Waves- 2 Practice Questions - DPP for NEET

 Page 1


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A police car moving at 22 m/s, chases a motorcylist. The
police man sounds his horn at 176 Hz, while both of them
move towards a stationary siren of frequency 165 Hz.
Calculate the speed of the motorcycle, if it is given that he
does not observes any beats
 Police Car Motorcycle
Stationary siren
(165 Hz)
22 m/s
(176 Hz)
(a) 33 m/s (b) 22 m/s (c) Zero (d) 11 m/s
Q.2 A closed organ pipe of length L and an open organ pipe
contain gases of densities 
1
r and 
2
r respectively. The
compressibility of gases are equal in both the pipes. Both
the pipes are vibrating in their first overtone with same
frequency. The length of the open organ pipe is
(a)
3
L
(b)
4
3
L
(c)
1
2
4
3
L r
r
(d)
2
1
4
3
L r
r
Q.3 Two whistles 
A
and 
B
produces notes of frequencies 660
Hz and 596 Hz respectively . There is a listener at the mid-
point of the line joining them. Now the whistle B and the
listener start moving with speed 30 m/s away from the
whistle A. If speed of sound be 330 m/s, how many beats
will be heard by the listener
(a)2 (b)4 (c)6 (d)8
Page 2


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A police car moving at 22 m/s, chases a motorcylist. The
police man sounds his horn at 176 Hz, while both of them
move towards a stationary siren of frequency 165 Hz.
Calculate the speed of the motorcycle, if it is given that he
does not observes any beats
 Police Car Motorcycle
Stationary siren
(165 Hz)
22 m/s
(176 Hz)
(a) 33 m/s (b) 22 m/s (c) Zero (d) 11 m/s
Q.2 A closed organ pipe of length L and an open organ pipe
contain gases of densities 
1
r and 
2
r respectively. The
compressibility of gases are equal in both the pipes. Both
the pipes are vibrating in their first overtone with same
frequency. The length of the open organ pipe is
(a)
3
L
(b)
4
3
L
(c)
1
2
4
3
L r
r
(d)
2
1
4
3
L r
r
Q.3 Two whistles 
A
and 
B
produces notes of frequencies 660
Hz and 596 Hz respectively . There is a listener at the mid-
point of the line joining them. Now the whistle B and the
listener start moving with speed 30 m/s away from the
whistle A. If speed of sound be 330 m/s, how many beats
will be heard by the listener
(a)2 (b)4 (c)6 (d)8
2
DPP/ P 30
Q.4 An open organ pipe is in resonance in its 2
nd
 harmonic
with tuning fork of frequency f
1
. Now, it is closed at one
end. If the frequency of the tuning fork is increased slowly
from f
1 
then again a resonance is obtained with a frequency
f
2
. If in this case the pipe vibrates n
th
 hamonics then
(a)
21
3
3,
4
n ff == (b)
21
5
3,
4
n ff ==
(c)
21
5
5,
4
n ff == (d)
21
3
5,
4
n ff ==
Q.5 The source producing sound and an observer both are
moving along the direction of propagation of sound waves.
