Explanation:
Given that,
Distance 1, r = 100 m
Intensity, [tex]I_1=1.24\times 10^{-8}\ W/m^2[/tex]
If distance 2, r' = 25 m
We need to find the intensity and the intensity level at 25 meters. Intensity and a distance r is given by :
[tex]I=\dfrac{P}{4\pi r^2}[/tex].........(1)
Let I' is the intensity at r'. So,
[tex]I'=\dfrac{P}{4\pi r'^2}[/tex]............(2)
From equation (1) and (2) :
[tex]I'=\dfrac{Ir}{r'^2}[/tex]
[tex]I'=\dfrac{1.24\times 10^{-8}\times 100}{25^2}[/tex]
[tex]I'=1.98\times 10^{-9}\ W/m^2[/tex]
Intensity level is given by :
[tex]dB=10\ log(\dfrac{I'}{I_o})[/tex], [tex]I_o=10^{-12}\ W/m^2[/tex]
[tex]dB=10\ log(\dfrac{1.98\times 10^{-9}}{10^{-12}})[/tex]
dB = 32.96 dB
Hence, this is the required solution.
