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Questions and Answers
What physical property of a sound wave primarily determines its loudness?
What physical property of a sound wave primarily determines its loudness?
The pitch of a sound wave is most closely related to which of the following?
The pitch of a sound wave is most closely related to which of the following?
What phenomenon occurs when a driving force matches an object's natural frequency?
What phenomenon occurs when a driving force matches an object's natural frequency?
Which of the following best describes a spherical wave?
Which of the following best describes a spherical wave?
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In a graphical representation of spherical waves, what do the circular arcs represent?
In a graphical representation of spherical waves, what do the circular arcs represent?
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What happens to the wavelength of a sound wave in a spherical wave representation, as the distance from the sources increases?
What happens to the wavelength of a sound wave in a spherical wave representation, as the distance from the sources increases?
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What do the radial lines that point outward from the source in a spherical wave diagram represent?
What do the radial lines that point outward from the source in a spherical wave diagram represent?
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As a spherical sound wave expands from its source, what happens to its surface area, given 'r' is the radius?
As a spherical sound wave expands from its source, what happens to its surface area, given 'r' is the radius?
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What is the relationship between energy propagation and direction in a spherical wave?
What is the relationship between energy propagation and direction in a spherical wave?
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Intensity of a wave is defined as the rate at which energy flows divided by which parameter?
Intensity of a wave is defined as the rate at which energy flows divided by which parameter?
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At a distance of $r_1$ from a sound source, given the average intensity is $I_1$, what can be said about the average power of the sound source at distance $r_2$?
At a distance of $r_1$ from a sound source, given the average intensity is $I_1$, what can be said about the average power of the sound source at distance $r_2$?
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What is the approximate intensity of the faintest sound detectable by the human ear at 1000 Hz?
What is the approximate intensity of the faintest sound detectable by the human ear at 1000 Hz?
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What is the approximate intensity of the loudest sound the human ear can tolerate?
What is the approximate intensity of the loudest sound the human ear can tolerate?
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If a sound has a level of 50 dB at a distance of 10 km, which of the following is required to calculate the sound intensity in W/m²?
If a sound has a level of 50 dB at a distance of 10 km, which of the following is required to calculate the sound intensity in W/m²?
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Given a sound with a calculated intensity of 0.00401 $W/m^2$, and a reference intensity $I_0$ of $1 x 10^{-12} W/m^2$, what is the approximate sound intensity level in dB?
Given a sound with a calculated intensity of 0.00401 $W/m^2$, and a reference intensity $I_0$ of $1 x 10^{-12} W/m^2$, what is the approximate sound intensity level in dB?
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Which of these correctly uses the information to calculate the average power of a horn, given that when measured, a sound intensity level of 50 dB is heard 10km away and the sound power is represented by P?
Which of these correctly uses the information to calculate the average power of a horn, given that when measured, a sound intensity level of 50 dB is heard 10km away and the sound power is represented by P?
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Study Notes
Introduction to General Physics II - Sound II
- Course: M 6.2.2
- Instructor: Dr Orlaith Brennan
- Topics covered include loudness, pitch, resonance, plane waves, spherical waves, sound energy and power, reference intensity, and decibel calculations.
Learning Outcomes
- Students will be able to explain loudness and pitch.
- Students will be able to define resonance.
- Students will be able to describe the difference between plane and spherical waves.
- Students will be able to apply energy and power concepts and equations to sound waves.
- Students will be able to recall the reference intensity.
- Students will be able to calculate sound intensity levels in decibels (dB).
Loudness
- Loudness of a sound wave is determined by the amplitude of the sound wave.
- A greater amplitude results in greater loudness.
- Loudness is related to the energy entering the ear per second.
Pitch
- Pitch of a note depends on the frequency of the sound wave.
- Higher frequency = higher pitch
- Lower frequency = lower pitch
Resonance
- Natural frequency is the frequency at which an object tends to vibrate.
- Resonance occurs when the frequency of a force applied to a body is the same as, or very near to, its natural frequency.
- A body vibrating under resonance experiences large amplitude.
- Example: Tacoma Narrows Bridge collapse.
Human Body Resonance Frequencies
- Different body parts have specific resonance frequencies.
- These frequency ranges are relevant to particular body parts.
- Examples are given for various anatomical parts, e.g., eyeball, head, shoulder girdle, lower arm, chest wall, arm, hand, abdominal mass, and spinal column, with their specific ranges in Hz.
Spherical Waves
- Vibration at a point source initiates a sound wave.
- Wave fronts spread out uniformly in all directions from the point source.
- Wave travels as a 3D sphere.
- Spherical waves are graphically represented with circular arcs (wave fronts).
- The distance between adjacent wave fronts is the wavelength (λ).
- The lines pointing outwards from the source and perpendicular to the arc are called rays.
Plane Waves
- Far from the source, wave fronts are parallel planes.
- A segment of a wave is approximately a plane wave.
Spherical Waves (Surface Area)
- Surface area of a sound wave increases with distance from the source.
- The surface area ∝ r2 (4πr2)
Energy and Intensity of Sound Waves
- Intensity (I) is the amount of energy flowing through a certain area in a specific amount of time.
- I = ΔE / (Δt * A) where ΔE is the energy change, Δt is the time, and A is the area.
- P is the sound power passing through an area (A).
- Intensity also related to I = P / (4πr2), which is dependent on power and distance from the source.
Power and Intensity of Sound Waves for spherical surfaces
- Average power is the same through any spherical surface centered at the source, at the same radius.
Intensity of Sound Waves
- Faintest sound the human ear detects at 1000 Hz has an intensity of approximately 1 x 10-12 W/m2 (threshold of hearing).
- Loudest sounds tolerate by the human ear has an intensity of ~1 W/m2 (threshold of pain).
- Relative intensity of a sound is called intensity level (β) or decibel level.
- β = 10 log10(I/Io), Io is the reference intensity (1 x 10-12 W/m2), I is the intensity.
Common Sounds and Sound Levels
- Examples of common sounds and their respective sound levels (dB) are given.
Power/Energy Problem
- Examples of calculation of power and calculating intensity level given various scenarios (like a train horn).
- Equations I = P / (4πr2), and β = 10 log(I / I0) are used repeatedly.
Important equations
- Sphere Surface Area = 4πr2
- β = 10log(I/I0)
- I = P/A (or) P = I x Area
- I= P/(4πr^2)
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Description
This quiz covers key concepts in sound, including loudness, pitch, resonance, and the differences between plane and spherical waves. Students will explore sound energy, power, reference intensity, and decibel calculations, applying equations to real-life scenarios. Test your understanding of these fundamental principles of sound physics!