If the respective velocities of sound, source and an
observer are v, v
s
 and v
0
, then the apparent frequency heard
by the observer will be (n = frequency of sound)
(a)
0
0
() nvv
vv
+
-
(b)
0
()
s
nvv
vv
-
-
(c)
0
()
s
nvv
vv
-
+
(d)
0
()
s
nvv
vv
+
+
Q.6 A whistle sends out 256 waves in a second. If the whistle
approaches the observer with velocity 1/3 of the velocity
of sound in air, the number of waves per second the
observer will receive
(a) 384 (b) 192 (c) 300 (d) 200
Q.7 A source of sound emitting a note of frequency 200 Hz
moves towards an observer with a velocity v equal to the
velocity of sound. If the observer also moves away from
the source with the same velocity v, the apparent frequency
heard by the observer is
(a) 50 Hz (b) 100 Hz (c) 150 Hz (d) 200 Hz
Q.8 The speed of sound in air at a given temperature is 350 m/
s. An engine blows whistle at a frequency of 1200 cps. It is
approaching the observer with velocity 50 m/s. The apparent
frequency in cps heard by the observer will be
(a) 600 (b) 1050 (c) 1400 (d) 2400
Q.9 A source of sound of frequency n is moving towards a
stationary observer with a speed S. If the speed of sound in
air is V and the frequency heard by the observer is 
1
n ,the
value of 
1
/ nn is
(a) (V + S)/V (b) V/ (V + S)
(c) (V – S)/V (d) V/ (V – S)
Q.10An observer is moving away from source of sound of
frequency 100 Hz. His speed is 33 m/s. If speed of sound
is 330 m/s, then the observed frequency is
(a) 90 Hz (b) 100 Hz (c) 91 Hz (d) 110 Hz
Q.11 A whistle giving out 450 Hz approaches a stationary
observer at a speed of 33 m/s. The frequency heard by the
observer in Hz is
(a) 409 (b) 429 (c) 517 (d) 500
Q.12 Two sirens situated one kilometre apart are producing sound
of frequency 330 Hz. An observer starts moving from one
siren to the other with a speed of 2 m/s. If the speed of
sound be 330 m/s, what will be the beat frequency heard
by the observer
(a)8 (b)4 (c)6 (d)1
Q.13 A small source of sound moves on a circle as shown in the
figure and an observer is standing on O. Let 
12
, nn and 
3
n be
the frequencies heard when the source is at , AB and
C
respectively . Then
(a)
1 23
n nn >>
(b)
2 31
n nn ><
(c)
1 23
n nn =>
O (d)
2 13
n nn >>
Q.14 A person carrying a whistle emitting continuously a note
of 272 Hz is running towards a reflecting surface with a
speed of 18 km/hour. The speed of sound in air is 345ms
–
1
. The number of beats heard by him is
(a)4 (b)6 (c)8 (d)3
Q.15 A source of sound of frequency 256 Hz is moving rapidly
towards a wall with a velocity of 5m/s. The speed of sound
is 330 m/s. If the observer is between the wall and the
source, then the beats heard per second will be
(a) 7.8 Hz (b) 7.7 Hz
(c) 3.9 Hz (d) Zero
Q.16 The harmonics which are present in a pipe open at one end
are
(a) odd harmonics
(b) even harmonics
(c) even as well as odd harmonics
(d) None of these
Page 3


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A police car moving at 22 m/s, chases a motorcylist. The
police man sounds his horn at 176 Hz, while both of them
move towards a stationary siren of frequency 165 Hz.
Calculate the speed of the motorcycle, if it is given that he
does not observes any beats
 Police Car Motorcycle
Stationary siren
(165 Hz)
22 m/s
(176 Hz)
(a) 33 m/s (b) 22 m/s (c) Zero (d) 11 m/s
Q.2 A closed organ pipe of length L and an open organ pipe
contain gases of densities 
1
r and 
2
r respectively. The
compressibility of gases are equal in both the pipes. Both
the pipes are vibrating in their first overtone with same
frequency. The length of the open organ pipe is
(a)
3
L
(b)
4
3
L
(c)
1
2
4
3
L r
r
(d)
2
1
4
3
L r
r
Q.3 Two whistles 
A
and 
B
produces notes of frequencies 660
Hz and 596 Hz respectively . There is a listener at the mid-
point of the line joining them. Now the whistle B and the
listener start moving with speed 30 m/s away from the
whistle A. If speed of sound be 330 m/s, how many beats
will be heard by the listener
(a)2 (b)4 (c)6 (d)8
2
DPP/ P 30
Q.4 An open organ pipe is in resonance in its 2
nd
 harmonic
with tuning fork of frequency f
1
. Now, it is closed at one
end. If the frequency of the tuning fork is increased slowly
from f
1 
then again a resonance is obtained with a frequency
f
2
. If in this case the pipe vibrates n
th
 hamonics then
(a)
21
3
3,
4
n ff == (b)
21
5
3,
4
n ff ==
(c)
21
5
5,
4
n ff == (d)
21
3
5,
4
n ff ==
Q.5 The source producing sound and an observer both are
moving along the direction of propagation of sound waves.
