This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Magnetostriction Effect and Magnetostriction Generator”.
1. Which of the following effects can be used to produce ultrasonic waves?
a) Magnetostriction effect
b) Doppler Effect
c) Magnetic effect
d) Sound effect
Explanation: When an alternating magnetic field is applied to a ferromagnetic material, then the rod is thrown into vibrations, thereby producing ultrasonic waves at resonance. Therefore ultrasonic waves can be produced using magnetostriction effect.
2. It is not possible to get a constant single frequency using magnetostriction effect.
Explanation: It is not possible to get a constant single frequency using magnetostriction method because it depends on the temperature.
3. When is ultrasonic waves produced using piezo electric oscillator?
a) At constant temperature
b) At resonance
c) At constant pressure
d) At constant voltage
Explanation: Piezo electric oscillators produce ultrasonic waves at resonance. That is when the frequency of the oscillatory circuit is equal to the frequency of the vibrating crystal.
4. Which of the following causes acoustical grating?
a) Magnetic waves
b) Electric waves
c) Magnetostriction effect
d) Ultrasonic waves
Explanation: When ultrasonic waves are passed through a liquid, the density varies layer by layer due to the variation in pressure and hence the liquid will act as a diffraction grating called acoustical grating.
5. What is the principle for measurement of the velocity of ultrasonic waves?
a) Magnetostriction effect
b) Acoustical grating
c) Doppler Effect
d) Acceleration effect
Explanation: When ultrasonic waves are passed through a liquid, due to variation in pressure, the liquid will act as diffraction grating called acoustical grating. Under this condition when a monochromatic light is passed through the acoustical grating, the light gets diffracted. By using this velocity can be determined.
6. What is cold welding?
a) Welding at very low temperature
b) Welding using ultrasonic waves
c) Welding under water
d) Welding at constant temperature
Explanation: Some materials cannot be welded at high temperature. In such cases, the welding can be done at room temperature using ultrasonics and is called cold welding.
7. What is the other name for ultrasonic flaw detector?
a) Destructive testing
b) Magnetostrictive testing
c) Non-destructive testing
d) Echo testing
Explanation: Whenever there is a change in medium, then the ultrasonic waves will be reflected. Thus, from the intensity of the reflected echoes, the flaws are detected without destroying the material and hence this method is known as a non-destructive testing method.
8. Sonograms work under the principle of Doppler Effect.
Explanation: There is an apparent change is the frequency between the incident sound waves on the foetus and the reflected sound waves from the foetus. Therefore it works on the principle of Doppler Effect.
9. A quartz crystal of thickness 0.001m is vibrating at resonance. Calculate the fundamental frequency. Density of quartz = 2.650×103 kg/m3 and Young’s modulus for quartz = 7.9×1010 N/m2.
Explanation: Fundamental frequency = 1/(2×0.001) √((7.9×1010)/(2.650×10-3))
Fundamental frequency = 2.7299×106MHz.
10. An ultrasound pulse sent by a source in sea is reflected by a submerged target at a distance 597.50m and reaches the source after 0.83seconds. Find the velocity of sound in sea water.
Explanation: Velocity = 2d/t
Velocity = 1439.75m/s.
Sanfoundry Global Education & Learning Series – Engineering Physics.
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