3.3.1.3 - Principle Of Superposition Waves And Formation Of Stationary Waves Flashcards
What is a stationary wave?
The superposition of two waves with the same frequency, moving in opposite directions.
Differences between a progressive wave and a stationary wave?
- No energy is transmitted by a stationary wave.
- All points vibrate at the same amplitude, unlike a progressive wave where the amplitude varies from maximum a the antinodes to zero at the nodes.
How can you generate a stationary wave?
Setting up a driving oscillator at one end of a stretched string with the other end fixed.
What are nodes?
Where the amplitude of the vibration is zero.
What are antinodes?
Points of maximum amplitude.
Describe first harmonic?
1/2 a wavelength and has one loop with a node at each end.
Describe the second harmonic?
Twice the frequency of the 1st harmonic. Two loops with a node at each end and one in the middle. 1 wavelength.
Describe the 3rd harmonic?
Three times the frequency of the first harmonic. 1.5 wavelengths.
In the equation for the first harmonic, what do l, T and u =?
L = length of string (m) T = tension (N) u = mass per unit length (kgm-1)
What else can you form stationary waves using?
Microwaves and sound waves.
How are stationary waves produced using microwaves?
Microwaves are reflected off a metal plate. To find the nodes and antinodes move the probe between the transmitter and reflecting plate.
How are sound waves used to show stationary waves?
Stationary waves are produced in a glass tube. The lycopodium powder laid across the bottom of the tube is shaken away from the antinodes but is left undisturbed at the nodes.
Longer string =
Lower resonant frequency, because half the wavelength of the resonant frequency is longer.
The heavier the string =
The lower resonant frequency because waves travel more slowly down the string.
The looser the string =
The lower the resonant frequency, because waves travel more slowly down a loose string.