If the respective velocities of sound, source and an
observer are v, v
s
 and v
0
, then the apparent frequency heard
by the observer will be (n = frequency of sound)
(a)
0
0
() nvv
vv
+
-
(b)
0
()
s
nvv
vv
-
-
(c)
0
()
s
nvv
vv
-
+
(d)
0
()
s
nvv
vv
+
+
Q.6 A whistle sends out 256 waves in a second. If the whistle
approaches the observer with velocity 1/3 of the velocity
of sound in air, the number of waves per second the
observer will receive
(a) 384 (b) 192 (c) 300 (d) 200
Q.7 A source of sound emitting a note of frequency 200 Hz
moves towards an observer with a velocity v equal to the
velocity of sound. If the observer also moves away from
the source with the same velocity v, the apparent frequency
heard by the observer is
(a) 50 Hz (b) 100 Hz (c) 150 Hz (d) 200 Hz
Q.8 The speed of sound in air at a given temperature is 350 m/
s. An engine blows whistle at a frequency of 1200 cps. It is
approaching the observer with velocity 50 m/s. The apparent
frequency in cps heard by the observer will be
(a) 600 (b) 1050 (c) 1400 (d) 2400
Q.9 A source of sound of frequency n is moving towards a
stationary observer with a speed S. If the speed of sound in
air is V and the frequency heard by the observer is 
1
n ,the
value of 
1
/ nn is
(a) (V + S)/V (b) V/ (V + S)
(c) (V – S)/V (d) V/ (V – S)
Q.10An observer is moving away from source of sound of
frequency 100 Hz. His speed is 33 m/s. If speed of sound
is 330 m/s, then the observed frequency is
(a) 90 Hz (b) 100 Hz (c) 91 Hz (d) 110 Hz
Q.11 A whistle giving out 450 Hz approaches a stationary
observer at a speed of 33 m/s. The frequency heard by the
observer in Hz is
(a) 409 (b) 429 (c) 517 (d) 500
Q.12 Two sirens situated one kilometre apart are producing sound
of frequency 330 Hz. An observer starts moving from one
siren to the other with a speed of 2 m/s. If the speed of
sound be 330 m/s, what will be the beat frequency heard
by the observer
(a)8 (b)4 (c)6 (d)1
Q.13 A small source of sound moves on a circle as shown in the
figure and an observer is standing on O. Let 
12
, nn and 
3
n be
the frequencies heard when the source is at , AB and
C
respectively . Then
(a)
1 23
n nn >>
(b)
2 31
n nn ><
(c)
1 23
n nn =>
O (d)
2 13
n nn >>
Q.14 A person carrying a whistle emitting continuously a note
of 272 Hz is running towards a reflecting surface with a
speed of 18 km/hour. The speed of sound in air is 345ms
–
1
. The number of beats heard by him is
(a)4 (b)6 (c)8 (d)3
Q.15 A source of sound of frequency 256 Hz is moving rapidly
towards a wall with a velocity of 5m/s. The speed of sound
is 330 m/s. If the observer is between the wall and the
source, then the beats heard per second will be
(a) 7.8 Hz (b) 7.7 Hz
(c) 3.9 Hz (d) Zero
Q.16 The harmonics which are present in a pipe open at one end
are
(a) odd harmonics
(b) even harmonics
(c) even as well as odd harmonics
(d) None of these
DPP/ P 30
3
Q.17A source of sound placed at the open end of a resonance
column sends an acoustic wave of pressure amplitude P
0
inside the tube. If the atmospheric pressure is P
A
, then the
ratio of maximum and minimum pressure at the closed end
of the tube will be
(a)
0
0
()
()
A
A
PP
PP
+
-
(b)
0
0
( 2)
( 2)
A
A
PP
PP
+
-
(c)
A
A
P
P
(d)
0
0
1
2
1
2
A
A
PP
PP
æö
+
ç÷
èø
æö
-
ç÷
èø
Q.18 The frequency of fundamental tone in an open organ pipe
of length 0.48 m is 320 Hz. Speed of sound is 320 m/sec.
Frequency of fundamental tone in closed organ pipe will
be
(a) 153.8 Hz (b) 160.0  Hz
(c) 320.0  Hz (d) 143.2  Hz
Q.19 A standing wave having 3 nodes and 2 antinodes is formed
between two atoms having a distance 1.21Å between them.
