DC Pandey Solutions: Sound Waves

DC Pandey Solutions: Sound Waves | DC Pandey Solutions for NEET Physics PDF Download

``` Page 1

Introductory Exercise 16.1
Q1: Calculate the bulk modulus of air from the following data for a sound
wave of wavelength 35 cm travelling in air. The pressure at a point varies
between (10 ± 14) Pa and the particles of the air vibrate in SHM of
amplitude 5.5 × 10 m.
Sol:
Q2: Find the minimum and maximum wavelengths of sound in water that is
in the audible range for an average human ear. Speed of sound in water is
1450 m/s.
Sol: (a) For minimum wavelength n = 20 KHz
Q3: A typical loud sound wave with a frequency of 1 kHz has a pressure
amplitude of about 10 Pa (a) At t = 0, the pressure is a maximum at some
point x . What is the displacement at that point at t = 0?
5
-6
1
Page 2

Introductory Exercise 16.1
Q1: Calculate the bulk modulus of air from the following data for a sound
wave of wavelength 35 cm travelling in air. The pressure at a point varies
between (10 ± 14) Pa and the particles of the air vibrate in SHM of
amplitude 5.5 × 10 m.
Sol:
Q2: Find the minimum and maximum wavelengths of sound in water that is
in the audible range for an average human ear. Speed of sound in water is
1450 m/s.
Sol: (a) For minimum wavelength n = 20 KHz
Q3: A typical loud sound wave with a frequency of 1 kHz has a pressure
amplitude of about 10 Pa (a) At t = 0, the pressure is a maximum at some
point x . What is the displacement at that point at t = 0?
5
-6
1
(b) What is the maximum value of the displacement at any time and place ?
Take the density of air to be 1.29 kg/m and speed of sound in air is 340
m/s.
Sol: (a) Displacement is zero when pressure is maximum.
Q4:  The pressure variation in a sound wave in air is given by
?P = 12 sin(8.18x - 2700t +p/4) N/m
Find the displacement amplitude. Density of air = 1.29 kg/m .
Sol: In the above problem, we have found that
Now substituting the value, we have

Introductory Exercise 16.2
Q1: Calculate the temperature at which the velocity of sound in air is
double its velocity at 0°C.
Sol: Speed of velocity in air is, v ? vT
3
2
3
Page 3

Introductory Exercise 16.1
Q1: Calculate the bulk modulus of air from the following data for a sound
wave of wavelength 35 cm travelling in air. The pressure at a point varies
between (10 ± 14) Pa and the particles of the air vibrate in SHM of
amplitude 5.5 × 10 m.
Sol:
Q2: Find the minimum and maximum wavelengths of sound in water that is
in the audible range for an average human ear. Speed of sound in water is
1450 m/s.
Sol: (a) For minimum wavelength n = 20 KHz
Q3: A typical loud sound wave with a frequency of 1 kHz has a pressure
amplitude of about 10 Pa (a) At t = 0, the pressure is a maximum at some
point x . What is the displacement at that point at t = 0?
5
-6
1
(b) What is the maximum value of the displacement at any time and place ?
Take the density of air to be 1.29 kg/m and speed of sound in air is 340
m/s.
Sol: (a) Displacement is zero when pressure is maximum.
Q4:  The pressure variation in a sound wave in air is given by
?P = 12 sin(8.18x - 2700t +p/4) N/m
Find the displacement amplitude. Density of air = 1.29 kg/m .
Sol: In the above problem, we have found that
Now substituting the value, we have

Introductory Exercise 16.2
Q1: Calculate the temperature at which the velocity of sound in air is
double its velocity at 0°C.
Sol: Speed of velocity in air is, v ? vT
3
2
3
Q2: Calculate the difference in the speeds of sound in air at -3°C, 60 cm
pressure of mercury and 30°C, 75 cm pressure of mercury. The speed of
sound in air at 0°C is 332 m/s.
Sol: v ? vT
?
= 330.17 m/s
= 349.77 m/s
The difference in these two speeds is approximately 20 m/s.
Q3: In a liquid wit h density 900 kg/m , longitudinal waves with frequency
250 Hz are found to have wavelength 8.0 m. Calculate the bulk modulus of
the liquid.
Sol:
? B = ? (f?)
