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Intensity of sound (not included in caps - advanced)

Advanced section

This section is more advanced than required and is best revisited for interest only when you are comfortable with concepts like power and logarithms.

Intensity is one indicator of amplitude. Intensity is the energy transmitted over a unit of area each second.

Intensity

Intensity is defined as:

Intensity = energy time × area = power area

By the definition of intensity, we can see that the units of intensity are

Joules s · m 2 = Watts m 2

The unit of intensity is the decibel (symbol: dB). This reduces to an SI equivalent of W · m - 2 .

The average threshold of hearing is 10 - 12 W · m - 2 . Below this intensity, the sound is too soft for the ear to hear. The threshold of pain is 1 . 0 W · m - 2 . Above this intensity a sound is so loud it becomes uncomfortable for the ear.

Notice that there is a factor of 10 12 between the thresholds of hearing and pain. This is one reason we define the decibel (dB) scale.

Db scale

The intensity in dB of a sound of intensity I , is given by:

β = 10 log I I o I o = 10 - 12 W · m - 2

In this way we can compress the whole hearing intensity scale into a range from 0 dB to 120 dB.

Examples of sound intensities.
Source Intensity (dB) Times greater than hearing threshold
Rocket Launch 180 10 18
Jet Plane 140 10 14
Threshold of Pain 120 10 12
Rock Band 110 10 11
Subway Train 90 10 9
Factory 80 10 8
City Traffic 70 10 7
Normal Conversation 60 10 6
Library 40 10 4
Whisper 20 10 2
Threshold of hearing 0 0

Notice that there are sounds which exceed the threshold of pain. Exposure to these sounds can cause immediate damage to hearing.In fact, exposure to sounds from 80 dB and above can damage hearing over time. Measurescan be taken to avoid damage, such as wearing earplugs or ear muffs. Limiting exposure time andincreasing distance between you and the source are also important steps for protecting your hearing.

Discussion : importance of safety equipment

Working in groups of 5, discuss the importance of safety equipment such as ear protectors for workers in loud environments, e.g. those who use jack hammers or direct aeroplanes to their parking bays. Write up your conclusions in a one page report. Some prior research into the importance of safety equipment might be necessary to complete this group discussion.

Summary

  1. Sound waves are longitudinal waves
  2. The frequency of a sound is an indication of how high or low the pitch of the sound is.
  3. The human ear can hear frequencies from 20 to 20 000 Hz. Infrasound waves have frequencies lower than 20 Hz. Ultrasound waves have frequencies higher than 20 000 Hz.
  4. The amplitude of a sound determines its loudness or volume.
  5. The tone is a measure of the quality of a sound wave.
  6. The speed of sound in air is around 340 m · s - 1 . It is dependent on the temperature, height above sea level and the phase of the medium through which it is travelling.
  7. Sound travels faster when the medium is hot.
  8. Sound travels faster in a solid than a liquid and faster in a liquid than in a gas.
  9. Sound travels faster at sea level where the air pressure is higher.
  10. The intensity of a sound is the energy transmitted over a certain area. Intensity is a measure of frequency.
  11. Ultrasound can be used to form pictures of things we cannot see, like unborn babies or tumors.
  12. Echolocation is used by animals such as dolphins and bats to “see” their surroundings by using ultrasound.
  13. Ships use sonar to determine how deep the ocean is or to locate shoals of fish.