The wavelength of the standing wave is
(a) 1.21 Å (b) 2.42 Å (c) 6.05 Å (d) 3.63 Å
Q.20A string on a musical instrument is 50 cm long and its
fundamental frequency is 270 Hz. If the desired frequency
of 1000 Hz, is to be produced, the required length of the
string is
(a) 13.5 cm (b) 2.7 cm (c) 5.4 cm (d) 10.3 cm
Q.21 The loudness and the pitch of a sound depends on
(a) intensity and velocity
(b) frequency and velocity
(c) intensity and frequency
(d) frequency and number of harmonics
Q.22 If in an experiment for determination of velocity of sound
by resonance tube method using a tuning fork of 512 Hz,
first resonance was observed at 30.7 cm and second was
obtainded at 63.2 cm, then maximum possible error in
velocity of sound is (consider actual speed of sound in air
is 332 m/s)
(a) 204 cm/sec (b) 110 cm/sec
(c) 58 cm/sec (d) 80 cm/sec
DIRECTIONS (Q.23-Q.25) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.23You are given four tuning forks, the lowest frequency of
the fork is 300Hz. By striking two tuning forks at a time
any of 1, 2, 3, 5, 7 & 8 Hz beat frequencies are heard. The
possible frequencies of the other three forks –
(1) 301, 302 & 307 (2) 301, 303 & 308
(3) 300, 304 & 307 (4) 305, 307 & 308
Q.24 Doppler shift in frequency depends upon
(1) the frequency of the wave produced
(2) the velocity of the source
(3) the velocity of the observer
(4) distance from the source to the listener
Q.25 The ( ,) xy coordinates of the corners of a square plate are
(0, 0), (L, 0), (L, L) and (0, L). The edges of the plate are
clamped and transverse standing waves are set up in it. If
( ,) uxy denotes the displacement of the plate at the point
( ,) xy at some instant of time, the possible expression(s)
for u is (are) (a = positive constant)
(1) sin sin
xy
a
LL
pp
(2)
2
sin sin
xy
a
LL
pp
(3) cos cos
22
xy
a
LL
pp
(4)
2
cos cos
xy
a
LL
pp
DIRECTIONS (Q.26-Q.27) : Read the passage given below
and answer the questions that follows :
A plate was cut from a quartz crystal and is used to control the
frequency of an oscillating electrical circuit. Longitudinal
standing waves are set up in the plate with displacement antinodes
at opposite faces. The fundamental frequency of vibration is
given by the equation f
0
 = 
4
2.87 10
s
´
. Here s is thickness of
 the plate and density of quartz is 2658.76 kg/m
3
.
Page 4


DIRECTIONS (Q.1-Q.22) : There are 22 multiple choice
questions. Each question has 4 choices (a), (b), (c) and (d), out
of which ONLY ONE choice is correct.
Q.1 A police car moving at 22 m/s, chases a motorcylist. The
police man sounds his horn at 176 Hz, while both of them
move towards a stationary siren of frequency 165 Hz.
Calculate the speed of the motorcycle, if it is given that he
does not observes any beats
 Police Car Motorcycle
Stationary siren
(165 Hz)
22 m/s
(176 Hz)
(a) 33 m/s (b) 22 m/s (c) Zero (d) 11 m/s
Q.2 A closed organ pipe of length L and an open organ pipe
contain gases of densities 
1
r and 
2
r respectively. The
compressibility of gases are equal in both the pipes. Both
the pipes are vibrating in their first overtone with same
frequency. The length of the open organ pipe is
(a)
3
L
(b)
4
3
L
(c)
1
2
4
3
L r
r
(d)
2
1
4
3
L r
r
Q.3 Two whistles 
A
and 
B
produces notes of frequencies 660
Hz and 596 Hz respectively . There is a listener at the mid-
point of the line joining them. Now the whistle B and the
listener start moving with speed 30 m/s away from the
whistle A. If speed of sound be 330 m/s, how many beats
will be heard by the listener
(a)2 (b)4 (c)6 (d)8
2
DPP/ P 30
Q.4 An open organ pipe is in resonance in its 2
nd
 harmonic
with tuning fork of frequency f
1
. Now, it is closed at one
end. If the frequency of the tuning fork is increased slowly
from f
1 
then again a resonance is obtained with a frequency
f
2
. If in this case the pipe vibrates n
th
 hamonics then
(a)
21
3
3,
4
n ff == (b)
21
5
3,
4
n ff ==
(c)
21
5
5,
4
n ff == (d)
21
3
5,
4
n ff ==
Q.5 The source producing sound and an observer both are
moving along the direction of propagation of sound waves.
