Physics 2 - Lesson 1: Batteries and Sound

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Physics 2 Lesson 1

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Lesson 1: Batteries and Sound

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NOTE: Quizlet cards marked with CRB indicates that these flashcards cover the content found in the Content Review Books. Cards not marked with CRB cover the video playlist content. Enjoy! :)

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How does a Concentration Cell compare to a Galvanic Cell?

In a Concentration Cell, the electrodes consist of the same metal and the solutions consist of the same ions, except that the solutions have different concentrations. Hence the name: "Concentration" Cell.

In a Galvanic Cell, on the other hand, the electrodes and solutions are different on different sides of the cell.

<p>In a Concentration Cell, the electrodes consist of the same metal and the solutions consist of the same ions, except that the solutions have different concentrations. Hence the name: "Concentration" Cell.</p><p>In a Galvanic Cell, on the other hand, the electrodes and solutions are different on different sides of the cell.</p>

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Oxidation will occur on which side of a Concentration Cell? Reduction? Why?

Oxidation will occur on the less concentrated side, in order to produce more ions.

Reduction will occur on the more concentrated side in order to remove ions, creating an equilibrium between the concentrations on both sides.

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When determining the Cell Potential of a Concentration Cell, what equation can be used?

Ecell = E⁰cell - ((.0592/n)log(Q))

Q = Reaction Quotient

Ecell = Cell Potential

E⁰cell = Standard Cell Potential

n = Number of Electrons

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You have a Concentration Cell with Zn(s) as the metal. One side of the Cell has a concentration of ZnSO4 of 3.2⋅10^-4 M and the other side a concentration of 6.1⋅10^-3. What is the Cell Potential in this case?

(A) -.037

(B) -.37

(D) .037

Ecell = E⁰cell - ((.0592/n)log(Q))

Ecell = 0 - ((.0592/2)log(3.2⋅10^-4/6.1⋅10^-3))

Ecell = -

((3⋅10^-2)log(.5⋅10^-1))

Ecell = -(3⋅10^-2)(-1.5) (actual: -(.0296)(-1.28)

Ecell = approx. 4.5⋅10^-2 (actual: 0.037)

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The Cell Potential in the last problem was equal to .037. Does this mean the reaction is spontaneous, non-spontaneous, or in equilibrium?

If the Ecell is positive, it means the reaction is spontaneous, as is the case here.

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Why is the higher concentration in the denominator when calculating Q?

Q is calculated as products over reactants. In this case, we are going from high concentration (reactants) to low concentration (products), which means the higher concentration (reactants) will be on bottom when determining Q.

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Why is the Standard Cell Potential 0 in a Concentration Cell?

The same half-reaction is occurring in opposite directions on either side, having the same E⁰cell. For instance, for Zn2+ the E⁰red is -.76 while the E⁰ox is .76; thus when you add these together to get the E⁰cell, they cancel out.

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As Q increases, Ecell increases or decreases?

As Q increases, Ecell decreases.

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A Voltaic Cell is also known as a:

(A) Concentration Cell

(B) Galvanic Cell

(D) Electrolytic Cell

(B) Galvanic Cell

A Voltaic Cell is also known as a Galvanic Cell.

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What is the purpose of a Galvanic Cell as compared to an Electrolytic Cell?

The purpose of a Galvanic/Voltaic Cell is to use a spontaneous reaction to produce an electric current (resulting in energy).

The purpose of an Electrolytic Cell is to use an Electric Current (aka energy) to drive a non-spontaneous reaction.

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True or False. Oxidation always occurs at the Anode and Reduction always occurs at the Cathode.

True. Whether you are dealing with a Galvanic Cell or an Electrolytic Cell, Oxidation always occurs at the Anode and Reduction always occurs at the Cathode.

<p>True. Whether you are dealing with a Galvanic Cell or an Electrolytic Cell, Oxidation always occurs at the Anode and Reduction always occurs at the Cathode.</p>

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The Standard Cell Potential for an Electrolytic Cell is equal to -5.4. Which of the following batteries could be used to drive the reaction forward?

I. 14.2 Volts

II. 8.3 Volts

III. 4.8 Volts

(A) I Only

(B) I and II Only

(D) I, II, and III

(B) I and II Only

You would need a battery with at least as much voltage as the Standard Cell Potential, which is -5.4 in this case.

Note that the Standard Cell Potential is negative, because this is a non-spontaneous reaction.

