We're in class with a SIL decibel meter up front, and everyone is screaming at the top of their lungs, hooting and shouting and pounding on their desks, shooting off firecrackers, its Phys 1240 gone wild...and the meter is reading a reasonably steady sound intensity level of 120 dB. At a pre-arranged signal from Professor Parker, seventy-five (75) percent of the class suddenly gets totally quiet, while the remaining students continue making the same noise. What sound intensity level would the meter now show?
To calculate the new sound intensity level when 75% of the class gets quiet, we need to consider the decrease in sound intensity from those students who stop making noise.
First, let's assume there are 100 students in the class to simplify the calculation. If 75% of the class gets quiet, that means 75 students have stopped making noise, while 25 students continue making the same noise.
To find the new sound intensity level, we need to determine the change in sound intensity caused by the 75 students who stopped making noise.
The sound intensity level is measured in decibels (dB), which is a logarithmic scale. Each 10 dB increase represents a tenfold increase in sound intensity. Conversely, each 10 dB decrease represents a tenfold decrease in sound intensity.
Now, let's assume that each student generates an equal amount of sound intensity, resulting in a combined sound intensity level of 120 dB from all the students. If 100 students generate a sound intensity level of 120 dB, each student would contribute approximately 1.2 dB (120 dB / 100 students) to the total sound intensity.
When 75 students stop making noise, the sound intensity contributed by them decreases. Hence, we subtract their contribution to the total sound intensity. 75 students * 1.2 dB = 90 dB.
Therefore, the sound intensity level shown on the meter would be 120 dB - 90 dB = 30 dB.