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Practice Exercise¶

A rope of length \(5m\) is stretched to a tension of \(80N\). If its mass is \(1kg\), at what speed would a \(10Hz\) transverse wave travel down the string?
\(2m/s\)
\(5m/s\)
\(20m/s\)
\(50 m/s\)
Ans: \(20m/s\)
A transverse wave on a long horizontal rope with a wavelength of \(8m\) travels at \(2m/s\) At \(t=0\), a particular point on the rope has a vertical displacement of \(+A\), where \(A\) is the amplitude of the wave. At what time will the vertical displacement of this same point of the rope be \(-A\)?
\(t=1/8s\)
\(t=1/2s\)
\(t=4s\)
\(t=2s\)
Ans: \(t=2s\)
When two identical traveling waves are superimposed, the velocity of the resultant wave
Decreases
Increases
Remains unchanged
Becomes zero
Ans: Remains unchanged
In vibrating cord the points where the amplitude is maximum, are called
Antinodes
Nodes
Troughs
Crests
Ans: Antinodes
Echo is the phenomenon of
Interference of sound
Reflection of sound
Refraction of sound
None of these
Ans: Reflection of sound
A string, fixed at both ends, has a length of 6 m and supports a standing wave with a total of 4 nodes. If a transverse wave can travel at 40 m/s down the rope, what is the frequency of this standing wave?
\(6.7Hz\)
\(10.0Hz\)
\(13.3Hz\)
\(20.0Hz\)
Ans: \(10.0Hz\)
A stationary wave is set up in the air column of a closed pipe. At the closed end of the pipe
Always a node is formed
Always an antinode is formed
Neither node nor antinode is formed
Sometimes a node and sometimes an antinode is formed
Ans: Always a node is formed
A source of frequency \(f\) sends waves of wavelength \(\lambda\) traveling with speed \(v\) in some medium. If the frequency is changed from \(f\) to \(2f\), then the new wavelength and new speed are (respectively):
\(2\lambda\), \(v\)
\(\lambda/2\), \(v\)
\(\lambda\), \(2v\)
\(\lambda\), \(v/2\)
Ans: \(\lambda/2\), \(v\)
A tuning fork of frequency \(340Hz\) is sounded above a cylindrical tube \(1m\) high. Water is slowly poured into the tube. If the speed Of Sound \(340m/s\) at what levels of water in the tube will the sound of the fork be appreciably intensified?
25cm, 75cm
20cm, 80cm
15cm, 85cm
17cm, 83cm
Ans: 25cm, 75cm
What would a drummer do to make the sound of a drum given a note of lower pitch
Diffraction
Constructive interference
Destructive interference
Alternate constructive and destructive interference
Ans: Alternate constructive and destructive interference
Velocity of sound in vacuum is
\(332m/s\)
\(320m/s\)
Zero
\(224m/s\)
Ans: Zero
Increase in velocity of sound in the air for \(1^oC\) rise in temperature is
\(1.61m/s\)
\(61.0m/s\)
\(0.61m/s\)
\(2.00m/s\)
Ans: \(0.61m/s\)
Energy is not transferred by
Longitudinal wave
Transverse waves
Stationary waves
Electromagnetic waves
Ans: Stationary waves
On loading the prong of a tuning fork with wax, its frequency
Increases
Decreases
Remains unchanged
May increase or decrease
Ans: Decreases
The velocity of sound in air would become double than its velocity at \(0^oC\) at temperature
\(313^oC\)
\(586^oC\)
\(819^oC\)
\(1172^oC\)
Ans: \(819^oC\)
Fully constructive interference between two sinusoidal waves of the same frequency occurs only if they
Travel in opposite directions and are in phase
Travel in the same direction and are in phase
Travel in opposite directions and are 180° out of phase
Travel in the same direction and are 180° out of phase
Ans: Travel in the same direction and are in phase

A sound wave travels through a metal rod with wavelength \(\lambda\) and frequency \(f\) which of the following best describes the wave when it passes into the surrounding air?