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You have Copper (E⁰red = .34) and Zinc (E⁰red = -.76) in a Galvanic Cell. In this case, Copper will be ________________. You also have Copper and Zinc in an Electrolytic Cell. In this case, Copper will be ________________.

Standard Reduction Potentials Chart:

(A) Reduced, Reduced

(B) Oxidized, Oxidized

(D) Oxidized, Reduced

You have Copper (E⁰red = .34) and Zinc (E⁰red = -.76) in a Galvanic Cell. In this case, Copper will be reduced. You also have Copper and Zinc in an Electrolytic Cell. In this case, Copper will be oxidized.

Copper is reduced in a Galvanic Cell because is has a higher E⁰red, which means it is more prone to be spontaneously reduced than Zinc. In an Electrolytic Cell, we are driving the non-spontaneous reaction, which would be opposite to the Galvanic Cell; thus, oxidizing the Copper.

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In a Galvanic Cell, the Anode is ____________ charged. And in an Electrolytic Cell, the Anode is ____________ charged.

(A) Positively, Positively

(B) Negatively, Negatively

(D) Negatively, Positively

For a Galvanic Cell, the electrons will flow away from the negatively charged Anode to the positively charged Cathode so that Reduction (gain of electrons) can occur there.

In an Electrolytic Cell, the electrons are sent from the battery to the negatively charged Cathode so that reduction can occur there. Thus, the Anode must positive. Remember that the negative terminal of the battery will be on the same side as the negative electrode and vice versa.

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What equation can be used to relate Standard Gibbs Free Energy to Gibb's Free Energy?

∆G = ∆G⁰ + RTlnQ

∆G = Gibbs Free Energy

∆G⁰ = Standard Gibb's Free Energy

R = Gas Constant (8.314 J/mol⋅K)

T = Temperature (298 K under standard conditions)

Q = Reaction Quotient

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What equation can be used to relate Standard Gibbs Free Energy to Standard Cell Potential?

∆G⁰ = -nFE⁰cell

∆G⁰ = Standard Gibbs Free Energy

n = Number of Electrons

F = Faraday's Constant (96,500 C / mol e-)

E⁰cell = Standard Cell Potential

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What equation can be used to relate Gibbs Free Energy to Cell Potential?

∆G = -nFEcell

∆G = Gibbs Free Energy

n = Number of Electrons

F = Faraday's Constant (96,500 C / mol e-)

Ecell = Cell Potential

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What is the Cell Potential for a reaction in which Zn2+ is reduced and the ∆G⁰ is equal to -253.7 J/mol and the Reaction Quotient is equal to 0.32?

(A) -.030

(B) -.015

(D) .030

∆G = ∆G⁰ + RTlnQ

Because of the units used here, we will use R = 8.314 J/(K⋅mol)

∆G = -253.7 + (8.314⋅298⋅ln.32)

∆G = -253.7 + (8.314⋅298⋅-1 (actual: -1.139))

∆G = -253.7 + (-3000) (actual: -2821.95)

∆G = approx. -3250 (actual: -3075.65)

∆G = -nFEcell

-3,250 = -2⋅96,500⋅Ecell

Ecell = -3250 / -200,000

Ecell = approx. .015 (actual: .01538)

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As Q increases, G increases or decreases?

As Q increases, G increases.

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When G = 0, what is Ecell?

When G = 0, Ecell will also = 0.

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A current of 3.2 A is applied to an Electrolytic Cell containing Copper (E⁰red = .34) and Zinc (E⁰red = -.76). How many grams of Zinc will be deposited after 7.2 hours? (periodic table: http://www.sbcs.qmul.ac.uk/iupac/AtWt/table.gif)

(A) 28.1

(B) 17.2

(D) 2.1

(A) 28.1

7.2 hours ⋅ 60 minutes / 1 hour ⋅ 60 seconds / 1 minute ⋅ 3.2 C / s ⋅ 1 mol e- / 96,500 C ⋅ 1 mol Zn2+ / 2 mol e- ⋅ 65.39 g Zn(s) / 1 mol Zn2+ = 30 g Zn(s) (actual: 28.1)

Note: Although there is an equation you can memorize for this, I prefer simply using Dimensional Analysis.

