The professor once again returns the apparatus to its original setting, but now she adjusts the oscillator to produce sound waves of half the original frequency. What happens?

(a) The students who originally heard a loud tone again hear a loud tone, and the students who originally heard nothing still hear nothing. 

(b) The students who originally heard a loud tone now hear nothing, and the students who originally heard nothing now hear a loud tone.

(c) Some of the students who originally heard a loud tone again hear a loud tone, but others in that group now hear nothing.

(d) Among the students who originally heard nothing, some still hear nothing but others now hear a loud tone.

Interference occurs with not only light waves but also all frequencies of electromagnetic waves and all other types of waves, such as sound and water waves. Suppose that your physics professor sets up two sound speakers in the front of your classroom and uses an electronic oscillator to produce sound waves of a single frequency. When she turns the oscillator on (take this to be its original setting), you and many students hear a loud tone while other students hear nothing. (The speed of sound in air is 340 m/s.)