If the respective velocities of sound, source and an
observer are v, v
s
 and v
0
, then the apparent frequency heard
by the observer will be (n = frequency of sound)
(a)
0
0
() nvv
vv
+
-
(b)
0
()
s
nvv
vv
-
-
(c)
0
()
s
nvv
vv
-
+
(d)
0
()
s
nvv
vv
+
+
Q.6 A whistle sends out 256 waves in a second. If the whistle
approaches the observer with velocity 1/3 of the velocity
of sound in air, the number of waves per second the
observer will receive
(a) 384 (b) 192 (c) 300 (d) 200
Q.7 A source of sound emitting a note of frequency 200 Hz
moves towards an observer with a velocity v equal to the
velocity of sound. If the observer also moves away from
the source with the same velocity v, the apparent frequency
heard by the observer is
(a) 50 Hz (b) 100 Hz (c) 150 Hz (d) 200 Hz
Q.8 The speed of sound in air at a given temperature is 350 m/
s. An engine blows whistle at a frequency of 1200 cps. It is
approaching the observer with velocity 50 m/s. The apparent
frequency in cps heard by the observer will be
(a) 600 (b) 1050 (c) 1400 (d) 2400
Q.9 A source of sound of frequency n is moving towards a
stationary observer with a speed S. If the speed of sound in
air is V and the frequency heard by the observer is 
1
n ,the
value of 
1
/ nn is
(a) (V + S)/V (b) V/ (V + S)
(c) (V – S)/V (d) V/ (V – S)
Q.10An observer is moving away from source of sound of
frequency 100 Hz. His speed is 33 m/s. If speed of sound
is 330 m/s, then the observed frequency is
(a) 90 Hz (b) 100 Hz (c) 91 Hz (d) 110 Hz
Q.11 A whistle giving out 450 Hz approaches a stationary
observer at a speed of 33 m/s. The frequency heard by the
observer in Hz is
(a) 409 (b) 429 (c) 517 (d) 500
Q.12 Two sirens situated one kilometre apart are producing sound
of frequency 330 Hz. An observer starts moving from one
siren to the other with a speed of 2 m/s. If the speed of
sound be 330 m/s, what will be the beat frequency heard
by the observer
(a)8 (b)4 (c)6 (d)1
Q.13 A small source of sound moves on a circle as shown in the
figure and an observer is standing on O. Let 
12
, nn and 
3
n be
the frequencies heard when the source is at , AB and
C
respectively . Then
(a)
1 23
n nn >>
(b)
2 31
n nn ><
(c)
1 23
n nn =>
O (d)
2 13
n nn >>
Q.14 A person carrying a whistle emitting continuously a note
of 272 Hz is running towards a reflecting surface with a
speed of 18 km/hour. The speed of sound in air is 345ms
–
1
. The number of beats heard by him is
(a)4 (b)6 (c)8 (d)3
Q.15 A source of sound of frequency 256 Hz is moving rapidly
towards a wall with a velocity of 5m/s. The speed of sound
is 330 m/s. If the observer is between the wall and the
source, then the beats heard per second will be
(a) 7.8 Hz (b) 7.7 Hz
(c) 3.9 Hz (d) Zero
Q.16 The harmonics which are present in a pipe open at one end
are
(a) odd harmonics
(b) even harmonics
(c) even as well as odd harmonics
(d) None of these
DPP/ P 30
3
Q.17A source of sound placed at the open end of a resonance
column sends an acoustic wave of pressure amplitude P
0
inside the tube. If the atmospheric pressure is P
A
, then the
ratio of maximum and minimum pressure at the closed end
of the tube will be
(a)
0
0
()
()
A
A
PP
PP
+
-
(b)
0
0
( 2)
( 2)
A
A
PP
PP
+
-
(c)
A
A
P
P
(d)
0
0
1
2
1
2
A
A
PP
PP
æö
+
ç÷
èø
æö
-
ç÷
èø
Q.18 The frequency of fundamental tone in an open organ pipe
of length 0.48 m is 320 Hz. Speed of sound is 320 m/sec.
Frequency of fundamental tone in closed organ pipe will
be
(a) 153.8 Hz (b) 160.0  Hz
(c) 320.0  Hz (d) 143.2  Hz
Q.19 A standing wave having 3 nodes and 2 antinodes is formed
between two atoms having a distance 1.21Å between them.