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How many hours would it take to form 5.34 moles of Zn(s) when a current of 9.8 A is applied to an Electrolytic Cell containing Copper (E⁰red = .34) and Zinc (E⁰red = -.76)? (periodic table: http://www.sbcs.qmul.ac.uk/iupac/AtWt/table.gif)

(A) 17.6

(B) 29.2

(D) 213.8

(B) 29.2

5.34 moles Zn(s) ⋅ 2 moles e- / 1 mole Zn2+ ⋅ 96,500 C / 1 mole e- ⋅ 1 second / 9.8 C ⋅ 1 minute / 60 seconds ⋅ 1 hour / 60 minutes = 30 hours (actual: 29.2)

Note: Although there is an equation you can memorize for this, I prefer simply using Dimensional Analysis.

Need help with MCAT math? Become an MCAT math wizard using Andrew's High-speed Math Mastery Course @ https://mcatselfprep.com/course/andrews-high-speed-math-mastery-course/

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Label a soundwave with the following terms:

(1) Amplitude

(2) Wavelength

(3) Equilibrium Position

Soundwave visual: http://www.mediacollege.com/audio/images/loudspeaker-waveform.gif

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Compare Frequency and Period.

Frequency is the number of wavelengths per second.

Period is the number of seconds it takes for one wavelength to pass.

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What equation can be used to calculate the Frequency (f) from the Period (T)?

f = 1/T

f = Frequency (s^-1 or Hz)

T = Period (sec)

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The Frequency is 5.43⋅10^14. What is the Period?

(A) -1.84⋅10^-15

(B) -5.43⋅10^-14

(D) 5.43⋅10^-14

f = 1/T

5.43⋅10^14 = 1/T

T = 1 / 5.43⋅10^14

T = .2 ⋅ 10^-14

T = approx. 2 ⋅ 10^-15 seconds (actual: 1.84 ⋅ 10^-15)

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As frequency increases, the pitch becomes:

(A) Louder

(B) Softer

(D) Lower

Frequency is related to Pitch whereas Intensity is related to Loudness.

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CRB Which of the following will affect how an individual perceives the Loudness/Intensity of soundwaves?

I. Brain Function

II. Stiffening of the Ossicles

III. Damage to Cochlear Hair Cells

(A) III only

(B) I and II only

(D) I, II and III

Each of the following can impact how an individual perceives the Loudness/Intensity of sound waves:

I. Brain Function

II. Stiffening of the Ossicles

III. Damage to Cochlear Hair Cells

IV. Obstructing the Ear Canal

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What is the lowest frequency of sound that it is possible to hear? Highest?

Lowest: 20 Hz

Highest: 20,000 Hz

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CRB Fill in the blanks: ____________ Waves would fall below the hearing ranges of humans (20Hz - 20kHz), whereas ___________ Waves have frequencies above 20kHz.

(A) Intersonic, Ultrasonic

(B) Intersonic, Extrasonic

(D) Infrasonic, Extrasonic

Infrasonic Waves would fall below the hearing ranges of humans (20Hz - 20kHz), whereas Ultrasonic Waves have frequencies above 20kHz.

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CRB The Doppler Effect will be discussed in later sections, but for now, know that changing the distance between the source of the stimulus and the detector can influence the perceived frequency.

Fill in the blanks: One specialized scenario of the Doppler Effect is with _____________, when the sound waves are compressed and build up at the front of an object. This hitting and moving past the object will quickly change from very high to low pressures at the object, creating the sensation of a ______________.

(A) Earthquakes, Aftershock

(B) Shock Waves, Mach 1

(D) Shock Waves, Sonic Boom

One specialized scenario of the Doppler Effect is with Shock Waves, when the sound waves are compressed and build up at the front of an object. This hitting and moving past the object will quickly change from very high to low pressures at the object, creating the sensation of a Sonic Boom.

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Your professor teaches you that sound waves travel at a speed of 343 meters/second. What is he really saying?

(A) The air particles affected by the sound wave are moving at 343 meters per second

(B) Your Tympanic Membrane is oscillating 343 times per second as you hear that sound.

(D) The light affected by the sound wave is moving at a speed of 343 meters per second.

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CRB In which of the following medium conditions would the speed of sound be the Slowest?

(A) High-Density Solid

(B) High-Density Gas

(D) Low-Density Gas

(B) High-Density Gas

Because there is more inertia with all of the dense gas particles, a High-Density Gas would be the slowest medium for sound to travel through.