#	Wavelength	Frequency
1	Less than \(\lambda\)	Equal to \(f\)
2	Less than \(\lambda\)	Less then \(f\)
3	Greater than \(\lambda\)	Equal to \(f\)
4	Greater than \(\lambda\)	Less than \(f\)

1

2

3

4

A string, clamped at its ends, vibrates in three segments. The string is \(100cm\) lung. wavelength is:
\(33.3cm\)
\(150cm\)
\(66.7cm\)
\(300cm\)
Ans: \(66.7cm\)
A tube closed at one end containing air, produces when excited the fundamental note of frequency \(512Hz\). If the tube at both ends, the fundamental frequency that can be excited is
1024Hz
512Hz
256Hz
128Hz
Ans: 1024Hz
A wave in soft string reflects from a hard steel rod. Its phase difference relative to incident wave will be
\(0^o\)
\(90^o\)
\(180^o\)
\(76^o\)
Ans: \(180^o\)
if the intensity of sound increases by a factor of \(10^5\) the increase in intensity level is
\(5dB\)
\(10dB\)
\(25dB\)
\(50dB\)
Ans: \(50dB\)
An observer is \(2m\) from a source of sound waves. By how much will the sound level decrease if the observer moves to a distance of \(20m\)?
\(1dB\)
\(2dB\)
\(10dB\)
\(20dB\)
Ans: \(20dB\)
An organ pipe with one end closed and the other open has length \(L\). Its fundamental frequency is proportional to
\(L\)
\(1/L\)
\(L^2\)
\(\sqrt{L}\)
Ans: \(1/L\)
To monitor blood flow through major arteries, ultrasonic waves of which frequencies are employed?
\(5\) to \(10Hz\)
\(5\) to \(10MHz\)
\(15\) to \(100MHz\)
None of these
Ans: \(5\) to \(10MHz\)
Which one is the correct relation for fundamental frequency of open and closed Pipe?
\(f_o=2f_c\)
\(f_c=2f_o\)
\(f_o=f_c\)
\(f_o=1/f_c\)
Ans: \(f_o=2f_c\)
In open organ pipe
Only even harmonics are present
Only odd harmonics are present
Both even and odd harmonics are present
Selected harmonics are present
Ans: Both even and odd harmonics are present
The minimum length of a tube, open at both ends, that resonates with a tuning fork of frequency \(350Hz\) is
\(0.25m\)
\(0.5m\)
\(1m\)
\(2m\)
Ans: \(1m\)
Progressive waves of frequency \(300 Hz\) are superimposed to produce a system of stationary waves in which adjacent nodes are \(1.5m\) apart. What is the speed of the progressive waves?
\(100 m/s\)
\(900 m/s\)
\(450 m/s\)
\(200 m/s\)
Ans: \(900 m/s\)
A source of sound moves towards a stationary observer with a speed one third that of sound. If the frequency of the sound from the source is \(100Hz\), the apparent frequency of the sound heard by the observer is
\(67 Hz\)
\(100 Hz\)
\(150 Hz\)
\(75 Hz\)
Ans: \(150 Hz\)
The source is moving towards a stationary observer then the pitch of the sound will
Sometimes increases and some times decreases
Remains constant
Decrease
Increase
Ans: Increase
A bat emits a \(40kHz\) "chirp" with a wavelength of \(8.75mm\) toward a tree and receives an echo \(0.4s\) later. How far is the bat from the tree?
35m
70m
105m
140m
Ans: 70m
Laplace found that the alternate compressions and rarefactions produced in sound waves follow
Isothermal law
Adiabatic law
Isochoric law
All of the above
Ans: Adiabatic law
For destructive interference of sound waves path difference between two interfering sounds should be:
\(n\lambda\)
\(\left(n+\frac{1}{2}\right)\lambda\)
Sometimes \(n\lambda\) sometimes \(\left(n+\frac{1}{2}\right)\lambda\)
None of these
Ans: \(\left(n+\frac{1}{2}\right)\lambda\)
When water waves pass from deep water into shallow water how do the frequency, waves length and speed changes

# Frequency Wavelength Speed

1 Increase Decrease No change

2 No change Decrease Decrease

3 No change Increase Increases

1
2
3
None of these
Ans: 2
The beats frequency sensible for a human ear is
\(24Hz\)
\(10Hz\)
\(12Hz\)
\(16Hz\)
Ans: \(10Hz\)
The speed of stationary wave in a stretched string are independent of
Number of loops
Tension in the string
Point where string is plucked
Both 1 & 2
Ans: Both 1 & 2
The audible frequency range will be maximum for
Dog
Dolphin
Bat
Cat
Ans: Dolphin
A car is traveling at \(20m/s\) away from a stationary observer. If the car's horn emits a frequency of \(600Hz\), what frequency will the observer hear? (Use \(v=340m/s\) for the speed of sound)

\({34}/{36}\times600Hz\)
\({34}/{32}\times600Hz\)
\({36}/{34}\times600Hz\)
\({32}/{34}\times600Hz\)
Ans: \({34}/{36}\times600Hz\)

#	Frequency	Wavelength	Speed
1	Increase	Decrease	No change
2	No change	Decrease	Decrease
3	No change	Increase	Increases

Practice Exercise¶

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