today’s topic: constructive and destructive interference learning goal: swbat predict the outcomes...
TRANSCRIPT
Today’s Topic: Constructive and Destructive Interference
Learning Goal:
SWBAT predict the outcomes of two incoming waves.
With Words and with a Drawing:What would a large amplitude and low frequency
light wave look like?
What would a small amplitude and high frequency light wave look like?
HomeworkDue Wednesday, 6/3:Complete the Wave Speed Worksheet
Two Days Late:Pendulum Lab Simple Harmonic Motion Worksheet
RecapWhat does a transverse wave look like?
If you had a slinky, how would you make a transverse wave?Which way would the wave travel?
What are some examples of transverse waves?
RecapWhat does a longitudinal wave look like?
If you had a slinky, how would you make a longitudinal wave?Which way would the wave travel?
What are some examples of longitudinal waves?
InterferenceWaves are different from other types of
things we deal with on a day-to-day basis.
For example, let’s say I want to take two Physics books and combine them into each other, so they both occupy the same space at the same time.
Meaning…
Wave InterferenceI want both books to overlap each other:
We can’t do this, can we?
But what about waves?
Can we overlap sound waves over each other?
Yes! We all do it all the time!
Wave InterferenceWaves, unlike objects made of matter
(rocks, tables, etc.) can exist at the same time in the same place.
This is because waves are a disturbance in a medium – they are not made of matter.
SuperpositionWhat we are seeing with that
demonstration is an example of superposition.
Superposition: The combination of two overlapping waves.
Overlapping Waves
If we look close enough at this picture, we can see certain areas where the waves seem to interfere with one another.
Overlapping WavesThese waves superimpose onto one
another creating an interference pattern.
An interference pattern is a regular arrangement of places where wave effects are increased, decreased, or neutralized.
The net displacement (amplitudes) are added together resulting in different interference.
Types of InterferenceLet’s pump the brakes.
Imagine we have two crests coming towards each other like so:
What will happen when these waves interfere and superimpose onto each other?
Types of InterferenceThe resulting wave (in green) is taller
than the two original waves:
The same can happen with two troughs come together:
Constructive InterferenceThis is an example of constructive
interference.
In constructive interference, the crest of one wave overlaps with the crest of another and their individual effects add together. The result is a wave of increased amplitude.
Types of InterferenceWhat if we have the following situation:
Predict what will happen in this case.
This is destructive interference.
Destructive InterferenceIn destructive interference, the crest of
one wave overlaps with the trough of another and their individual effects are reduced. The high part of one wave simply fill in the lowpart of another.
The result is a waveof a reduced amplitude.
Destructive Interference
These “spokes” you see here in the ripple tank are locations of where there is destructive interference.
Let’s highlight them.
Types of InterferenceWhat about in this situation?
Predict what will happen in this case.
This is complete destructive interference.
Complete Destructive Interference
In complete destructive interference, the instant the two pulses overlap, they completely cancel each other; it is as ifthere is no disturbanceat all.