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CRB Fill in the blanks: A ____________ Wave is known for having particles oscillate perpendicular to the direction of propagation (ex: moving up and down if propagating left to right), whereas a ___________ Wave is known for oscillating parallel to the direction of propagation.

(A) Up-down, Long

(B) Orthogonal, Direct

(D) Transverse, Longitudinal

A Transverse Wave is known for having particles oscillate perpendicular to the direction of propagation (ex: moving up and down if propagating left to right), whereas a Longitudinal Wave is known for oscillating parallel to the direction of propagation.

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Sound is considered a ___________ wave, and a vibrating guitar string is considered a ___________ wave.

(A) Transverse, Transverse

(B) Longitudinal, Longitudinal

(D) Longitudinal, Transverse

Sound is considered a Longitudinal wave, and a vibrating guitar string is considered a Transverse wave.

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CRB Jemele is arguing with a physicist that, even at Absolute Zero, sound would still be able to travel. How should the Physicist disprove Jemele?

Sound is transmitted by oscillating particles in a deformable medium. If the medium is at Absolute Zero, then there is no movement at all, including no oscillation possible.

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What equation can be used to relate the Speed of a Wave (v) to the Wavelength (λ)?

v = λf

v = Speed of Wave

λ = Wavelength

f = Frequency

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How does the equation v = x/t relate to the equation v = λf?

v = x/t = λ/T = λf

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You double the frequency of a sound wave, the velocity of the sound wave will:

(A) quadruple.

(B) double.

(D) halve.

The velocity will not change, but the wavelength will divide in half.

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You double the amplitude of a sound wave, the velocity of the sound wave will:

(A) quadruple.

(B) double.

(D) halve.

The only way to change the velocity of a sound wave is to change the medium (i.e. air, water, etc) that the wave is travelling through.

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What two properties of the medium can change the speed of the sound wave?

(1) Stiffness (Resistance to Compression)

(2) Density

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What equation is used to relate these two factors to the speed of a wave?

v = √B/ρ

v = Velocity of Wave

B = The Bulk Modulus (Resistance of a Wave to Compression)

ρ = Density

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How will increasing the stiffness of a medium affect the speed of sound?

Increasing the stiffness will increase the speed of sound because the particles are more interconnected, making for a faster transmission through the medium.

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How will increasing the density of a medium affect the speed of sound?

Increasing the density of a medium will decrease the speed of sound through that medium due to the fact that each particle will weigh more and thus move more slowly.

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Jimmy puts his ear down on the iron metal of a large railroad. His buddy Bill strikes the railroad with a stick about 100 meters away from him. Which of the following is true?

(A) Jimmy will hear the sound through the air faster than the sound through the metal.

(B) Jimmy will hear the sound through the metal faster than the sound through the air.

(D) Jimmy will hear the sound through the metal at almost the same time as he hears the sound through the air.

(B) Jimmy will hear the sound through the metal faster than the sound through the air.

Although Iron has a higher density than air, its Bulk Modulus is much much larger than air, resulting in a much higher speed of sound through iron.

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Put the following in order of slowest to fastest:

I. Velocity of Sound in a Solid

II. Velocity of Sound in a Liquid

III. Velocity of Sound in a Gas

(A) I < II < III

(B) II < I < III

(D) III < I < II

In order of slowest to fastest:

Velocity of Sound in a Gas < Velocity of Sound in a Liquid < Velocity of Sound in a Solid

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You increase the Temperature of the air, what will happen to the Speed of Sound?

The Speed of Sound will increase, because the density of the air will decrease as you heat up the air.

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What is the purpose of the Decibel Scale?

Much like the pH scale is used to convert the concentration of H+ into more manageable numbers, the purpose of the Decibel Scale is to convert the Intensity of Sound into more manageable numbers.

<p>Much like the pH scale is used to convert the concentration of H+ into more manageable numbers, the purpose of the Decibel Scale is to convert the Intensity of Sound into more manageable numbers.</p>

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What equation can be used to convert intensity into Decibels?

β = 10log(I/I₀)

β = Decibels (dB)

I = Intensity

I₀ = Threshold of Human Hearing (1⋅10^-12 W/m^2)

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A seagull screeches with an intensity of 4.32⋅10^-3 W/m^2. With how many Decibels did the seagull screech?

