Important Questions and Answers: Acoustics and Ultrasonics

1.     How are sound waves classified?

Sound waves are classified into three categories.

a.     Infrasonic(below 20Hz)

b.     Audible Sound (between 20Hz and 20,000Hz )

c.      Ultrasound (above 20,000 Hz)

2.     Name the methods by which Ultrasonic waves

a.     Mechanical generators.

b.     Magnetostriction Generators or Oscillator

c.      Piezoelectric Generator or Oscillator

3.     What is the principle behind the Magnetostriction Oscillator? Or what is meant by Magnetostriction effect.

Magnetostriction effect is the principle o producing Ultrasonic waves by using Magnetostriction Oscillator.

When an alternating magnetic filed is applied to a rod of ferromagnetic rod such as Nickel, Iron or Cobalt, then the rod is thrown to longitudinal vibrations. When the frequency of the vibration rod is equal to the natural frequency of the vibration, Resonance occurs. This produces Ultrasonic waves.

4.     What is meant by Sonar?

SONAR is a device, which stands for Sound Navigation and Ranging. The principle of Sonar is based on the echo surrounding technique of Ultrasonics. It is the acoustical technique for locating the objects like submarine or icebergs etc by transmitting a high frequency sound pulse and receiving it after reflection from that object.

5.     What is piezo electric eect ? Deine the converse piezoelectric effect also.

When pressure or mechanical orce is applied along mechanical axis with respect to the Optic axis then equal and opposite charges are produced along the electrical axis with respect to the Optic axis. This eect is called Piezo electric effect.

6.     When potential difference or e.m.f is applied along the electrical axis with respect to the Optic axis of the piezoelectric crystal, the crystal starts vibrating along the optic axis mechanical axis of the crystal with respect to the Optic axis. This effect is called Converse or Inverse Piezo electric effect.

The principle of the Piezo Electric oscillator is Converse Piezo electric effect or Inverse Piezo-electric effect. When potential difference or e.m.f is applied along the electrical axis with respect to the Optic axis of the piezoelectric crystal, the crystal starts vibrating along the optic axis mechanical axis of the crystal with respect to the Optic axis. This effect is called Converse or Inverse Piezo-electric effect.

7.     Mention the application of Ultrasonics.

a.     Ultrasonic are used in cutting, drilling welding, soldering etc.

b.     They are used to increase the sensitivity of the colour in photographs by dispersion of the dye in the emulsion.

c.      They are used to remove air bubbles in the liquid metals and convert them into used metals.

d.     Low frequency ultrasonic waves are used in sorting paper fibers from the paper pulp.

8.     What is meant by Cavitation?

Cavitation is the process of creation and collapse of the bubbles, due to the principle o negative local pressure created inside the bubble.

9.     What are the medical applications of the Ultrasonic in industries?

a.     Diagnostic application: Ultrasonic waves are used for detecting tumours and other defects in Human body.

b.     Surgical Application: Ultrasonic waves are used to remove the kidney stones and brain tumours without the loss of blood.

c.      Disease treatment: Ultrasonic waves are used to treat diseases like neuralgic and rheumatic pains etc.

10.                         What is the principle of inding the velocity of ultrasonic using acoustical grating?

Principle: When the ultrasonic waves are passed through a liquid like kerosene contained in a tank, due to variation in pressure, the liquid acts as acoustical grating, It produces orders of spectrum due to diffraction. Using diffraction condition we can find the velocity of Ultrasonic.

i.e.,