The ear drum has an area of 55 mm2 and the oval window has an area of 3.2 mm2…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
The ear drum has an area of mm2 and the oval window has an area of mm2. These are standard values that NCERT does not give. The lever action of the ossicles multiplies the force by .
- What is the ratio of the area of the drum to the area of the window?
- By what factor does the pressure rise from the drum to the window?
- What is this gain in decibels? Use of the pressure ratio.
Need a reminder? The key ideaShow
Sound goes from the pinna and the canal to the ear drum, then through the malleus, incus and stapes to the oval window. Then it goes through the cochlear fluid to the basilar membrane and the hair cells of the organ of Corti. The auditory nerve takes the impulses to the brain. Pressure is force divided by area, and a gain in decibels is of the pressure ratio.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Areas: mm2 and mm2. Lever: .
Plan. Use the ratio of the areas, then the lever, then the decibel formula.
Step 1. The areas. .
Step 2. The gain. .
Step 3. Decibels. dB.
Answer: ; ; dB.
Check. A gain of about times is about dB, since .
Watch out. The areas are in the ratio drum to window. The pressure gain uses the same ratio, because a smaller area gives a larger pressure.
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