= 10 log 0 60 dB = 10 log 10 −12 60 = log 10 10 −12 6 = 60 dB 10 = −12 10 −6 2 = 10 W/m = 50 m ⋯ = 2 4 −6 2 10 W/m = 4(3,14)(50) 2 −6 10 W/m = 2 3,14×10 4 −6 4 2 = 10 log = (10 W/m )3,14 × 10 −2 0 = 3,14 × 10 watt = 4 2 3,14 × 10 −2 watt