(A) 43.8

(B) 64.2

(D) 113.8

β = 10log(I/I₀)

β = 10log(4.32⋅10^-3/1⋅10^-12)

β = 10log(4.32⋅10^9)

β = 10(log(4.32⋅10^9))

β = 10(9.6 (actual: 9.64))

β = 96 (actual: 96.4))

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You can scream at 46 Decibels. Your roommate can scream at 56 Decibels. Your roommate can scream ___x louder than you.

(A) 1

(B) 10

(D) 1,000

(B) 10

Think about the Logarithmic Scale.

10 Decibels louder is equal to 10x louder.

20 Decibels louder is equal to 100x louder.

30 Decibels louder is equal to 1,000x louder.

And so on...

<p>(B) 10</p><p>Think about the Logarithmic Scale.</p><p>10 Decibels louder is equal to 10x louder.</p><p>20 Decibels louder is equal to 100x louder.</p><p>30 Decibels louder is equal to 1,000x louder.</p><p>And so on...</p>

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Why is it called DECIbels?

It is called DECIbels because it is the log multiplied by 10. "Deci-" means 10.

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What equation is used to relate Radius/Distance from the sound to Intensity?

I = P / (4πr^2)

I = Intensity

P = Power

r = Radius

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CRB How would doubling the amplitude affect the intensity of a sound wave?

(A) Cut it in half

(B) Double the intensity

(D) No effect

Intensity is proportional to Amplitude Squared, so doubling the Amplitude will Quadruple the Intensity.

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CRB If you quadrupled (4x) the Amplitude of a Sound Wave, how many decibels would the sound's loudness increase by?

(A) 1.2 dB

(B) 1.6 dB

(D) 16 dB

Intensity is related to Amplitude squared

4^2 = 16

log (16) = 1.2 [approx 1]

Recall that this is the DECIbel system, though, so it is a logarithmic scale times 10. So, the Loudness actually increases by 12 dB!

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You are standing directly in front of a speaker at a rock concert. The intensity of the speaker is 100 Decibels. You decide that your ears have bled quite enough, so you take a step back doubling the distance between you and the speaker. What is the new intensity of the sound in Decibels (dB)?

(A) 94

(B) 90

(D) 25

(A) 94

β = 10log(I/I₀)

100 = 10log(I/1⋅10^-12)

I = 1⋅10^-2

The Intensity is proportional to the Radius according the relationship I ∝ 1/r^2. This indicates that if the radius doubles, the intensity must decrease by a factor of 4, making the intensity equal to 2.5⋅10^-3.

β = 10log(I/I₀)

β = 10log(2.5⋅10^-3/1⋅10^-12)

β = 10log(2.5⋅10^9)

β = 10(9.25 (actual: 9.40))

β = 92.5 (actual: 94.0)

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You are at a rock concert, and you are standing just 2.3 meters away from the speaker. If the sound wave reaching your ear has an intensity of 4.5⋅10^-5 W/m^2, what is the power of the speaker?

(A) 2.99⋅10^-3 W

(B) 6.43⋅10^-3 W

(D) 5.44⋅10^-4 W

(A) 2.99⋅10^-3 W

I = P / (4πr^2)

4.5⋅10^-5 = P / (4⋅3.14⋅2.3^2)

4.5⋅10^-5 = P / (60 (actual: 66.44)

P = 270⋅10^-5 (actual: 298.98⋅10^-5 W)

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What results in some of the energy of the sound wave being converted into thermal energy? How does this affect our relationship of I ∝ 1/r^2?

Due to friction, some of the sound energy is converted into thermal energy. This results in even less intensity as predicted by our relationship of I ∝ 1/r^2.

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This idea of intensity being lost to friction is known as:

(A) Enthalpy

(B) Attenuation

(D) Fluxation

(B) Attenuation

This idea of intensity being lost to friction is known as Attenuation.

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Ultrasound refers to what?

(A) Sound with a frequency above that of 2,000 Hz.

(B) Sound with a frequency above that of 20,000 Hz.

(D) Sound with an intensity above that of 20,000 W.

(B) Sound with a frequency above that of 20,000 Hz.

Ultrasound refers to sound with a frequency above that of 20,000 Hz.

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How does Ultrasound work?

It uses Ultrasound frequency sound waves to determine the structure of body tissues. It is based on the idea that sound waves will reflect upon hitting the interface between two mediums. The detector uses the speed of sound and the amount of time it took the wave to reflect back to calculate the location of that object.