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DEVIL PHYSICS
THE BADDEST CLASS ON CAMPUS
IB PHYSICS
TSOKOS OPTION I-1
THE EAR AND HEARING
IB Assessment Statements
Option I-1, The Ear and Hearing:
I.1.1. Describe the basic structure of the human
ear.
I.1.2. State and explain how sound pressure
variations in the air are changed into larger
pressure variations in the cochlear fluid.
I.1.3. State the range of audible frequencies
experienced by a person with normal
hearing.
I.1.4. State and explain that a change in observed
loudness is the response of the ear to a
change in intensity.
IB Assessment Statements
Option I-1, The Ear and Hearing:
I.1.5. State and explain that there is a
logarithmic response of the ear to
intensity.
I.1.6. Define intensity and intensity level (IL).
I.1.7. State the approximate magnitude of the
intensity level at which discomfort is
experienced by a person with normal
hearing.
IB Assessment Statements
Option I-1, The Ear and Hearing:
I.1.8. Solve problems involving intensity levels.
I.1.9. Describe the effects on hearing of shortterm and long-term exposure to noise.
I.1.10. Analyze and give a simple interpretation
of graphs where IL is plotted against the
logarithm of frequency for normal and for
defective hearing.
Objectives:
 Lesson Objectives. By the end of this
class you should be able to:
 Describe the basic components of the
human ear
 Define sound intensity and the sound
intensity scale based on the decibel
 Perform calculations with intensity and the
decibel scale
Objectives:
 Understand how the ear functions
 Describe how the ear separates sound
according to frequency in the cochlea
 State the meaning of the terms threshold of
hearing and audiogram
Introductory Video
Macroscopic View of the Ear
 Ear is sensitive to sounds ranging from 20 Hz to
20,000 Hz
 At 1000 Hz, the ear can pick up sound vibrations
that displace the eardrum by 1/10th the diameter
of a hydrogen atom
 Outer ear
 Middle ear
 Inner ear
 Eustachian tube serves to equalize pressure
 Airplanes
 Scuba Diving
 Semicircular canals do not contribute to hearing
 Provide us with a sense of balance
The Ear and Balance
Schematic Diagram of the Ear
Figure I1.2, Schematic
Diagram of the Ear
 Ossicles are three small bones: malleus, incus
and stapes – smallest in human body
 Purpose is to amplify amplitude of sound waves
by a factor of 1.5
Figure I1.2, Schematic
Diagram of the Ear
 Area difference between eardrum and oval
window increases amplification by 13
 Total amplification = 20x
 Acoustic reflex – muscles limit ossicle movement
 Does not protect from instantaneous sound
Figure I1.2, Schematic
Diagram of the Ear
 Cochlea is where hearing takes place
 Vestibular, Helicotrema and Tympanic canals
(2cm long)
 Round window is pressure release point
Figure I1.2, Schematic
Diagram of the Ear
 Scala media or cochlean duct runs between
canals
 Covered by the basilar membrane
 Contains nerve endings which convert sound waves
into electrical signals sent to the brain
Figure I1.2, Schematic
Diagram of the Ear
 Basilar membrane
 Organ of Corti responsible for converting vibrations
into electrical signals
 Different parts are sensitive to different frequency
ranges
Mismatch of Impedances
 Sound travels differently in different media
 In hearing, sound goes from air to the fluid in
the inner ear
 The term impedance is used to describe the
difference in sound in different media
 Acoustic Impedance:
 ρ is density
 c is speed of sound
Z  c
Mismatch of Impedances
 When sound transitions to a new media,
differences in impedances will cause some of
the sound to be reflected
 More sound is transmitted when impedances
are matched
 Impedance before oval window is 450 kg/m2s
 Impedance after oval window is 1.5 x 106
kg/m2s
Mismatch of Impedances
 Because of the difference in the impedances,
the sound must be amplified by the ossicles
and by the differences in area between the
eardrum and the oval window
Complex Sounds
Complex Sounds
 Any periodic function can be written as a sum
of harmonic functions
 Complex sounds can be decomposed into
component frequencies of the harmonic
function
 This is what is done in the cochlea
 The sound is then reconstructed in the brain
Intensity of Sound
Sensation of Hearing
 Hearing does not increase linearly with
intensity
 It is a logarithmic function
