Flashcards in 4.9 Standing Waves Deck (19):
When is standing wave formed?
When two identical travelling waves moving in opposite directions meet and superpose.
What is important about a standing wave?
Only the amplitude changes, the pattern does not move.
What is important about a standing wave on a string?
If the string is fixed at both ends these are nodes on the standing wave.
What is the first harmonic?
When the entire string is occupied by one half wave
lambda 1 = 2L
What is the second harmonic?
When the entire string is occupied by two half waves
lambda 2 = L
What is the third harmonic?
When the entire string is occupied by three half waves
lambda 3 = 2L/3
What important about each of these standing waves?
They each have a unique frequency.
How can we create a particular harmonic?
Vibrate the string up and down with its associated frequency - creates a travelling wave on the string which upon reflection form the fixed end creates a second travelling wave in the opposite direction.
How can a standing wave be set up in open ended pipes?
A traveling wave sent down the pipe will reflect form the ends even though they are open so we have condition for the formation of a standing wave.
Where are the nodes and antinodes on a standing wave in open ended pipes?
Molecules at the ends of the pipe vibrate the most so they are antinodes, the molecules in the middle do not oscillator at all so they are a node.
What is the first harmonic for open ended pipes?
lamba 1 = 2L
What is the second harmonic for open ended pipes?
lambda 2 = L
What happens if the pipe has one end closed?
The standing wave will have a node at the closed end and an antinode at the open end.
What is the first harmonic for a pipe with one end closed and one end open?
One quarter wavelength filled the pipe
lambda 1 = 4L
What is the third harmonic for a pipe with one end closed and one end open?
Three quarter wavelength filled the pipe
lambda 3 = 4L/3
What is important about harmonic for pipes where one end is closed?
Only odd number harmonics are possible.
What is the difference in energy between standing and travelling waves?
Travelling waves transfer energy, standing waves do not.
What is the difference in amplitude between standing and travelling waves?
Travelling waves have constant amplitude, standing waves do not.