Level of sound is related to intensity by this equation
[tex]L = 10 Log \frac{I}{I_o}[/tex]
given that
L = 85 dB
also we know that
[tex]I_o = 10^{-12} W/m^2[/tex]
now we have
[tex]85 = 10 Log \frac{I}{10^{-12}}[/tex]
By solving above equation
[tex]I = 10^{8.5} * 10^{-12}[/tex]
[tex]I = 3.16 * 10^{-4} W/m^2[/tex]
now above is the intensity due to two firecrackers and if we wish to find the sound level of one firecracker then we will find its half level intensity
[tex]I_1 = \frac{I}{2}[/tex]
[tex]I_1 = 1.58 * 10^{-4}[/tex]
now again by above formula
[tex]L = 10 Log \frac{1.58 * 10^{-4}}{10^{-12}}[/tex]
[tex]L = 82 dB[/tex]
