Physics - Standing Waves
OCR A-Level Physics 2022
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Flashcards
Formation of a standing wave
When is a standing wave formed?
When two waves with the same frequency and amplitude travelling in opposite directions are superimposed.
What are the points of total constructive interference in a standing wave called?
Antinodes.
What are the points of total destructive interference in a standing wave called?
Nodes.
What is the separation between adjacent nodes or antinodes in a standing wave?
How much energy transfer is there in a standing wave?
None, since the waves making it are travelling in opposite directions.
Microwave standing waves
How can you form a standing wave using microwaves?
Reflect microwaves from a microwave transmitter off a metal plate some multiple of the wavelength away.
Why are waves closer to the metal plate better at creating total nodes in a microwave standing-wave experiment?
Because there is the smallest difference in distance travelled and therefore smallest difference in amplitude.
Phase within a standing wave
What is the phase difference for each point on the trough of a standing wave?
They are in phase.
What is the phase difference for each point on the peak of a standing wave?
They are in phase.
Standing waves on a string
Fundamental mode and harmonics
What is the fundamental mode of vibration of a string?
The simplest standing wave that can be formed by progressive waves travelling along the string.
What is the fundamental frequency of a string?
The frequency of the progressive wave that forms the simplest standing wave on a string.
What’s the frequency of the 1st harmonic in terms of the fundamental frequency $f _ 0$?
What’s the frequency of the 2nd harmonic in terms of the fundamental frequency $f _ 0$?
What’s the frequency of the 5th harmonic in terms of the fundamental frequency $f _ 0$?
Speed of progressive waves
Why is the speed of sound greater at night time?
The speed of sound is temperature dependent.
What is true about the speed of progressive waves along a string at fixed tension?
It is constant.
Boundary conditions and tube ends
When might the wavelength of the fundamental mode/first harmonic in a stationary wave be $\frac{\lambda}{4}$?
When the stationary wave is formed in a closed tube.
What two situations might mean the wavelength of the fundamental mode/first harmonic in a stationary wave is $\frac{\lambda}{2}$?
When the stationary wave is formed on a fixed string or an open tube.
What do you find at the ends of an open tube when forming a stationary wave?
Antinodes.
What is the formula for the fundamental mode of a string with length $L$, tension $T$ and mass per unit length $\mu$?
Nodes and antinodes at boundaries
What are at both ends of a standing wave present on a string fixed at both ends?
Nodes.
What are at either ends of a standing wave present on a string fixed at one end?
- Fixed: Node
- Open: Antinode
What are at either ends of a standing wave present on a pipe with one closed end?
- Closed: Node
- Open: Antinode.