Railway Science (Physics-Sound)

Infrasonic sounds - The sounds of frequency less than 20 Hz are called infrasonic sounds. Example - Sound produced by earthquakes, thunder, volcanoes. The human Ear cannot hear this sound but elephants and whales can hear this. Ultrasonic sounds - The sound of frequency more than 20,000Hz are called ultrasonics. Example - The audible range of dogs, cats, moths and mice extends into ultrasound frequencies. They can hear very high frequencies that humans cannot.

Sound waves are longitudinal waves that travel through a medium like air or water and the speed of sound in air is 343 m/sec. In any medium, the speed of sound is independent of frequency. The speed of sound is maximum in solids and minimum in gases. The unit of loudness of sound is decibel (dB). Among all metals, speed of sound is maximum in Aluminium.

It is used to find out the depth of the sea and the position of the objects located in the water. Intensity refers to the magnitude, strength, of a given physical quantity at a given location in space. Ranging is a technique that measures distance or slant range from the observer to a target. Vibration is a rapid linear motion of a particle or an elastic medium about an equilibrium position. is a rapid to and fro motion of the object.

Microphones are a type of transducer - a device that converts energy from one form to another. A speaker converts electrical energy into sound energy. Electric generator - Mechanical energy into electrical energy. Cell or Battery - Chemical energy into electrical energy. Electric Iron - Electrical energy into heat energy. Solar cells - Light energy into electrical energy. Electric Bulb - Electrical energy into light energy. Gas stove - Chemical energy into heat energy. Solar water heater - Light energy into heat energy.

Of the three mediums (Gas, Liquid, and Solid) sound waves travel the slowest through gases, faster through liquids, and fastest through solids. Temperature also affects the speed of sound. Molecules at higher temperatures have more energy and can vibrate faster and allow sound waves to travel more quickly.

Echo - A sound that is repeated as it is sent back off a surface such as the wall of a tunnel. Reflection - The act of reflecting, as in coming back to light or heat. Refraction - The change in direction of a wave passing from one medium to another or from a gradual change in the medium.

(low-frequency sound) - Other animals can make noise as loud as (in decibel): Sperm Whales (233 decibel), Mantis Shrimp (200), Blue whales (188), Greater Bulldog Bat (140), Howler Monkey (140), Elephant Seal (126), African Cicadas (120), North American Bullfrog (119). Animals With the best Hearing (Frequency Range): Greater Wax Moth (Up to 30000 Hz), Dolphin (2 - 200000 Hz), Bat (9000 - 200000 Hz), Rat (250 - 80000 Hz), Cat (55 - 79000 Hz), Dog (67 - 45000 Hz), Elephant (12 - 12000 Hz), Horse (14 - 2500 Hz).

Speed of sound (decibel - dB) - Distance traveled per unit time by a sound wave as it propagates through an elastic medium. it is 331m/s. Speed of Sound in Medium - Solid > Liquids > Gases. Speed of light - 3×10⁸ m/s.

SONAR (Sound Navigation and Ranging) is used by submarines, Ships, and other vessels to navigate, detect objects, and communicate, fish finding, depth sounding, mapping of the sea bottom, Doppler navigation. It is also used by scientists to study the ocean and its inhabitants. An acoustic projector produces a sound wave that propagates outward and is reflected back by the target object. RADAR (Radio Detection And Ranging).

The Pitch of a sound depends on its frequency. The faster the vibration of the source, the higher is the frequency and the higher is the pitch. Objects of different sizes and conditions vibrate at different frequencies to produce sounds of different pitch. Amplitude - The Measure of the height of the wave. It corresponds to the loudness of the sound.