Physics - Wave Motion
Exam Duration: 45 Mins Total Questions : 30
A wire under tension vibrates with a fundamental frequency of 600Hz.If the length of the wire is doubled, then radius halved and the wire is made to vibrate under one-ninth of the tension.Then, fundamental frequency will be
- (a)
400Hz
- (b)
600Hz
- (c)
300Hz
- (d)
200Hz
When two waves of almost equal frequencies n1 and n2 are produced simultaneously, then the interval between successive maxima is
- (a)
\(1\over n_1-n_2\)
- (b)
\({1\over n_1}-{1\over n_2}\)
- (c)
\({1\over n_1}+{1\over n_2}\)
- (d)
\(1\over n_1+n_2\)
If the intensity of sound increases by a factor of 105, then increases in the intensity level is
- (a)
5dB
- (b)
10dB
- (c)
25dB
- (d)
50dB
The speed of sound in air is 340m/s.The speed with which a source of sound should move towards a stationary observer so that the apparent frequency becomes twice of the original is
- (a)
640 m/s
- (b)
340m/s
- (c)
170 m/s
- (d)
85 m/s
A traveling wave represented by y=Asin(\(\omega t-kx\)) is superimposed on another wave represented by y=Asin(\(\omega t+kx\)).The resultant is
- (a)
a standing wave having nodes at \(x=(n+{1\over2}){\lambda\over2},n=0,1,2\)
- (b)
a wave traveling along + x direction
- (c)
a wave traveling along - x direction
- (d)
a standing wave having nodes at \(x={n\lambda\over2};n=0,1,2\)
The displacement Y of a particle in a medium can be expressed as \(y=10^{-6}sin(100t+20x+{\pi\over4})\)m, where t is in second and x in metre.The speed of the waves is
- (a)
2000ms-1
- (b)
5ms-1
- (c)
20ms-1
- (d)
5\(\pi\)ms-1
Ultrasonic, infrasonic and audio waves travel through a medium with speed Vu ,Vi and Va respectively; then:
- (a)
Vu, Vi and Va are nearly equal
- (b)
Vu,≥ Vi ≥ Va
- (c)
Vu, ≤Vi ≤ Va
- (d)
Va≤ Vu and Vc=Vi
The equation of a sound wave is y = 0.0015 sin (62.4x + 316t). Find the wavelength of this wave:
- (a)
0.2 unit
- (b)
0.1 unit
- (c)
0.3 unit
- (d)
cannot be calculated
Velocity of sound waves in air is 330 m/s. For a particular sound in air, a path difference of 40 cm is equivalent to a phase difference of 1.61t. The frequency of the wave is:
- (a)
165 Hz
- (b)
150 Hz
- (c)
660 Hz
- (d)
330 Hz
The particles of a medium vibrate about their mean positions whenever a wave travels through that medium. The phase difference between the vibrations of two such particles:
- (a)
varies with time
- (b)
varies with distance separating them
- (c)
varies with time a~ well as distance
- (d)
is always zero
When a longitudinal wave propagates through a medium, the particles of the medium execute simple harmonic oscillations about their mean positions. These oscillations of a particle are characterised by an invariant:
- (a)
kinetic energy
- (b)
potential energy
- (c)
sum of kinetic energy and potential energy
- (d)
difference between kinetic energy and potential energy
- (a)
3.6
- (b)
3.6 x 10-6
- (c)
3.6 x 10-11
- (d)
3.6 x 10-4
When a sound wave of wavelength λ is propagating in a medium, the maximum velocity of the particle is equal to the wave velocity. The amplitude of wave is:
- (a)
λ
- (b)
\(\frac{\lambda}{2}\)
- (c)
\(\frac{\lambda}{2\pi}\)
- (d)
\(\frac{\lambda}{4\pi}\)
The ratio of velocity of sound in hydrogen and oxygen at STP is:
- (a)
16 : 1
- (b)
8 : 1
- (c)
4 : 1
- (d)
2 : 1
