U1-IW1: Two Speakers Emit 300 Hz in Phase. One Speaker Is 10M Away to Your North. The

physics 112 hw26

Due Monday, 24 November 2014

U1-IW1: Two speakers emit 300 Hz in phase. One speaker is 10m away to your north. The second is to your east. How far away is the second if the 300 Hz frequency sounds particularly soft? (There is more than one answer.)

U1-IW2: Two speakers 50 m apart are emitting a 50 Hz frequency in phase. You stand between them. At what distances from the left speaker will this frequency sound particularly loud? How does your answer change if the speakers are exactly 180o out of phase?

U1-I1: (Wolfson, Ch. 14 Prob. 51) The light intensity 3.3m away from a light bulb is 0.73 W/m2. What is the power output of the bulb, assuming it radiates equally in all directions?

U1-I2: (Wolfson, Ch. 14 Prob. 52) Light emerges from a 5.0-mW laser in a beam 1.0mm in diameter. The beam shines on a wall, producing a spot 3.6 cm in diameter on the wall. What are the beam intensities

a) at the laser and

b) on the wall?

U1-I3: (Wolfson, Ch. 14 Prob. 65) Most people will agree that in order for something to sound “twice as loud,” the sound intensity level in dB must go up by 10 dB. Similarly, for something to sound half as loud, its sound intensity level must go down by 10 dB. At a distance 2.0 m from a localized sound source you measure the sound intensity level as 75 dB. How far away must you be for the perceived loudness to drop in half?

U1-D1: (Wolfson, Ch. 14 Ex. 43) The stationary siren on a firehouse is blaring at 85 Hz. What is the frequency perceived by a firefighter racing toward the station at 120 km/h?

U1-D2: (Wolfson, Ch. 14 Ex. 44) A fire truck’s siren at rest wails at 1400 Hz; standing by the roadside as the truck approaches, you hear it at 1600 Hz. How fast is the truck moving? What is the answer if there is a 10m/s wind blowing in the direction the truck is moving?

U1-D3: (Wolfson, Ch. 14 Prob. 69) You’re standing by the roadside as a truck approaches, and you measure the dominant frequency in the truck noise at 1100 Hz. As the truck passes, the frequency drops to 950 Hz. What is the truck’s speed?