A fan at a rock concert is 45.0m from the stage, and at this point the sound int
ID: 2164104 • Letter: A
Question
A fan at a rock concert is 45.0m from the stage, and at this point the sound intensity level is 110dB . Sound is detected when a sound wave causes the tympanic membrane (the eardrum) to vibrate . Typically, the diameter of this membrane is about 8.40mm in humans.How much energy is transferred to her eardrums each second (Answer in micro joules)?
How fast a typical 2.0mg mosquito would have to fly (in mm/s) to have an amount of energy delivered to the eardrum each second when someone whispers (20 dB) a secret in your ear?
Explanation / Answer
The sound travels in all directions .. so it's power is spread out over the surface of a sphere. The radius of this sphere increases as it travels, distributing the power (P) over a greater and greater area (A) that reduces it's intensity (I) in W/m² Intensity, I = P/A .. for a given source power the intensity I ? 1/A ? 1/d² I ? 1/d² .. I1 / I2 = (d2)² / (d1)² Intensity at 30m .. I2 = I1 x (d1)² / (d2)² .. I2 = 0.10W/m² x (1.0m)² / (30.0m)² .. .. I2 = 1.10^-4 (J/s)/m² .. W/m² Energy collected by ear drum each sec .. E = I2 x Ear drum area E = 1.10^-4 (J/s)/m² x (p.[4.20^-3m]²) .. .. .. ?E = 6.10^-9 J
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