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AL-MC-Doppler effect / p.1
1.
(88-I-27)
A. (1), (2) and (3)
A moving train sounds a whistle of frequency
B. (1) and (2) only
500 Hz. The apparent frequency heard by an
C. (2) and (3) only
observer standing close to the railroad is 462 Hz. If
D. (1) only
the speed of sound in air is
E. (3) only
300 ms 1 , the train
is moving at a speed of
4.
(93-I-26)
A hydrogen source in a laboratory emits a line
A.
B.
C.
D.
E.
2.
-1
spectrum with one of the lines having wavelength
-1
656.3 nm. For a star receding from the earth at a
-1
speed of 200 km/s, what would be the wavelength
-1
of the corresponding line from the star observed on
-1
the earth? (Velocity of light = 3  10 ms
23 ms away from the observer.
23 ms towards the observer.
25 ms away from the observer.
25 ms towards the observer.
8
28 ms away from the observer.
(89-I-24)
A.
655.5 nm
A stationary radar source emits waves of frequency
B.
655.9 nm
f , and wavelength  which are reflected from
C.
656.7 nm
an object moving towards the source at a speed u.
D.
657.1 nm
The reflected waves reaching a receiver standing
E.
657.5 nm
1
)
near to the radar source will have an apparent
wavelength of
5.
(94-IIA-19)
An ambulance, sounding its siren to produce a note
A.
B.
C.
D.
E.
3.
  2u / f .
 u/ f .
.
 u/ f.
  2u / f .
of 800 Hz, approaches a stationary pedestrian P at a
steady speed of 40 ms-1. Calculate the frequency of
the sound heard by P.
(Speed of sound in air = 340 ms-1)
A.
706 Hz
B.
716 Hz
Sound waves of frequency f are emitted by a
C.
800 Hz
source S. When S is moved with speed u (relative
D.
894 Hz
to the ground) towards a stationary observer O, a
E.
907 Hz
(90-I-24)
rise in pitch of  f is detected. Which of the
following statements is/are correct?
(1)
The speed of sound waves relative to the
observer is unaffected by the motion of S.
(2)
If both S and O move in the same direction
with speed u, no rise in pitch will be
detected.
(3)
If S is at rest with O moving towards it at
speed u, the rise in pitch will also be  f .
AL-MC-Doppler effect / p.2
6.
(95-IIA-18)
8.
An aircraft flies near the earth’s surface over a
A boy sitting at the rim of a rotating
stationary observer on a windless day. The
merry-go-round blows a whistle continuously with
frequency of the notes from the engine received by
frequency fo. An observer on the ground hears the
the observer is 300 Hz when approaching, and
sound of the whistle. Which of the graphs below
becomes 150 Hz when leaving. Assume the speed
gives the possible variation of the observed
-1
7.
(01-IIA-18)
of sound in air to be 336 ms . The speed of the
frequency f of the sound in a period of revolution
aircraft is
T?
A.
56 ms-1
B.
84 ms-1
C.
112 ms-1
D.
168 ms-1
E.
224 ms-1
(99-IIA-14)
On a straight road, a car and an ambulance move
with uniform speeds u 1 and u 2 respectively (with
u 2 > u 1 ) in the same direction. Initially the
ambulance is behind the car and it overtakes the car
after some time. The siren on the ambulance
continuously emits a sound of a certain frequency.
What is the ratio of the wavelength of sound
9.
(02-IIB-18)
received by an observer in the car before the
When source emitting sound waves of a fixed
ambulance overtakes to that after the ambulance
frequency moves towards a stationary observer in
overtakes?
air, the pitch of the sound heard by the observer is
(Given : velocity of sound in air = v)
different from the that when the source is at rest.
This is due a change in the
A.
B.
C.
D.
E.
v  u2
v  u2
(i)
v  u2
v  u2
(ii)
Speed of the sound in air.
(ii)
Wavelength of sound in air.
u 2  u1
u 2  u1
number of waves emitted per second from
the source.
A.
(1) only
v  u 2  u1
v  u 2  u1
B.
(3) only
C.
(1) and (2) only
v  u 2  u1
v  u 2  u1
D.
(2) and (3) only
AL-MC-Doppler effect / p.3
10.
(02-IIB-19)
The spectra produced by element X, one on earth
and the other on a distant star, are compared.
spectrum from element X on earth:
Spectrum from element X on the distant star:
What is the most probable reason for the difference
in the spectra readings?
A.
The universe is expanding
B.
The star is approaching the earth
C.
The star is receding from the earth
D.
The star is spinning about its axis