Test: Sound Waves - UPSC MCQ

Applications of Ultrasonic Waves are: sending signals, for measuring the depth of sea, for cleaning cloths, aeroplanes, machinery parts of clocks, for removing lamp-shoot from the chimney of factories, in sterilizing of liquid and in Ultrasonography.

The speed of sound increases with the increase of temperature of the medium. The speed of sound in air increases by 0.61 m/s when the temperature is increased by1⁰C.

The phenomenon that explains why sound is heard at longer distances at night than during the day is due to refraction. At night, the air above the ground is warmer, causing the sound waves to bend towards the earth. This is known as a temperature inversion. Therefore, the correct answer is:

D: Refraction

Sound or Audible waves are sensitive to human ear and are generated by the vibrating bodies like tuning fork, vocal cords etc. Infrasonic waves are produced by sources of bigger size such as earth quakes, volcanic eruptions, ocean waves etc. Human ear cannot detect Ultrasonic waves. But dog, cat, bat etc can detect these waves. Bat not only detect but also produce ultrasonic waves.

Intensity of any sound at any point in space is the amount of energy passing normally per unit area held around that point per unit time. S.I unit of intensity is watt/m². Therefore option C is correct

Sound waves are classified as longitudinal waves because they involve the oscillation of particles in the same direction as the wave propagates. In other words, the particles vibrate back and forth parallel to the direction of energy transfer. This is in contrast to transverse waves, where particles oscillate perpendicular to the direction of wave propagation.

In a sound wave, variations in pressure and density create areas of compression and rarefaction as the wave travels through a medium, such as air, water, or solids. The compression regions correspond to areas of higher pressure and density, while the rarefaction regions correspond to areas of lower pressure and density. The particles within the medium oscillate back and forth as the wave passes through, transmitting the energy of the sound.

This longitudinal motion of particles is responsible for the characteristic behavior of sound waves, such as the ability to propagate through different materials and the phenomenon of interference and resonance. It allows sound to travel through gases, liquids, and solids, albeit at different speeds depending on the medium.

The speed of Sound in Air (0⁰C) is 332 m/s and in Air (20⁰C) is 343 m/s.

When a motor boat in a sea travels faster than sound, then waves just like shock-waves are produced on the surface of water. These waves are called bow waves.

The sensation of a sound perceived in a ear is measured by another term called loudness which depends on intensity of sound and sensitiveness of the ear. Unit of loudness is bel. A practical unit of loudness is decibel (dB) which is 1/10th of bel. Another unit of loudness is phon.

Pitch is that characteristic of sound which distinguishes a sharp or shrill sound from a grave or dull sound. It depends upon frequency. Higher the frequency higher will be the pitch and shriller will be the sound and vice versa.