The velocities of sound in an ideal gas at temperatures T1 and T2 K are found to be V1 and V2 respectively. If the root mean square speeds of the Game gas at the same temperatures T1, and T2 are v1, and v2 respectively, then:
- (a)
v2 =v1(V2/V1)
- (b)
v2 =v1(V1/V2)
- (c)
\({ v }_{ 2 }={ v }_{ 1 }\sqrt { { V }_{ 2 }/{ V }_{ 1 } } \)
- (d)
\({ v }_{ 2 }={ v }_{ 1 }\sqrt { { V }_{ 1 }/{ V }_{ 2 } } \)
A man stands between two parallel cliffs (not in middle). When he claps his hands, he hears two echoes one after 1 second and the other after 2 seconds. If the velocity of sound in air is 330 m s -1, the width of the valley is
- (a)
330 m
- (b)
495 m
- (c)
660 m
- (d)
990 m
An echo repeats 2 syllables. If the speed of sound is 330 m s -1, then the distance of the reflecting surface is:
- (a)
16.5 m
- (b)
33.0 m
- (c)
66.0 m
- (d)
99.0 m
In a plane progressive harmonic wave particle speed is always less than the wave speed if:
- (a)
amplitude of wave<λ/2π
- (b)
amplitude of wave>λ/2π
- (c)
amplitude of wave<λ
- (d)
amplitude of wave>λ/π
A tuning fork is set into vibrations and then it is held with its stem resting on a table. How will duration of its vibrations be affected?
- (a)
It will vibrate for same duration
- (b)
It will vibrate for a longer duration
- (c)
It will vibrate for a shorter duration
- (d)
The duration will increase or decrease depending upon the dimensions of the table
If Vm is the velocity of sound in moist air, Vd is the velocity of sound in dry air, under identical conditions of pressure and temperature:
- (a)
vm > vd
- (b)
v m < vd
- (c)
v m = vd
- (d)
v mvd =1
Velocity of sound in a gaseous medium is 330 m s -1 . If the pressure is increased by 4 times without change in temperature, the velocity of sound in the gas is:
- (a)
330ms-1
- (b)
660ms-1
- (c)
156ms-1
- (d)
990ms-1
- (e)
1320ms-1
A window whose area is 2 m2 opens on a street where street noises result in an intensity level at the window of 60 dB. How much acoustic power enters the window via sound waves and if an acoustic absorber is fitted at the window, how much energy from street noise will it collect in five hours?
- (a)
3μW,2x 10-3 J
- (b)
2μW,36x 10-3 J
- (c)
36μW,2x 10-3 J
- (d)
2μW,3.6x 10-3 J
An auditorium has volume 105m3 and surface area of absorption 2 x 104 m2. Its average absorption coefficient is 0.2. The reverberation time of the auditorium (in seconds) is:
- (a)
6.5
- (b)
5.5
- (c)
4.25
- (d)
3.25
A plane progressive wave is given by: y=2cos 6.284(330t-x). What is the period of the wave?
- (a)
\(\frac{1}{330}s\)
- (b)
2πx330 s
- (c)
(2πx330)-1 s
- (d)
\(\frac{6.284}{330}s\)
A string is hanging from a rigid support. A transverse pulse is excited at its free end. The speed at which the pulse travels a distance xis proportional to:
- (a)
x
- (b)
\(\frac{1}{x}\)
- (c)
\(\frac{1}{\sqrt{x}}\)
- (d)
x2
- (e)
\(\sqrt{x}\)
Two points are located at a distance of 10 m and 15 m from the source of oscillation. The period of oscillation is 0.05 see and the velocity of the wave is 300 m/sec. What is the phase difference between the oscillations of two points?
- (a)
π rad
- (b)
π/6 rad
- (c)
π/3 rad
- (d)
2π/3 rad
The speed of sound in oxygen (O2) at a certain temperature is 460 ms-1. The speed of sound in helium (He) at the same temperature will be: (assume both gases to be ideal)
- (a)
1420 ms-1
- (b)
500 ms-1
- (c)
650 ms-1
- (d)
330 ms-1