The correct option is (c).
Explanation
Ultrasound refers to sound waves with frequencies higher than the upper audible limit of human hearing (typically above 20 kHz). Due to their high frequency, short wavelength, and high energy, these waves are extensively used in industrial and medical applications for cleaning, detection, and machining.
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Statement 1 is Correct:
Ultrasound is widely used for cleaning objects with parts that are difficult to reach, such as spiral tubes, odd-shaped parts, and electronic components. The objects are placed in a cleaning solution, and ultrasonic waves are passed through the liquid. The high-frequency vibrations create microscopic bubbles (cavitation) that implode, detaching dust, grease, and dirt from the surfaces. -
Statement 2 is Incorrect:
Ultrasound is a primary method for Non-Destructive Testing (NDT) to detect internal cracks, voids, or flaws in metal blocks. When ultrasonic waves pass through a metal block, they travel in straight lines but reflect back if they encounter a crack or flaw, even if it is not visible from the outside. Detectors monitor these reflections to identify defects. -
Statement 3 is Correct:
Ultrasonic machining (USM) is an industrial process used to drill holes or cut complex shapes in hard and brittle materials, including steel, glass, and ceramics. In this process, a tool vibrates at ultrasonic frequencies and drives abrasive particles against the workpiece to erode material and create the desired hole or shape.
Key Takeaway:
Ultrasound in industry is primarily utilized for precision cleaning of complex components, non-destructive testing (flaw detection) in metals, and machining (drilling/cutting) hard materials.