= (900) (250 × 8) = 3.6 × 10 N/m
Q4: Calculate the speed of sound in oxygen at 273 K.
Sol:
= 315 m/s
Introductory Exercise 16.3
Q1: A sound wave in air has a frequency of 300 Hz and a displacement
amplitude of 6.0 × 10 -3 mm. For this sound wave calculate the
(a) pressure amplitude
(b) intensity
(c) sound intensity level (in dB)
3
2
2 9 2
Page 4

Introductory Exercise 16.1
Q1: Calculate the bulk modulus of air from the following data for a sound
wave of wavelength 35 cm travelling in air. The pressure at a point varies
between (10 ± 14) Pa and the particles of the air vibrate in SHM of
amplitude 5.5 × 10 m.
Sol:
Q2: Find the minimum and maximum wavelengths of sound in water that is
in the audible range for an average human ear. Speed of sound in water is
1450 m/s.
Sol: (a) For minimum wavelength n = 20 KHz
Q3: A typical loud sound wave with a frequency of 1 kHz has a pressure
amplitude of about 10 Pa (a) At t = 0, the pressure is a maximum at some
point x . What is the displacement at that point at t = 0?
5
-6
1
(b) What is the maximum value of the displacement at any time and place ?
Take the density of air to be 1.29 kg/m and speed of sound in air is 340
m/s.
Sol: (a) Displacement is zero when pressure is maximum.
Q4:  The pressure variation in a sound wave in air is given by
?P = 12 sin(8.18x - 2700t +p/4) N/m
Find the displacement amplitude. Density of air = 1.29 kg/m .
Sol: In the above problem, we have found that
Now substituting the value, we have

Introductory Exercise 16.2
Q1: Calculate the temperature at which the velocity of sound in air is
double its velocity at 0°C.
Sol: Speed of velocity in air is, v ? vT
3
2
3
Q2: Calculate the difference in the speeds of sound in air at -3°C, 60 cm
pressure of mercury and 30°C, 75 cm pressure of mercury. The speed of
sound in air at 0°C is 332 m/s.
Sol: v ? vT
?
= 330.17 m/s
= 349.77 m/s
The difference in these two speeds is approximately 20 m/s.
Q3: In a liquid wit h density 900 kg/m , longitudinal waves with frequency
250 Hz are found to have wavelength 8.0 m. Calculate the bulk modulus of
the liquid.
Sol:
? B = ? (f?)
= (900) (250 × 8) = 3.6 × 10 N/m
Q4: Calculate the speed of sound in oxygen at 273 K.
Sol:
= 315 m/s
Introductory Exercise 16.3
Q1: A sound wave in air has a frequency of 300 Hz and a displacement
amplitude of 6.0 × 10 -3 mm. For this sound wave calculate the
(a) pressure amplitude
(b) intensity
(c) sound intensity level (in dB)
3
2
2 9 2
Speed of sound = 344 m/s and density of air = 1.2 kg/m .
Sol: (a)
= 4.67 Pa
(b)
(c)
Q2: Most people interpret a 9.0 dB increase in sound intensity level as a
doubling in loudness. By what factor must the sound intensity be increased
to double the loudness?Sol:
Given L - L =9 dB
Solving the equation we get,
Q3: A baby's mouth is 30 cm from her father's ear and 3.0 m from her
mother's ear. What is the, difference between the sound intensity levels
heard by the father and by the mother.
Sol:
?
3
2 1
Page 5

Introductory Exercise 16.1
Q1: Calculate the bulk modulus of air from the following data for a sound
wave of wavelength 35 cm travelling in air. The pressure at a point varies
between (10 ± 14) Pa and the particles of the air vibrate in SHM of
amplitude 5.5 × 10 m.
Sol:
Q2: Find the minimum and maximum wavelengths of sound in water that is
in the audible range for an average human ear. Speed of sound in water is
1450 m/s.
Sol: (a) For minimum wavelength n = 20 KHz
Q3: A typical loud sound wave with a frequency of 1 kHz has a pressure
amplitude of about 10 Pa (a) At t = 0, the pressure is a maximum at some
point x . What is the displacement at that point at t = 0?
5
-6
1
(b) What is the maximum value of the displacement at any time and place ?