 Increase in hearing is proportional to the
fractional increase in intensity (WeberFechner law)
 This give us the decibel scale
Sensation of Hearing
 An increase of 10 dB equates to an increase in
intensity by a factor of 10
 I0 refers to the threshold of hearing, 1 x 10-12
W/m2
Frequency Response and Loudness
 The normal hearing range is 20 Hz to 20,000
Hz
 The threshold of hearing reduces with age
Frequency Response and Loudness
 The threshold of hearing of 1 x 10-12 W/m2 is
based on 1000 Hz
 Sounds of greater or lesser intensity may be
heard depending on frequency
Threshold of Hearing Curve
Threshold of Hearing
Threshold of Hearing
 Hearing sensitivity can best be understood
based on resonance in the ear canal
 Think of it as a closed-end tube where the
fundamental wavelength is 4L
Threshold of Hearing
 The length of the ear canal is 2.8 cm
  4 L  4 x 0 . 028  0 . 112
f 
c


340
0 . 112
 3036 Hz
Pitch
 Subjective
 How high or low a sound is
 Primarily determined by frequency, but also
by intensity
Frequency Separation in Cochlea
 The basilar membrane decreases in stiffness
along its length (35mm)
 Velocity of sound is high at the beginning of
the canal and drops along the length
 Response by the organ of Corti is greatest to
sounds that are resonant
Frequency Separation in Cochlea
Frequency Separation in Cochlea
Hearing Defects
 Sensory Nerve Deafness
 Damage to hair cells and neural pathways
 Tumors of the acoustic nerve or meningitis
 Conduction Deafness
 Damage to the middle ear
 Blockage (full or partial) of the auditory canal
 Bone disease to the ossicles
 Hearing tested with an audiogram
Hearing Loss
 Aging
 Gently curved with smaller loss in decibels
 Damage
 More substantial loss, especially in higher
frequencies
Required Amplification
  45 dB
  10 log
I
I0
I  I 0 x10
4 .5
I  I 0 x 3 . 16 x10
4
Audiogram
 Steep curve
 Large high
frequency loss
indicates damage
due to overexposure
 Aging would show
shallow curve, less
overall loss
Audiogram
 Circles for air
 Triangles for bone
 Gap between the
two indicates a
conduction
problem in middle
or outer ear
Audiogram
 When the bone and
air graphs nearly
coincide, the
problem is most
likely a cochlear or
nerve problem in
the inner ear
Hearing Aids
 Used for conductive hearing loss where inner
ear is still functioning
 Amplifies sound within a limited range
 Mainly the range of human speech
 Doesn’t work well for much else
Cochlear Implant
 For sensory loss in the inner ear
 Consists of:
 Microphone
 Signal processor to convert sound to electrical
signals
 Electrodes surgically implanted in the cochlea
 Mimics the function of the cochlea
HAD ENOUGH?
OKAY, I HEAR YA!
Objectives:
 Lesson Objectives. By the end of this
class you should be able to:
 Describe the basic components of the
human ear
 Define sound intensity and the sound
intensity scale based on the decibel
 Perform calculations with intensity and the
decibel scale
Objectives:
 Understand how the ear functions
 Describe how the ear separates sound
according to frequency in the cochlea
 State the meaning of the terms threshold of
hearing and audiogram
IB Assessment Statements
Option I-1, The Ear and Hearing:
I.1.1. Describe the basic structure of the human
ear.
I.1.2. State and explain how sound pressure
variations in the air are changed into larger
pressure variations in the cochlear fluid.
I.1.3. State the range of audible frequencies
experienced by a person with normal
hearing.
I.1.4. State and explain that a change in observed
loudness is the response of the ear to a
change in intensity.
IB Assessment Statements
Option I-1, The Ear and Hearing:
I.1.5. State and explain that there is a
logarithmic response of the ear to
intensity.
I.1.6. Define intensity and intensity level (IL).
I.1.7. State the approximate magnitude of the
intensity level at which discomfort is
experienced by a person with normal
hearing.
IB Assessment Statements
Option I-1, The Ear and Hearing:
I.1.8. Solve problems involving intensity levels.
I.1.9. Describe the effects on hearing of shortterm and long-term exposure to noise.
I.1.10. Analyze and give a simple interpretation
of graphs where IL is plotted against the
logarithm of frequency for normal and for
defective hearing.
QUESTIONS
Homework
#1-9
STOPPED HERE ON 4/4/2013

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