A train sounds its horn as it approaches an intersection. The horn can just be heard at a sound intensity level of 40 dB by an observer (or listener) 4.3 km away. (a) What is the intensity of the horn's sound wave at this location? Recall that a SIL of 0 dB corresponds to an intensity of 110¹² W/m² and that each increase of +10 dB in SIL corresponds to multiplying the intensity by 10. W/m² (b) The sound from the horn is emitted as spherical waves in all directions. That means that at a distance of r away from the horn, the sound wave is spread over the area of the surface of a sphere: Area = 4r². Using this idea, what is the power required to produce this sound wave? W (c) What would the SIL of the horn's sound wave be at a distance of 1.7 km from the train?