Exercises

  1. Choose a word from column B that best describes the concept in column A.
    Column A Column B
    pitch of sound amplitude
    loudness of sound frequency
    quality of sound speed
    waveform
  2. A tuning fork, a violin string and a loudspeaker are producing sounds. This is because they are all in a state of:
    1. compression
    2. rarefaction
    3. rotation
    4. tension
    5. vibration
  3. What would a drummer do to make the sound of a drum give a note of lower pitch?
    1. hit the drum harder
    2. hit the drum less hard
    3. hit the drum near the edge
    4. loosen the drum skin
    5. tighten the drum skin
  4. What is the approximate range of audible frequencies for a healthy human?
    1. 0.2 Hz 200 Hz
    2. 2 Hz 2 000 Hz
    3. 20 Hz 20 000 Hz
    4. 200 Hz 200 000 Hz
    5. 2 000 Hz 2 000 000 Hz
  5. X and Y are different wave motions. In air, X travels much faster than Y but has a much shorter wavelength. Which types of wave motion could X and Y be?
    X Y
    A microwaves red light
    B radio infra red
    C red light sound
    D sound ultraviolet
    E ultraviolet radio
  6. Astronauts are in a spaceship orbiting the moon. They see an explosion on the surface of the moon. Why can they not hear the explosion?
    1. explosions do not occur in space
    2. sound cannot travel through a vacuum
    3. sound is reflected away from the spaceship
    4. sound travels too quickly in space to affect the ear drum
    5. the spaceship would be moving at a supersonic speed
  7. A man stands between two cliffs as shown in the diagram and claps his hands once.
    Assuming that the velocity of sound is 330 m · s - 1 , what will be the time interval between the two loudest echoes?
    1. 2 3 s
    2. 1 6 s
    3. 5 6 s
    4. 1 s
    5. 1 3 s
  8. A dolphin emits an ultrasonic wave with frequency of 0,15 MHz. The speed of the ultrasonic wave in water is 1 500 m · s - 1 . What is the wavelength of this wave in water?
    1. 0,1 mm
    2. 1 cm
    3. 10 cm
    4. 10 m
    5. 100 m
  9. The amplitude and frequency of a sound wave are both increased. How are the loudness and pitch of the sound affected?
    loudness pitch
    A increased raised
    B increased unchanged
    C increased lowered
    D decreased raised
    E decreased lowered
  10. A jet fighter travels slower than the speed of sound. Its speed is said to be:
    1. Mach 1
    2. supersonic
    3. subsonic
    4. hypersonic
    5. infrasonic
  11. A sound wave is different from a light wave in that a sound wave is:
    1. produced by a vibrating object and a light wave is not.
    2. not capable of traveling through a vacuum.
    3. not capable of diffracting and a light wave is.
    4. capable of existing with a variety of frequencies and a light wave has a single frequency.
  12. At the same temperature, sound waves have the fastest speed in:
    1. rock
    2. milk
    3. oxygen
    4. sand
  13. Two sound waves are traveling through a container of nitrogen gas. The first wave has a wavelength of 1,5 m, while the second wave has a wavelength of 4,5 m. The velocity of the second wave must be:
    1. 1 9 the velocity of the first wave.
    2. 1 3 the velocity of the first wave.
    3. the same as the velocity of the first wave.
    4. three times larger than the velocity of the first wave.
    5. nine times larger than the velocity of the first wave.
  14. Sound travels at a speed of 340 m · s - 1 . A straw is 0,25 m long. The standing wave set up in such a straw with one end closed has a wavelength of 1,0 m. The standing wave set up in such a straw with both ends open has a wavelength of 0,50 m.
    1. calculate the frequency of the sound created when you blow across the straw with the bottom end closed.
    2. calculate the frequency of the sound created when you blow across the straw with the bottom end open.
  15. A lightning storm creates both lightning and thunder. You see the lightning almost immediately since light travels at 3 × 10 8 m · s - 1 . After seeing the lightning, you count 5 s and then you hear the thunder. Calculate the distance to the location of the storm.
  16. A person is yelling from a second story window to another person standing at the garden gate, 50 m away. If the speed of sound is 344 m · s - 1 , how long does it take the sound to reach the person standing at the gate?
  17. A piece of equipment has a warning label on it that says, "Caution! This instrument produces 140 decibels." What safety precaution should you take before you turn on the instrument?
  18. What property of sound is a measure of the amount of energy carried by a sound wave?
  19. Person 1 speaks to person 2. Explain how the sound is created by person 1 and how it is possible for person 2 to hear the conversation.
  20. Sound cannot travel in space. Discuss what other modes of communication astronauts can use when they are outside the space shuttle?
  21. An automatic focus camera uses an ultrasonic sound wave to focus on objects. The camera sends out sound waves which are reflected off distant objects and return to the camera. A sensor detects the time it takes for the waves to return and then determines the distance an object is from the camera. If a sound wave (speed = 344 m · s - 1 ) returns to the camera 0,150 s after leaving the camera, how far away is the object?
  22. Calculate the frequency (in Hz) and wavelength of the annoying sound made by a mosquito when it beats its wings at the average rate of 600 wing beats per second. Assume the speed of the sound waves is 344 m · s - 1 .
  23. How does halving the frequency of a wave source affect the speed of the waves?
  24. Humans can detect frequencies as high as 20 000 Hz. Assuming the speed of sound in air is 344 m · s - 1 , calculate the wavelength of the sound corresponding to the upper range of audible hearing.
  25. An elephant trumpets at 10 Hz. Assuming the speed of sound in air is 344 m · s - 1 , calculate the wavelength of this infrasonic sound wave made by the elephant.
  26. A ship sends a signal out to determine the depth of the ocean. The signal returns 2,5 seconds later. If sound travels at 1450 m.s - 1 in sea water, how deep is the ocean at that point?

