What is coherence?
When two wave sources have the same wavelength, frequency and a fixed phase difference between them.
Superposition is…
When two or more waves pass through each other
Their displacements combine, then they go separate ways.
Name the 2 types of interference
- Constructive
- Destructive
If the waves aren’t the same size, the interference will probably not be noticeable.
Constructive interference?
crest + crest = bigger crest
trough + trough = bigger trough
combine and become one big one basically
Happens when path difference is a whole number of wavelengths.
Destructive interference
crest + trough = nothing
they have to be equal in size
they cancel each other out for a sec
What does “in phase” mean
“in step”; for two waves to be at the same point in their wave cycle.
measured in degrees or radians
What is a Stationary wave?
When two progressive waves with = frequency moving in opposite directions superpose
they transfer no energy
What is meant by “resonant frequency”?
in relation to stationary waves
That at which an exact number of waves is emitted as hits the other end.
these waves are then reflected back, reinforcing each other in a pattern
How to demonstrate stationary waves with micowaves
- Set up a microwave transmitter in front of a metal plate
- Place a probe connected to a loudspeaker in between
- To find the nodes and antinodes, move the probe back and forth
How to show stationary waves in a column of air
- Put powder in the bottom of a glass tube
- Place a loudspeaker at one end
- Soundwaves produced will shake powder away from the antinodes but leave it at the nodes
Which 3 factors affect resonant frequencies of a string?
- Its length - longer = lower freq.
- Its mass - heavier = lower freq
- Tension in it - looser = lower freq
investgate this in req practical
