Superposition of Pulses Example
Example:
Question
The two pulses shown below approach each other at \(\text{1}\) \(\text{m·s$^{-1}$}\). Draw what the waveform would look like after \(\text{1}\) \(\text{s}\), \(\text{2}\) \(\text{s}\) and \(\text{5}\) \(\text{s}\).
Step 1: After \(\text{1}\) \(\text{s}\)
After \(\text{1}\) \(\text{s}\), pulse A has moved \(\text{1}\) \(\text{m}\) to the right and pulse B has moved \(\text{1}\) \(\text{m}\) to the left.
Step 2: After \(\text{2}\) \(\text{s}\)
After \(\text{1}\) \(\text{s}\) more, pulse A has moved \(\text{1}\) \(\text{m}\) to the right and pulse B has moved \(\text{1}\) \(\text{m}\) to the left.
Step 3: After \(\text{5}\) \(\text{s}\)
After \(\text{5}\) \(\text{s}\) more, pulse A has moved \(\text{5}\) \(\text{m}\) to the right and pulse B has moved \(\text{5}\) \(\text{m}\) to the left.
Optional Experiment: Constructive and destructive interference
Aim
To demonstrate constructive and destructive interference
Apparatus
Ripple tank apparatus
Method
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Set up the ripple tank
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Produce a single pulse and observe what happens (you can do this any means, tapping the water with a finger, dropping a small object into the water, tapping a ruler or even using a electronic vibrator)
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Produce two pulses simultaneously and observe what happens
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Produce two pulses at slightly different times and observe what happens
Results and conclusion
You should observe that when you produce two pulses simultaneously you see them interfere constructively and when you produce two pulses at slightly different times you see them interfere destructively.
This lesson is part of:
Mechanical Waves and Sound