2.  What
have you observed with the sound of
these vehicles as they pass by at a certain
speed?
 What
explanation can offer to account for
this observation?
 What
are the key variable involved?

4.  The
apparent change in the frequency of a
source of wave due to the motion of the
source and/or the observer
 Developed
 The
by Christian Doppler in 1842
difference of the true frequency and the
apparent frequency is called the Doppler
Shift

5. The following symbols will be used in the
definitions:
f
is the true frequency
 f’
is the apparent frequency
v
is the velocity of the sound (air)
 vs
is the velocity of the source
 vo is the velocity of the observer
λ
is the true wavelength
 λ’ is the apparent wavelength

6. f
’ = [ ( v ± vo ) / v ] f
 ( + ) means the observer is moving towards
the source
 ( - ) means the observer is moving away
from the source

7. f
’ = [ v / ( v ± vs ) ] f
 ( + ) means the source is moving away from
the observer
 ( - ) means the source is moving towards the
observer

8. f
’ = [ ( v ± vo ) / ( v ± vs ) ] f
 NOTE: please refer to case 1 and case 2
and analyze the situation of the observer
and the source respectively.

9.  When
a wave source moves toward a
receiver, does the receiver encounter an
increase in wave frequency, wave speed ,or
both?
 Does
the Doppler Effect occur for only some
types of waves or all types of waves?

10.  named
after Austrian physicist and
philosopher Ernst Mach
 Used to describe speed of objects that are
travelling close to, or above the speed of
sound.
 The ratio of the speed of the object and the
speed of sound in the medium.
M
= speed of object / speed of sound

11.  this
is heard as a sonic boom when an
airplane passes over; this is the result of the
compilation of sound waves generated by a
source that moves at equal or greater
velocity than the sound it creates

12. 1.
An ambulance traveling at 20. m/s sounds its siren
at a frequency of 256Hz. What apparent frequency
will you hear if the ambulance is:
( assume air temperature to be at 25°C )
a. approaching you?
b. moving away from you?
2. A car traveling at 30. m/s sounds its horn as it
overtakes and pass another car traveling at 20. m/s
in the same direction. If the frequency of the horn is
500. Hz, what is the frequency heard by the driver in
the slower car:
a.) before
b.) after the car has passed?
Assume sound speed to be at 350. m/s.