The wavelength of the standing wave is
(a) 1.21 Å (b) 2.42 Å (c) 6.05 Å (d) 3.63 Å
Q.20A string on a musical instrument is 50 cm long and its
fundamental frequency is 270 Hz. If the desired frequency
of 1000 Hz, is to be produced, the required length of the
string is
(a) 13.5 cm (b) 2.7 cm (c) 5.4 cm (d) 10.3 cm
Q.21 The loudness and the pitch of a sound depends on
(a) intensity and velocity
(b) frequency and velocity
(c) intensity and frequency
(d) frequency and number of harmonics
Q.22 If in an experiment for determination of velocity of sound
by resonance tube method using a tuning fork of 512 Hz,
first resonance was observed at 30.7 cm and second was
obtainded at 63.2 cm, then maximum possible error in
velocity of sound is (consider actual speed of sound in air
is 332 m/s)
(a) 204 cm/sec (b) 110 cm/sec
(c) 58 cm/sec (d) 80 cm/sec
DIRECTIONS (Q.23-Q.25) : In the following questions,
more than one of the answers  given are correct. Select the
correct answers and mark it according to the following
codes:
Codes :
(a) 1, 2 and 3 are correct (b) 1 and 2 are correct
(c) 2 and 4 are correct (d) 1 and 3 are correct
Q.23You are given four tuning forks, the lowest frequency of
the fork is 300Hz. By striking two tuning forks at a time
any of 1, 2, 3, 5, 7 & 8 Hz beat frequencies are heard. The
possible frequencies of the other three forks –
(1) 301, 302 & 307 (2) 301, 303 & 308
(3) 300, 304 & 307 (4) 305, 307 & 308
Q.24 Doppler shift in frequency depends upon
(1) the frequency of the wave produced
(2) the velocity of the source
(3) the velocity of the observer
(4) distance from the source to the listener
Q.25 The ( ,) xy coordinates of the corners of a square plate are
(0, 0), (L, 0), (L, L) and (0, L). The edges of the plate are
clamped and transverse standing waves are set up in it. If
( ,) uxy denotes the displacement of the plate at the point
( ,) xy at some instant of time, the possible expression(s)
for u is (are) (a = positive constant)
(1) sin sin
xy
a
LL
pp
(2)
2
sin sin
xy
a
LL
pp
(3) cos cos
22
xy
a
LL
pp
(4)
2
cos cos
xy
a
LL
pp
DIRECTIONS (Q.26-Q.27) : Read the passage given below
and answer the questions that follows :
A plate was cut from a quartz crystal and is used to control the
frequency of an oscillating electrical circuit. Longitudinal
standing waves are set up in the plate with displacement antinodes
at opposite faces. The fundamental frequency of vibration is
given by the equation f
0
 = 
4
2.87 10
s
´
. Here s is thickness of
 the plate and density of quartz is 2658.76 kg/m
3
.
4
DPP/ P 30
Q.26 Young’s modulus of elasticity for quartz is –
(a) 7 × 10
11
 N/m
2
(b) 8.76 × 10
12
 N/m
2
(c) 2 × 10
12
 N/m
2
(d) Information insufficient
Q.27If the quartz plate is vibrating in 3
rd
 harmonic while
measuring the frequency of 1.2 × 10
6
 Hz, then the thickness
of the plateis
(a) 71.75cm (b) 7.175 cm
(c) 6.02 cm (d) 0.07 cm
DIRECTIONS (Q.28-Q.30) : Each of these questions contains
two statements: Statement-1 (Assertion) and Statement-2
(Reason). Each of these questions has four alternative choices,
only one of which is the correct answer. You have to select the
correct choice.
Q.28 Statement-1 : Beats cannot be produced by light sources.
Statement-2: Light sources have constant phase
difference.
Q.29 Statement-1 : In the case of a stationary wave, a person
hear a loud sound at the nodes as compared to the antinodes.
Statement-2 : In a stationary wave all the particles of the
medium vibrate in phase.
Q.30 Statement-1 : Velocity of particles, while crossing mean
position (in stationary waves) varies from maximum at
antinodes to zero at nodes.
Statement-2: Amplitude of vibration at antinodes is
maximum and at nodes, the amplitude is zero, and all
particles between two successive nodes cross the mean
position together.