8.2: Measuring Mechanical Waves

Question 1

Displacement-Distance Graphs

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Answer 1

• Shows the displacement of all particles along the length of a transverse wave at a particular time
• The amplitude of a wave is the maximum displacement of a particle from the average position. Total distance a particle will move through in one cycle is twice the amplitude
• The wavelength of a wave is the distance between any two sucessive points
• Two particles on the wave are said to be in phase, if they have the same displacement from the average position

Question 2

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Frequency (f)

Answer 2

Frequency is the number of complete cycles that pass a given point per second, measured in Hertz (Hz)

Question 3

Displacement-Time Graphs

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Answer 3

• Amplitude is still the maximum displacement from the average position
• However, distance between two sucessive points in a phase in a displacement-time graph represents the period of the wave (T), measured in seconds
• Period is the time it takes for any point on the wave to go through one complete cycle, period of a wave is inversely proportional to frequency:
• T = 1/f, where T is the period of wave (s), f is the frequency (Hz)
• Amplitude and period of a wave, direction of motion of a particular particle can be determined from a displacement-time graph

Question 4

The Wave Equation

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Answer 4

Question 5

What is the Doppler Effect

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Answer 5

• Suppose an ambulance siren is stationary relative to an observer, who will receive the compressions and rarefactions at the same rate as the source creates them. If the source were to travel towards the observer, the consecutive disturbances will move closer together. The disturbance will have less distance to travel before reaching the observer in comparison to the one before it. The frequency of arrival of the disturbances is higher than the originating frequency.

Question 6

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Doppler effect example

Answer 6

• An object emitting a sound and moving towards an observer will emit the sound waves closer together in the direction of travel, thus, a higher frequency is heard by the observer.
• When the object is moving away from the observer, the sound waves are emitted further apart, a lower frequency is heard.