Questions & Answers

What is randomization
Joseph Reply
definition of stimulus
Thomas Reply
please explain me clinical studies
abril Reply
clinical studies are people who evaluate behavior, medical, and surgical intervention
Connie
clinical studies are people who evaluate behavior, medical, and surgical intervention
Connie
what are the characteristics of learning?
steve Reply
The ability to learn is one of the most outstanding human characteristics. Learning occurs continuously throughout a person’s lifetime. To understand how people learn, it is necessary to understand what happens to the individual during the process. In spite of numerous theories and contrasting views
MUBARAK
Psychologists generally agree there are many characteristics of learning.
MUBARAK
Learning is the process by which one acquires, ingests, and stores or accepts information. The main characteristic of learning that; it is a process of obtaining knowledge to change human behavior through interaction, practice, and experience.
MUBARAK
Our experiences with learned information compose our bodies of knowledge.
MUBARAK
Is there not one universal understanding or relatable emotion whether physical or communicated verbally they could Trigger empathy?
Tory
what is immune system
Amanda Reply
a complex network of cells that protects the body against infection
Stephen
Sorry. Cells and proteins
Stephen
what is perspectives
acholonu Reply
someones point of view the way ur brain sees the way situations unfold
Echo
perspective is your view on topics
Trish
Perspective is your opinion on certain situations
Connie
your perspective is your interpretation of what is being said and done around you and how you hear and view them .
Jim
is this in reference to any particular use of the word? Because there are also the 7 major "perspectives" in psychology: psychodynamic, cognitive, behavioral, biological, cross-cultural, evolutionary, & humanistic
Alex
aren't they like schemas of the world, the future and yourself
naina
Perspective is your opinion on things that you feel, think or hear.
hiba
I'm trying to write a paper about video game and violence and suggestions or researches would help with this
rebal
do you also have to write about aggression and how its linked to video games and violence
naina
because for alevel psychology we could have a 16 marker essay for how media influences aggression which basically includes video games and violence on tv shows
naina
yes basically I'm arguing that video games cause violence not necessarily in a direct way but it plays apart. I'm trying to oppose the popular opinion of video games doesn't cause violence
rebal
It's not connected that much actually tbh
Kira
the way we think
according to my textbook rebal
naina
there is a lab study by Craig an Anderson- computer games mortal combat
naina
Matt delisi et al did a correlation study
naina
Lindsay Robertson et al - longitudinal study
naina
Craig Anderson also did a meta analysis of 136 studies
naina
I will check them thanks naina
rebal
Yes, that would be my recommendation.
Ashley Reply
merits and demerits of observation as a method of studying human behavior in education psychology
Khadija Reply
what is psychology
Khadija
psychology: scientific study of behaviour and mental processes.
Ahmed
how to mind reading?
UMESH
how to face reading
UMESH
energy and thought will give mind spirit and proper exercises , flexibility and making mind readind easier
Ahmed
How to read microexpresions easier?
Edg
scope of educationnalpsycology
USMAN
seriously i will pay someone to do an essay for me my god i need help so much 😪😪😪
dearbhlagh
what do you need help with ?
Keiko
The better question is how much?
Pixeled
🥒🍑😩💦
Jacob
hey all I'm Beth I just started psych 101 have 1st test any suggestions I should memorize ?
Bethany Reply
memorize dememorizing
devesh
how the blinds person his dream
Ahmed
Hi! I started as well
La
what is prototype
Arnav Reply
what is event schema
Arnav
Event schema is how you deal with situations is this installation is good you gonna handle a great but if it's badd you have to be strong I handle it the best way you can and stay positive
