FSKS 123: Chapter 17 (Superposition)

The drawing shows four moving pulses. Although shown as separated, the four pulses exactly overlap each other at the instant shown.

Which combination of these pulses would produce a resultant pulse with the highest peak and the deepest valley at this instant?

• 1 and 2

• 2,3 and 4

• 2 and 3

• 1 and 3

Answer explanation

2 and 3 combine to give a peak of 4 units high and 2 units deep. No other combination gives greater values

Two sounds interacting produces a louder sound when the path length difference between the speakers and the listener is ​ (a)   wavelengths. This process is known as ​ (b)  

• 1,2,3,...
• 0.5, 1.5, 2.5,...
• constructive interference
• destructive interference
• diffraction
• refraction

Two sounds interacting produces a no sound when the path length difference between the speakers and the listener is ​ ​ (a)   wavelengths. This process is known as ​ ​ (b)  

• constructive interference
• 0.5, 1.5, 2.5,...
• destructive interference
• 1.0, 2.0 , 3.0, ....
• diffraction
• refraction

Two birds generate identical 343Hz sound waves which arrive at a person's ear after traveling 2.0 m and 2.5 m, respectively. The speed of sound in air is 343m/s.

Describe the sound heard by the person.

• Same as the original sound

• Louder sound

• No sound

• Softer than original sound, but not zero sound

Answer explanation

Answer explanation

A young boy stands in a 3.5 m wide alley between two very tall buildings and shouts to a friend standing 15 m in front of one of the buildings and 5.0 m to the side of the alley. The boy will hear sounds that travel at an angle of ​​ ​ (a)   degrees

At this angle, what sound frequencies will the second boy hear?

​ (b)   ​

The speed of sound in air v=343 m/s

• 379 Hz

• 310 Hz
• 1087 Hz
• 1.10 Hz

Answer explanation

What must be the diameter D of a circular speaker to produce a 15kHz tone with a diffraction angle of 35°

• 0.05 m

• 50 m

• 0.04 m

• 31 905 m

• 26 151 m

Answer explanation

Answer explanation

The difference between the wavelengths in these 2 combinations give frequency of the beat, 40 Hz

80 Hz - 40 Hz = 40 Hz

60 Hz - 20 Hz = 40 Hz

Reorder the following from lowest frequency to the highest frequency standing waves

• 
• 
• 
• 

A 1.5 m long string, fixed at both ends, has a fundamental frequency of 120 Hz. What is the speed of waves traveling on the string?

• 40 m/s

• 80 m/s

• 180 m/s

• 360 m/s

Answer explanation