PHY C15: Stationary Waves (Intro)

Now we’re covering:

  • Stationary Waves
  • Formation of Stationary Waves
  • Difference between Stationary & Progressive Waves

Let’s go!

What is a Stationary Wave?
A wave where the position of the crests & troughs do not move.

They are also called STANDING WAVES.

How are stationary waves formed?

Image result for stationary waves gif
Blue & Red waves are the incident waves travelling past each other in opposite directions.
The black wave is the resultant stationary wave.
2 waves of equal frequency & amplitude travel along the same line at the same speed but in opposite directions
The 2 waves interfere
At certain frequencies called resonant frequencies (fn), the waves interfere to create a wave pattern where the positions of crests & troughs do not move

Parts of Stationary Waves:

NodesPoints with no vibration/amplitude (0 displacement)  
AntinodesPoints with maximum vibration/amplitude (maximum displacement)  

Demonstrating Stationary Waves
Stationary waves can be created either by sending 2 identical waves towards each other, OR by reflecting a wave back in the same direction it came from.

animation showng standing wave resulting from two oppositely directed sine waves
Stationary waves formed by 2 incident waves
By Dan Russell
Image result for stationary waves reflect gif
Stationary wave formed by reflection
By Dan Russell

Stationary waves can form from transverse OR longitudinal waves:

TransverseAntinodes = points of maximum displacement perpendicular to centre line Nodes = points of 0 displacement
Image result for stationary waves reflect gif
LongitudinalAntinodes = points of maximum compression/rarefaction Nodes = points of 0 displacement
Image result for stationary waves reflect gif
By Dan Russell

A few examples in different mediums:

WaterImage result for stationary waves water gif 
String Image result for stationary waves string gif
Sound Image result for stationary waves reflect gif

What are the differences between stationary waves & progressive waves?

Stationary WavesProgressive Waves
Amplitude of vibration varies with positionAmplitude of vibration is the same at every position
Nodes & antinodes do not move along waveCrests & troughs move along wave
Between adjacent nodes, all points vibrate in phasePhase varies continuously along wave
Only certain frequencies can result in stationary waves, depending on the length of string & the speed of the wave (see here)All frequencies can support progressive waves

Next, we’ll see how the frequency affects the formation of stationary waves, as well as the relationship between the length of a tube/string & the allowed frequencies.

⇐ Previous in Physics: Superposition
⇒ Next in Physics: Stationary Waves in Strings & Air Columns

One thought on “PHY C15: Stationary Waves (Intro)

  1. Pingback: 15. Superposition – ProDuckThieves

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