Ch-12SOUND

PRODUCTION OF SOUND

• Sound is produced due to vibration of objects.

• Vibration is the to and fro motion of the objects.

PROPAGATION OF SOUND• When a vibrating object moves forward it pushes the

air in front of it forming a region of high pressurecalled compression.

• When the vibrating object moves backwards it createsa region of low pressure called rarefaction (R)

Sound needs a medium to travel

Characteristics of a sound wave

• The distance between two consecutivecompressions (C) or two consecutiverarefactions (R) is called the wavelength

• Frequency tells us how frequently an eventoccurs

• The time taken by two consecutivecompressions or rarefactions to cross a fixedpoint is called the time period of the wave

REFLECTION OF SOUND

•Sound bounces off a solid or a liquid like rubber ball bounces off a wall , this is called the reflection of sound.

•Laws of reflection

•Angle of incidence is equal to angle of reflection

•Incident ray, reflected ray and and normal at the point of incidence all lie on the same plane.

Uses of multiple reflection of sound.

•Megaphones or loudhailers, horns musical instruments suchas trumpets and shehanais, are all designed to end sound in aparticular direction without spreading it in all directions

•Stethoscope is a medical instrument used for listening tosounds produced within the body, chiefly in the heart or lungs.In stethoscopes the sound of the patient’s heartbeat reachesthe doctor’s ears by multiple reflection of sound

SONAR

• The acronym SONAR stands for Sound Navigation AndRanging. Sonar is a device that uses ultrasonic waves tomeasure the distance, direction and speed of underwaterobjects.

Human Ear • The outer ear is called pinna’. Itcollects the sound from thesurroundings. The collected soundpasses through the auditory canal.At the end of the auditory canalthere is a thin membrane called theear drum or tympanic membrane.

• The vibrations are amplified severaltimes by three bones (the hammer,anvil and stirrup) in the middle ear.

• The middle ear transmits theamplified pressure variationsreceived from the sound wave tothe inner ear. In the inner ear, thepressure variations are turned intoelectrical signals by the cochlea.These electrical signals are sent tothe brain via the auditory nerve, andthe brain interprets them as sound.

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