A pair of in-phase stereo speakers are placed side by side, 0.85 m apart. You stand directly in front of one of the speakers, 1.1 m from the speaker. What is the lowest frequency that will produce constructive interference at your location?

A laser beam is incident on two slits with a separation of 0.205 mm, and a screen is placed 4.95 m from the slits. If the bright interference fringes on the screen are separated by 1.56 cm, what is the wavelength of the laser light? in nanometers.

Two loudspeakers are mounted on a rack, one h = 2.74 m above the other. Exactly 8.00 meters to the right of the midpoint, a microphone rests at point O. Point O is equally distant from each loudspeaker.   The loudspeakers are driven by the same tone generator and vibrate in phase at 390 Hz. It is possible to create a condition of destructive interference at Point O by changing one or both of the path lengths (r1 and r2) between speaker and microphone. Suppose that this is done by raising the upper speaker while leaving the lower speaker in place. What is the smallest vertical distance (in m) that you would need to raise the upper speaker by, in order to create destructive interference at Point O? (The speed of sound waves in air is 343 m/s.)

Two waves travelling in the same direction are given by: y1 = 0.2 sin(2rx-20t+p) and y2 = 0.2 sin(2Ttx-20t), where x and y are in meters and t is in seconds. If the %3D two waves start at the same moment, then the path difference, Ax, corresponding to a fully destructive interference is: