ib assessment statements option i-1, the ear and hearing: i.1.1.describe the basic structure of the...
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DEVIL PHYSICSTHE BADDEST CLASS ON
CAMPUSIB PHYSICS
TSOKOS OPTION I-1THE EAR AND HEARING
IB Assessment StatementsOption 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 StatementsOption 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 StatementsOption I-1, The Ear and Hearing:I.1.8.Solve problems involving intensity
levels.I.1.9.Describe the effects on hearing of
short-term 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
cZ
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 (Weber-Fechner 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
Hzc
f
xL
3036112.0
340
112.0028.044
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
40
5.40
0
1016.3
10
log10
45
xxII
xII
I
I
dB
Audiogram
Steep curve Large high
frequency loss indicates damage due to over-exposure
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 StatementsOption 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 StatementsOption 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 StatementsOption I-1, The Ear and Hearing:I.1.8.Solve problems involving intensity
levels.I.1.9.Describe the effects on hearing of
short-term 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
#1-9
Homework
STOPPED HERE ON 4/4/2013