Connie
why do we adapt to negative events more quickly as compared to the positive ones?
Fareha
The negative ones are easier to adapt because of the people the we surround ourselves with if we surround ourselves with negative people who go to see things negatively but if we surround ourselves with positive people we are going to see things more positive
Connie
oh ok thanks!
Fareha
your welcome
Connie
what are the remedy for ADHD
anagha Reply
methylphenidate
Maryjade
counter conditioning
gad Reply
it is d conditioning were u add an unpleasant stimulus ad a pleasant stimulus to give a good response. eg a girl that hate or fears snake u add her mom to d picture because she loves her mother she gradually tends to like snake
dalusi
can I get an update on the discussion at hand
Segun
I'd like one as well, please
Trish
I third this.
Redacted
you guys could refer to a research by Mary Cover Jones. she did a study on counter conditioning.
Shubhra
i too would like to get an update on the dicussion please
Connie
so basically we are discussing about counter conditioning. if you all know about classical conditioning which was done by pavlov, later a similar thing was done by JB Watson, but on a child. this child was made to learn a phobia.
Shubhra
after his unethical experiment, his student mary cover jones also did an experiment where she proved, if a fear can be learnt, it can also be unlearn. hence, counter conditioning. where a negative stimulus (any fearful object) is followed by a pleasant stimulus (eg food).
Shubhra
After several pairings, the fear is neutralized.
Shubhra
hey, i wanted to know in positive counter conditioning a several trials are done to make the person unlearn their phobias but in aversive (-ve) counter conditioning,after just 1 trial a person learns that behaviour, why the negative behaviour is learnt in just 1 try?
Fareha
Please what is randomization?
Joseph
hi, may I have many MCQ?
Ango Reply
hi
Teri
what would you like to know
Connie
We want to know everything
victor
what's MCQ?
Ronah
Multiple Chouce Questiom
Connie
Who knows something about Multiple Personality Disorder ?
victor
Victor what you want to know in it
Brindhu
Everything you know about it.
victor
what you know about functionalism
Teri
@ Victor. Dissociative identity disorder or multiple personality disorder has two or more distinct personality states.they may be disconnected among thoughts, identity, consciousness and memory .this could be happened when to trauma of childhood incident or any other impact in life
Brindhu
how do you identify these altars ? and how do you easily identify MPD patient ?
victor
what is experimental bias
Teri
experimental bias is when you experiment with something and you like it and tell someone else about it and you tell them ira good even though they don't have the same reacton to it that you did
Connie
define Experiment
Teri
Experiment is trying something new you don't know how it's gonna work out or even if it will work or if it won't so you try it anyway it's sometimes it works and sometimes it doesn't
Connie
what is the difference between CBT and REBT
Zeeshan Reply
what it means to survive danger
Bonsa Reply
it's called bystander effect when people reject you
Jason
hey Jason
Bonsa
There are 2 meanings of surviving danger one is to be stronger than you were when you went in and the 2nd is a to have your wits about you and to keep yourself from getting into danger in the 1st place but if you have to be in danger Use your best common knowledge to get out of it
Connie
how do I overcome my fears of public speaking
Bonsa
There's many theories to that as well many people say the picture the audience in their underwear but that does not always work so what I do is I forget about the people in the audience and pretend like I'm by myself and you gonna find yourself about more comfortable and a lot more at ease
Connie
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Source:  OpenStax, Physics - grade 10 [caps 2011]. OpenStax CNX. Jun 14, 2011 Download for free at http://cnx.org/content/col11298/1.3
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