Science · X-Factor Notes
Sound Motion revision notes for UPPCS Prelims.
20 revision facts
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Sound Nature | Sound is a form of energy that produces a hearing sensation and travels in the form of waves. Sound waves are mechanical waves. Sound is transmitted through liquids and gases as longitudinal waves. | UPPCS (Pre) 1990, UPPCS (Pre) 2002, UPPCS (Pre) 2014, I.A.S. (Pre) 1995 |
| Medium Necessity | A medium (solid, liquid, or gas) is necessary for sound propagation. Sound waves cannot travel in vacuum. | UPPCS (Pre) 1990, UPPCS (Pre) 2014 |
| Speed in Media | The speed of sound is different for different types of medium. Speed is maximum in solids (metals) and minimum in gases. The velocity of sound in air is approximately 330 m/sec. | U.P. Lower (Spl) (Pre) 2008, UPPCS (Pre) 2018 |
| Speed Comparison | The speed order is typically VAir < VWater < VSteel. | U.P. U.D.A./L.D.A. (Spl) (Mains) 2010 |
| Medium Change Effect | When a sound wave goes from one medium to another, the quantity that remains unchanged is frequency. | UPPCS (Mains) 2008, UPPCS (Mains) 2010, UPPCS (Mains) 2017 |
| Astronaut Hearing | An astronaut cannot hear their companion on the surface of the Moon because there is no medium for sound propagation. | UPPCS (Mains) 2013 |
| Wavelength | In a sound wave (longitudinal), wavelength is the distance between two consecutive compressions or rarefactions. | |
| Wave Identity | When the same tone is played on a sitar and a flute, the sound produced can be distinguished from each other because of the difference in quality (timber) only. | I.A.S. (Pre) 1995 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Audible Range | The audible range (hearing range) for humans is 20 Hz to 20,000 Hz (or 20 kHz). | I.A.S. (Pre) 2000 |
| Ultrasonic Waves | Sound waves with frequency greater than 20,000 Hz. Used in clinical diagnosis like Sonography. | UPPCS (Mains) 2004, UPPCS(Pre) 2012 |
| Decibel (dB) | The commonly used unit to measure the intensity of sound in the atmosphere. | UPPCS (Mains) 2011, U.P. P.C.S. (Mains) 2017 |
| Loudness | Loudness is measured in terms of amplitude. | U.P. R.O./A.R.O. (Mains) 2017 |
| Noise Pollution Levels | Sound above 80 decibel is considered hazardous noise pollution. The optimum sound level for human beings (normal conversation) is 55 dB. WHO safe noise level for a city is 45 dB. | UPPCS(Pre) 2013, U.P. P.C.S. (Mains) 2008, UPPCS (Mains) 2010, U.P. R.O./A.R.O. (Mains) 2013 |
| Shrillness/Pitch | Determined by wavelength (shorter wavelength = higher frequency/more shrill). |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Echo | A sound caused by the reflection of sound waves. To hear a clear echo, a time interval of at least 0.1 second is needed, corresponding to a minimum distance of about 16.5 metre (about 17m) between the listener and reflector. | UPPCS (Mains) 2013 |
| Acoustic Design | The walls of a hall built for music concerts should absorb sound to prevent echoes/reverberation. | UPPCS (Mains) 2007 |
| Stethoscope | Works on the principle of multiple reflection of sound. | |
| Echolocation | Bats use ultrasonic waves and their returning echoes (echolocation) to navigate and find prey in the dark. | UPPCS (Mains) 2005 |
| Mach Number | It is the ratio of the speed of a body to the speed of sound in the surrounding medium. | |
| Ultrasonic Uses (General) | Ultrasonic waves are used to destroy insects, clean clothes, treat diseases, and control automatic doors, among other applications. | UPPCS (Mains) 2004 |
