(Multiple choice)

(1) True / False

(a) The waves from two coherent sources that are radiating in phase interfere constructively everywhere in space. 

(b) Two wave sources that are out of phase by 180° are incoherent. 

(c) Interference patterns are observed only for coherent sources.

(2)

Beats are produced by the superposition of two harmonic waves only if 

(a) Their amplitudes and frequencies are equal. 

(b) Their amplitudes are the same but their frequencies differ slightly. 

(c) Their frequencies differ slightly even if their amplitudes are not equal. 

(d) Their frequencies are equal but their amplitudes differ slightly.

(3) True or false:

The beat frequency between two sound waves of nearly equal frequencies equals the difference in the frequencies of the individual sound waves.

(4) True or false: 

(a) The frequency of the third harmonic is three times that of the first harmonic. 

(b) The frequency of the fifth harmonic is five times that of the fundamental. 

(c) In a pipe that is open at one end and closed at the other, the even harmonics are not excited.

(5)

Standing waves result from the superposition of two waves of 

(a) The same amplitude, frequency, and direction of propagation. 

(b) The same amplitude and frequency and opposite directions of propagation. 

(c) The same amplitude, slightly different frequency, and the same direction of propagation. 

(d) The same amplitude, slightly different frequency, and opposite directions of propagation.

(6)

An organ pipe open at both ends has a fundamental frequency of 400 Hz. If one end of this pipe is now closed, the fundamental frequency will be 

(a) 200 Hz. 

(b) 400 Hz. 

(c) 546 Hz. 

(d) 800 Hz.

(7)

A string fixed at both ends resonates at a fundamental frequency of 180 Hz. Which of the following will reduce the fundamental frequency to 90 Hz? 

(a) Double the tension and double the length. 

(b) Halve the tension and keep the length fixed. 

(c) Keep the tension fixed and double the length. 

(d) Keep the tension fixed and halve the length.

(8)

When the tension on a piano wire is increased, which of the following occurs? 

(a) Its wavelength decreases. 

(b) Its wavelength remains the same while its frequency increases. 

(c) Its wavelength and frequency increase. 

(d) None of the above.