C7 B PEDAGOGY OF PHYSICAL SCIENCE

2.  Sound board
 Basically curved surfaces
 Used in auditoria and halls
 Board is placed at focus to the concave
surface
 To improve the quality of sound

3.  Hearing aid
 One end is wider , other is narrow
 Sound from wide end reflected by its wall
into narrow
 Helps in concentrating the sound

4.  Horn shaped device
 To address small gathering
 Concentrated by multiple reflections from
walls of tube

5.  Explained by austrian mathematician and
physicist
 1803 to 1853
 Definition
 “ when ever there is a relative motion
between a source and a listener the
frequency of the sound heard by the listener
is different from the original frequency of
sound emitted by the source known as
doppler effect “

6.  Let s be the source
 L be the listener
 Vs and VL be the velocities
Source s listener L

7.  Both source and listener move
 They move towards each other
 n’ = ( v + vL/v – vs ) n
 Both source and listener mve
 They move away from each other
 n’ = ( v - vL/v + vs ) n
 Both source and listener move
 They move one behind the other
 Source follows the listener
 n’ = ( v - vL/v – vs ) n

8.  Both source and listener move
 The move one behind the other
 Listener follows the source
 n’ = ( v + vL/v + vs ) n
 Source at rest
 Listener moves towards the source
 n’ = ( v + vL/v ) n
 Source at rest
 Listener moves away from the source
 n’ = ( v - vL/v ) n

9.  Listener at rest
 Source moves towards the listener
 n’ = ( v /v – vs ) n
 Listener at rest
 Source moves away from the listener
 n’ = ( v /v + vs ) n
 Suppose medium is moving with velocity W
 Then direction of propagation of sound is
v+w
 The direction opposite to propagation of
sound is v-w

10.  When source and listener
 Both are at rest
 Move in a way that distance between them
remains constant
 Moving in mutually perpendicular directions
 Source at center of the circle along which
the listener is moving

11.  To measure the speed of the atomobile
 Tracking the satellite
 Radar
 sonar

12. Thank you