1. L7 - 09.3.2016 Sound Waves _____________________________________________________________________ Sound :Form of energy emitted by a vibrating source transmitted through material medium produces a sensation of hearing Various properties will be discussed along with applications;  Nature of sound waves  Range of frequencies  Piezoelectric effect  Cluster of Quartz crystal  Measuring wind speeds  Metrological instruments; Anemometer, hygrometer, barometer,  Bolometer, tachometer, dynamometer  Lithotripter etc.

2. Sound : Form of energy emitted by a vibrating source transmitted through material medium produces a sensation of hearing Mandatory Requirement: Mandatory Requirement: Material medium for transmission Wave motion Source produces disturbance of the medium - particles of the Medium vibrate about their mean positions - motion is handed Over from particle to particle without any transport of medium – A kind of push-pull mechanism - creating compressions and rarefactions (Longitudinal)

3. Nature of Sound Waves Velocity of Sound (in air = 332 m/sec) affected by; i) Density of gas --- Sound waves will travel 4-times faster in H 2 than on O 2 ii) Humidity ; velocity  humidity (travels faster on a rainy day !) iii) Pressure ; Independent of pressure as long as Temperature is constant __________ iv)Temperature ; velocity   temperature Velocity increases 61 cm/s for every 1 0 rise in temperature !

4. Range of frequencies Frequency range : Grown-up male 100-250 Hz Children/women200-450 Hz House Fly350 Hz Honey Bee440 Hz Mosquito500 – 600 Hz Bats30 – 50 KHz Dolphin  100 KHz Pigeon0.5 Hz (Incredible) Frequency < 20 Hz → Infrasonic Frequency > 20 KHz → Ultrasonic Audio-frequency range 20 – 20K Hertz (Audible to human ear

5. Piezoelectric effect Electric charges are developed on opposite faces on a quartz crystal When a pair of faces opposite and perpendicular to them are subjected to pressure or compression The signs of charges change when faces are subjected to Tension instead of compression. Electric charge developed  the degree of pressure or tension applied. Conversely If the electric field is applied across the second pair of faces, Compression or Tension depending upon the field direction occurs across the first pair of faces. Quartz crystal : Piezo-electric crystal J. Curie and P. Curie - 1880

6. Quartz : the second most abundant mineral in the Earth's crust. It is a silicate material. Made up of a continuous framework of SiO 4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO 2. Many different varieties of quartz, several of these are semi-precious gemstones Cluster of quartz crystals

7. Metrological (Study of Atmosphere) Instruments Anemometers Two classes: (velocity anemometers and Pressure anemometers) Pressure Anemometer : Displacement of a hanging plate by wind speed Rotation Anemometer : consists of a wind mill or a propeller (Standard in weather stations) Hotwire Anemometer : Amount of current required to keep a wire hot at a constant temperature as wind blows Acoustic Anemometer : Wind effects on the sound signal Anemometer : Measures Wind speed Barometer:Air pressure Hygrometer:Humidity Thermometer:Temperature

8. Barometer Most important metrological instrument for measuring atmospheric pressure Mercury Barometer:Fortin’s Barometer 1643 Evengelista Torricelli (Inventor) Used in Labs, and Major weather stations (1pascal =.01 millibar) Aneroid Barometer (1843) Functions without a liquid - evacuated metal box Used in homes, ships, weather stations etc.

9. Hygrometer An instrument used for measuring the moisture content in the atmosphere. It measures some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed. By calibration and calculation, these measured quantities can lead to a measurement of humidity. dew point Modern electronic hygrometers use the dew point (temperature of condensation) or changes in electrical capacitance or resistance to measure humidity differences.

10. Thermometer Measures temperature or a temperature gradient. Most common thermometers use mercury (freezes at -38.9 0 C, boils at 357 0 C) Alcohol, Toluene, Pentane etc. are now being preferred : freezing point at -200 0 C. pyrometer A pyrometer is a type of thermometer used to measure very high temperatures. For example in furnaces used in metallurgy. (>1300 0 C) Bolometer : A device for measuring the power of incident e. m. radiation in the (far IR and mm waves) via heating of a material with a temperature dependent electrical resistance

11. Dynamometer Device for measuring force, torque, or power output of rotating machinery Commonly used to test the horsepower developed by an electric motor or by engine of an automobile by measuring the braking force or torque applied to a rotating part and measuring the reduction in rotational speed. Two types: Absorption dynamometer and Transmission dynamometer

12. Tachometer Instrument that displays the speed of an engine in r.p.m Tachometer dial’s upper limit -- redline – shows the maximum speed at which the engine can be run An application of controlled shock waves (sound) Device which can be used for non-invasive surgery (such as removing kidney stones etc.) Lithotripter