Intensity Optics

Really stuck with this 1st yr optics and physics q pls help?

(a) Calculate the sound level in dB (decibels) of a sound wave that has an intensity of 8.5μW/m2 (1μW = 1 × 10-6 W).
(b) An electric drill has a measured sound level of 66 dB. What is the intensity of this sound in W/m2?
(c) An acoustic experiment in the laboratory requires a sound intensity of 1.2 W/m2 at a distance of 5 m from the output speaker. What power output is required?

a) β = 10dB*log(I/I0) = 10db*log(8.5×10^-6/10^-12) = 69.3dB

b) Again β = 10dB*log(I/I0) so I = I0*10^(β/10) = 10^-12*10^(66/10) = 3.98×10^-6 W/m^2

c) P = I*A = 1.2W/m^2*(4π*r^2) = 1.2*(4π*5^2) = 377W

Intensity. Multiple lenses. Polarization (1)

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