BANNARI AMMAN INSTITUTE OF TECHNOLOGY SATHYAMANGALAM DEPARTMENT OF PHYSICAL SCIENCES Unit III ULTRASONICS

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1 A1 A2 A3 A4 A5 A6 A7 A8 A9 BANNARI AMMAN INSTITUTE OF TECHNOLOGY SATHYAMANGALAM DEPARTMENT OF PHYSICAL SCIENCES Unit III ULTRASONICS Multiple Choice Questions Loudspeaker cannot produce ultrasonic waves due to a) resonance b) high mechanical inertia c) acoustic impedance d) pressure Ultrasonic waves a) require a medium for their propagation b) have the frequencies in between 20 Hz and 20 khz c) require no medium for their propagation d) can be produced by an organ pipe The wavelength of ultrasonic waves in air is in the order of a) 1 cm b) cm c) cm d) cm The audible range of frequency for human being is a) Hz b) >20000 Hz c) 20 Hz 20 khz d) 20 Hz khz Which of the following frequency lies in the range of ultrasonic waves? a) 10 khz b) 5 khz c) 1 khz d) 1 MHz The principle used for the production of ultrasonic waves is a) photoelectric effect b) inverse piezoelectric effect c) Hall effect d) piezoelectric effect Ultrasonic waves are detected by using a) magnetostriction b) Kundt s tube method c) Interferometer d) photo detectors The velocity of ultrasonic waves in air is a) 120 m/s b) 4200 m/s c) 330 m/s d) 3 x 10 8 m/s Piezoelectric oscillator generates ultrasonic frequency up to a) 500 Hz b) 500 khz c) 500 MHz d) 500 Giga Hz A10 Acoustic grating is used to find the sound velocity in a) gases, liquids and solids b) liquids and solids Page 1 of 5

2 c) solids and gases d) liquids only A11 Which among the following sound waves have highest velocity in air? a) infrasonics b) ultrasonics c) audible sounds d) all the sound waves have the same velocity A12 Ultrasonic waves do not travel through a) solids b) liquids c) gases d) vacuum A13 ultrasonic waves can be produced by using X-cut crystal a) longitudinal b) transverse c) partly longitudinal and partly transverse d) sometimes longitudinal and sometimes transverse A14 The technique used by bats to find their way and to locate the food is. a) Interference b) diffraction c) Echolocation d) flapping A15 An ultrasonic wave is sent from a ship towards the bottom of the sea. The time interval between sending and receiving of the wave is 1.6 s. Calculate the depth of the sea, if the velocity of sound in the seawater is 1400 m/s? a) 1120 m b) 560 m c) 1400 m d) 112 m A16 The relation between wave velocity 'v', frequency 'f ', and wavelength ' ' is a) v = f / b) v = f c) v = / f d) v = 1 / f A17 When transverse ultrasonic waves travel through solid, the particles. a) vibrate along the direction of wave b) vibrate but not in any fixed direction propagation c) vibrate perpendicular to the direction of wave propagation d) do not vibrate A18 Bats detect the obstacles in their path by receiving the reflected. a) infrasonic waves b) radio waves c) electro-magnetic waves d) ultrasonic waves A19 In SONAR, the time taken to receive the echo from the depth of the sea is measured as 0.67 s. The velocity of ultrasonic waves in the sea water is 1500 ms -1. Calculate the depth of the sea. a) m b) m c) 5022 m d) m A20 Magnetostriction oscillator can generate ultrasonic waves with frequency a) 100 Tera Hz b) 1000 khz Page 2 of 5

3 c) 100 MHz d) 100 Giga Hz A21 The change in dimensions occurs in a ferromagnetic material placed in the magnetic field parallel to its length is known as a) magnetostriction b) piezoelectric effect c) ferroelectricity d) inverse piezoelectric effect A22 The diffraction of ultrasonic waves is a) Moderate b) high c) negligible d) very high A23 Piezoelectric generators are used for the production of a) sound waves b) infrasonic waves c) ultrasonic waves d) radio waves A24 Ultrasonic waves have large energy due to their frequency a) low b) very low c) moderate d) high A25 Magnetostriction method is used for the production of waves a) audible b) ultrasonic c) infrasonic d) radio waves A26 The velocity of ultrasonic waves with the increase of frequency a) increases b) decreases c) moderate d) none of the above A27 Acronym for SONAR is a) sound navigation and ranging b) selection navigation and ranging c) source and navigation ranging d) sound navigation and reading A28 The principle of SONAR is a) echo-sound b) piezoelectric effect c) magnetostriction d) inverse piezoelectric effect A29 When a monochromatic light is passed through an acoustic grating, the light undergoes a) interference b) diffraction c) reflection d) absorption A30 Ultrasonic waves can be sensed by a) human beings b) Donkey c) Bats d) Horse Page 3 of 5

4 PART B B1. Classify sound waves based on frequency. B2. Ultrasonic waves are not electromagnetic waves. Justify. B3. High frequency ultrasonic waves cannot be generated using magnetostriction oscillator. Comment. B4. List four important properties of Ultrasonic waves. B5. State magnetostriction effect. B6. Mention the four methods of ultrasonic detection. B7. Define piezo-electric effect. B8. Differentiate piezo-electric and inverse piezo-electric effects B9. Calculate the natural frequency of 40 mm length of a pure iron rod. Given: The density of pure iron is 7.25x10 3 kg/m 3, Young s modulus is 115x10 9 N/m 2? B10. Define acoustic grating. B11. Nodes and anti-nodes in acoustic grating act like slit and ruling. Justify B12. Find the depth of submerged submarine if an ultrasonic wave is received after 0.33 s from the time of transmission. (given v=1400 m/s) B13. Compare the advantages of magnetostriction and piezo-electric oscillators. B14. List the four applications of SONAR. B15. Ultrasonic waves are not used in RADAR. Comment. B16. Mention the four medical applications of ultrasonics. B17. Identify the technique used in SONAR. B18. Copper rods cannot be used in a magnetostriction generator. Why? B19. Identify the measurement of velocity of blood flow using ultrasonic waves. B20. When ultrasonic waves are passed through liquids, cavitations are produced. Criticize. PART C C1. i Describe the production of ultrasonic waves by 8 Magnetostriction method. ii List two merits and demerits Magnetostriction method. 4 C2. Explain the principle, construction and working of the 12 Piezoelectric Oscillator for producing ultrasonic waves. C3. Illustrate three methods used to detect ultrasonic waves. 12 C4. With a neat diagram, discuss the theory and experiment to 12 determine the velocity of ultrasonic waves in a liquid. C5. i Discuss the disadvantages of magnetostriction oscillator. 4 Page 4 of 5

5 ii Explain how SONAR is employed to locate the objects 8 C6. Explain the fetal heart movement and blood circulation using ultrasonics. 12 Page 5 of 5