Bonjour,
a) I = I₀ ⇒ L = 10log(I/I₀) = 10log(1) = 0 dB
b) I = Im = 10 W.m⁻² ⇒ L = 10log(10/10⁻¹²) = 10log(10¹²) = 10 x 12 = 120 dB
c) P = 1,50 W et S = 30 m²
⇒ I = P/S = 1,50/30 = 5,0.10⁻² W.m⁻²
d) P = 5,0.10⁻² W.m⁻²
I = P/S = P/4πR²
e) L = 10log(I/I₀) = 10log(P/(I₀ x 4πR²)
f) R = 1 km = 10³ m
⇒ L = 10log(5,0.10⁻²/(10⁻¹² x 4π x 10⁶) = 36 dB, donc audible
R = 10 km = 10⁴ m
⇒ L = 10log(5,0.10⁻²/(10⁻¹² x 4π x 10⁸) = 16 dB, donc audible