STANDING WAVES. Department of Textile The Open University of Sri Lanka. Content. Objectives What is a wave? Principle of superposition Introduction to standing waves Conditions that apply for a standing wave Difference between standing and travelling wave
Department of TextileThe Open University of Sri Lanka
After completing this session you should be able to
explain what a wave is
explain the Principle of superposition
explain how standing waves are
draw the standing waves in closed
pipes, open pipes and strings
Wave is a method of transmitting energy by means of large number of oscillations. Oscillations may be mechanical or electromagnetic.
Have you ever seen a flag on a windy day?
The wind creates waves in the flag. Both the waves in a flag and the ocean are waves that you can see.
When two waves are in phase with each other they add together.
When two waves are 1800 out of phase with each other they will cancel.
(a.) Constructive Interference (b.) Destructive Interference
When two waves of the same frequency moving in opposite directions super impose, produces a standing or stationary wave.
To get an idea about how to form a standing wave, let’s think that a vibration is sent along a string. This may cause to form a wave. This wave will reflect at the other end.
These incidents and reflected waves will superimpose with each other and form a standing wave (Stationary wave).
Both waves should be in the same frequency
The wave length of two waves should be the same
Amplitude must be equal or nearly equal to each other
Should travel in opposite directions
(a.) Standing wave (b.) Travelling wave
When a wave is propagating along a string its linear mass density can be written as follows.
m =Mass of the string
L=Length of the string
=Linear mass density
T= Tension of the string
Velocity depends on both tension and linear density.
The fundamental vibration mode of a stretched string is seen in the figure.
The wavelength is twice the length of the string.
Also in a string
T=Tension of the string
L=Length of the string
Many of the practical applications of stationary waves are found in musical instruments like the flute, trombone and clarinet.
Pipes with two open ends.
As you know already standing waves are formed when two progressive waves of the same medium are moving.
You can see that at the closed end of a tube there must be a node, because air molecules couldn’t vibrate when they contact the wall . Open end should have a antinode since it’s air particles are free to vibrations.
Pipes with one open end.
Published by The Open University of Sri Lanka
Author : Mr. L.S.A.Perera
Web Content Developer : B. Krishni Perera