinodes. Based on this principle, by sensing the change in temperature using suitable components, the ultrasonic waves can be detected. It is the most commonly used method to detect ultrasonic waves. In this method, a fine platinum wire

Piezoelectric Effect When pressure is applied to one pair of opposite faces of crystal like quartz, tourmaline, Rochelle salt, etc., cut with their faces perpendicular to its optic axis, equal and opposite charges appear across its other faces as shown in figure. This phenomenon is known as piezoelectric effect. The frequency of the developed emf is equal to the frequency of dynamic pressure. The sign of the charge gets reversed if the crystal is subjected to tension instead of pressure. The electricity produced by means of piezoelectric effect is called piezoelectricity . The material which can undergo piezoelectric effect is called piezoelectric material or crystal. Note: The type of crystal used for ultrasonic production is generally the X-cut crystal. An X-cut crystal is piezoelectric crystal cut in a direction perpendicular to its X-axes(Electrical axes). The cross-section of a natural quartz crystal is hexagonal. The lines joining the midpoint of the op

Magnetostriction Effect When a ferromagnetic material in the form of rod is subjected to an alternating magnetic field parallel to its length shown in figure, the rod undergoes alternate constructions and expansion at a frequency equal to the frequency of the applied magnetic field. This phenomenon is known as magnetostriction effect . Magnetostriction Effect Due to resonance the rod is thrown into longitudinal vibrations, thereby producing ultrasonic waves in the surrounding medium. Such ferromagnetic materials which are used for the production of ultrasonic waves are called  ' Magnetostriction materials '. Construction The circuit diagram is shown in figure. Circuit Diagram The ferromagnetic rod AB is clamped at the middle X. The coils L1 and L2 are wound at the ends of the rod. To the coil L1 a variable capacitor C1 is connected in parallel and this combination forms the resonator or tank circuit. One side of the resonator circuit is connec

 Ultrasonic waves Definition The sound waves of frequency greater than 20kHz are called ultrasonics waves. These sound waves are inaudible to human ear. The ultrasonic waves due to their shorter wavelength have a greater penetrating power. Ultrasonic waves are widely used in medical diagnostics, marine applications, NDT, etc. Properties of Ultrasonic waves The frequency of ultrasonic waves is greater than 20 kHz. Their wavelength are small. As a result, their penetrating power is high. They can travel over long distances as a high directional beam. They have high energy content. Their speed of propagation increases with increase in frequency. Production of Ultrasonic waves   Based on frequency range and power output, the ultrasonic waves generators divided into two groups: Mechanical generator Electrical generator The electrical generator are subdivided into two categories: Megnetostriction generator or oscillator Piezoelectric ge