SPH3UI Waves and Sound Practice Test

Water waves strike a dock so that the entire straight wave front hits the dock at the same time. A person sitting on the dock observes that the water repeats the cycle of moving up and down against the dock, through a distance of 40 cm, every 2.0 seconds. The distance between any two peaks is about 1.4 m
State the following characteristics of the wave (include units). (4)
Frequency - 0.5 Hz
Period – 2 s
Amplitude – 10 cm
Wavelength – 1.4 m
Use this information to calculate the speed of the water waves. (2)

v = 0.70 m/s

The reflected waves interfere with the incoming waves to produce a standing wave. Why is this name appropriate? (1)

Name is appropriate b/c it doesn’t look like the wave travels to the left or right…it looks like it’s “standing” in place. Each crest becomes a trough and vice versa.

The nodes of the standing wave are caused by destructive interference. Explain. Destructive interference results in nodes b/c crests are cancelled by troughs and vice versa.

What happens when 2 billiard balls, rolling towards one another, collide head on? How does this differ from 2 waves or pulses that collide head on?

On a hot 280C day, a BCI student chats with friends out on the upper playing field 100 m from the outside loudspeaker. The student suddenly hears the buzzer to end the lunch period.
At what speed does sound travel in air at this temperature? (2)

v = 348 m/s

How much time was required for the sound to reach the student’s ears? (2)

t = 0.29 s

Draw the resultant displacement of the medium caused by the heavy and light pulses in the diagram below. (3)

Make a sketch illustrating the Doppler effect. Use the sketch to illustrate the effect on the frequency of the sound heard by an observer if the source of the sound is moving towards the observer. (4)

- sketch should show compressed waves that are closest to observer so that the observer hears high pitch/loud sound (b/c of small wavelength).

An organ tuner is tuning an organ pipe to a frequency 440 Hz. A 440 Hz tuning fork is at the same time as the organ pipe and 2 beats per second are heard.
What are beats and why are beats produced? (2)

-Beats are characterized by loud then quiet sounds. They occur b/c of constructive and destructive interference of 2 frequencies (2 waves of different frequencies). The constructive interference makes a loud sound and the destructive interference is quiet (node).

What are the possible frequencies of the organ pipe? (2) 438 Hz and 442 Hz

Use the diagram below to explain the production of an interference pattern. Label the lines in the drawing. Identify nodal lines and explain the meaning and origin of nodal lines.

An air column open at both ends is 360 cm long. It is made to vibrate in the second resonance mode.

Make a labelled sketch of the vibration that is occurring in the tube. (3)

-open ended air column that is 360 cm long (label), 2 nodes, wavelength = 0.360 m.

If the speed of sound is 344 m/s, what is the frequency of the sound produced? (3) f = 956 Hz

For a track race, the starter at the starting line is 100 m from the finish line (where the timers are). Instead of following instructions to start the watch when the flash of the gun is seen, the timer in lane 4 starts the watch when the sound of the gun is heard. If the air temperature is 27.0 oC, by how much is the time recorded by the lane 4 timer incorrect? Is the recorded time to low or too high? Explain. (5)

-recorded time is too low gives the runner a faster time than what they should have

- time with speed of sound is t = 0.29 s

-time with speed of light is t = 3.3x10-7 s

Why is it necessary for soldiers to march off-step across a bridge? (2)

-to avoid matching the natural frequency of the bridge

-if the natural frequency is met, then the bridge may resonate and eventually crumble