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A chinese fire cracker when busted creates 100 dB sound at a distance of 10 cm. this level of sound is dangerous and can create deafness. To reduce the sound to a safer level, we need to stand far from it. At what minimum destance from the fire cracker a person should stand so that sound level heard by him is 40 dB? (Assume that sound energy spread equally in all directions)A. 100 mB. 6.63 cmC. 10 mD. 1 m |
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Answer» Correct Answer - A Intensity at 10 cm `100=10log(I_(1))/(I_(0))` `impliesI_(1)=10^(-2)=W//m^(2)` Intensity at `r` distance `40=10log(I_(2))/(I_(0))` `impliesI_(2)=10^(-8)W//m^(2)` Since firecracker is a point source: `(I_(1))/(I_(2))=(r_(2)^(2))/(r_(1)^(2))=(r^(2))/((0.1)^(2))` `r=0.1xxsqrt((10^(-2))/(10^(-8)))=100m` |
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