Two sound speakers separated by 100 m face each other and vibrate in unison at a frequency of 85 Hz. The air temperature in the room is controlled at a constant 15 degrees Celsius and the speed of sound in the room is 340 m/s.

a) Calculate the wavelength of the sound waves produced.

b) An observer is placed between the two speakers. When one speaker is turned on the observer detects a certain intensity of the sound wave. When the second speaker is turned on the observer detects an increase in the intensity of the sound. Explain.

c) The observer now walks slowly along the line between the two speakers towards the speaker on the right. As he moves he observes a position where there is no sound intensity detected at all. Explain.

d) Are there other positions on a line between the speakers where the observer would not hear any sound? Explain.