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# Devil physics The baddest class on campus IB Physics - PowerPoint PPT Presentation

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.

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### Tsokos Option I-1The ear and hearing

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.

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.

Option 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.

• 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

• 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

• 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

• 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

• Cochlea is where hearing takes place

• Vestibular, Helicotrema and Tympanic canals (2cm long)

• Round window is pressure release point

• 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

• Basilar membrane

• Organ of Corti responsible for converting vibrations into electrical signals

• Different parts are sensitive to different frequency ranges

• 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

• 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

• 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

• 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

• 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

• 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

• The normal hearing range is 20 Hz to 20,000 Hz

• The threshold of hearing reduces with age

• 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

• 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

• The length of the ear canal is 2.8 cm

• Subjective

• How high or low a sound is

• Primarily determined by frequency, but also by intensity

• 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

• 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

• Aging

• Gently curved with smaller loss in decibels

• Damage

• More substantial loss, especially in higher frequencies

• Steep curve

• Large high frequency loss indicates damage due to over-exposure

• Aging would show shallow curve, less overall loss

• Circles for air

• Triangles for bone

• Gap between the two indicates a conduction problem in middle or outer ear

• When the bone and air graphs nearly coincide, the problem is most likely a cochlear or nerve problem in the inner ear

• 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

• 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

### Okay, I hear ya!

• 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

• 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

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.

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.

Option 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.

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