Take the density of air to be 1.29 kg/m and speed of sound in air is 340
m/s.
Sol: (a) Displacement is zero when pressure is maximum.
Q4:  The pressure variation in a sound wave in air is given by
?P = 12 sin(8.18x - 2700t +p/4) N/m
Find the displacement amplitude. Density of air = 1.29 kg/m .
Sol: In the above problem, we have found that
Now substituting the value, we have

Introductory Exercise 16.2
Q1: Calculate the temperature at which the velocity of sound in air is
double its velocity at 0°C.
Sol: Speed of velocity in air is, v ? vT
3
2
3
Q2: Calculate the difference in the speeds of sound in air at -3°C, 60 cm
pressure of mercury and 30°C, 75 cm pressure of mercury. The speed of
sound in air at 0°C is 332 m/s.
Sol: v ? vT
?
= 330.17 m/s
= 349.77 m/s
The difference in these two speeds is approximately 20 m/s.
Q3: In a liquid wit h density 900 kg/m , longitudinal waves with frequency
250 Hz are found to have wavelength 8.0 m. Calculate the bulk modulus of
the liquid.
Sol:
? B = ? (f?)
= (900) (250 × 8) = 3.6 × 10 N/m
Q4: Calculate the speed of sound in oxygen at 273 K.
Sol:
= 315 m/s
Introductory Exercise 16.3
Q1: A sound wave in air has a frequency of 300 Hz and a displacement
amplitude of 6.0 × 10 -3 mm. For this sound wave calculate the
(a) pressure amplitude
(b) intensity
(c) sound intensity level (in dB)
3
2
2 9 2
Speed of sound = 344 m/s and density of air = 1.2 kg/m .
Sol: (a)
= 4.67 Pa
(b)
(c)
Q2: Most people interpret a 9.0 dB increase in sound intensity level as a
doubling in loudness. By what factor must the sound intensity be increased
to double the loudness?Sol:
Given L - L =9 dB
Solving the equation we get,
Q3: A baby's mouth is 30 cm from her father's ear and 3.0 m from her
mother's ear. What is the, difference between the sound intensity levels
heard by the father and by the mother.
Sol:
?
3
2 1
Now
Substituting

We get, L - L - 20 dB
Q4: The faintest sound that can be heard has a pressure amplitude of about
2 × 10 N/m and the loudest that can be heard without pain has a
pressure amplitude of about 28 N/m . Determine in each case
(a) the intensity of the sound both in W/m and in dB and
(b) the amplitude of the oscillations if the frequency is 500 Hz. Assume an
air density of 1.29 kg/m and a velocity of sound is 345 m/s.
Sol:
For finest sound,
= - 3.48 dB
Same formulae can be applied for loudest sound.
?
For finest sound,
= 1.43 × 10 m
x1 2
-5 2
2
2
3
-11
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FAQs on DC Pandey Solutions: Sound Waves - DC Pandey Solutions for NEET Physics

 1. What are sound waves?
Ans. Sound waves are a type of mechanical waves that transfer energy through vibrations in a medium, such as air, water, or solids. These vibrations create compressions and rarefactions, resulting in the perception of sound.
 2. How does sound travel through different mediums?
Ans. Sound waves travel differently through different mediums. In solids, sound waves propagate faster due to the close arrangement of particles. In liquids, sound waves travel slower compared to solids. In gases, such as air, sound waves travel the slowest due to the larger gaps between particles.
 3. What determines the pitch and frequency of sound waves?
Ans. The pitch and frequency of sound waves are determined by the frequency of the vibrating source. Higher frequency vibrations produce higher-pitched sounds, while lower frequency vibrations produce lower-pitched sounds. The unit for frequency is hertz (Hz).
 4. How does the amplitude of sound waves affect the volume?
Ans. The amplitude of sound waves determines the volume or loudness of the sound. Higher amplitude waves create louder sounds, while lower amplitude waves create softer sounds. The amplitude is related to the energy of the sound wave, with higher amplitudes carrying more energy.
 5. How does the speed of sound change with temperature?
Ans. The speed of sound increases with an increase in temperature. This is because higher temperatures lead to greater molecular motion and faster propagation of sound waves. Conversely, a decrease in temperature results in a decrease in the speed of sound.

DC Pandey Solutions for NEET Physics

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