Waves: Topic 4.5 Standing Waves

Question 1

What are standing waves

Answer 1

Standing waves are produced by the amplitude travelling in opposite directions
This is usually achieved when a travelling wave superimposes its reflection
The superposition produces a wave pattern where the crests and troughs do not move

Question 2

Explain how standing waves are formed

Answer 2

Standing waves are formed from the principle of superposition. This is when:
Two waves travelling in opposite directions along the same line with the same frequency superpose

The waves must have:
The same wavelength
A similar amplitude
As a result of superposition, a resultant wave is produced

Question 3

A standing wave is made up nodes and antinodes

Answer 3

Nodes are locations of zero amplitude and they are separated by half a wavelength (λ/2)
Antinodes are locations of maximum amplitude
The nodes and antinodes do not move along the wave
Nodes are fixed and antinodes only oscillate in the vertical direction

Question 4

The Formation of Nodes and Antinodes

Answer 4

Nodes are formed as a result of destructive interference
The amplitude of both waves cancel out, because At the nodes:

The waves are in anti-phase meaning destructive interference occurs
This causes the two waves to cancel each other out

Antinodes are formed as a result of constructive interference
The amplitude of both waves add together, because At the antinodes:

The waves are in phase meaning constructive interference occurs
This causes the waves to add together

Question 5

Explain formation of in phase and anti phase in a standing wave

Answer 5

Points that have an odd number of nodes between them are in anti-phase
Points that have an even number of nodes between them are in phase
All points within a “loop” are in phase

Question 6

The number of nodes and antinodes that fit within the available length of medium depends on:

Answer 6

Stationary waves can form on strings or in pipes
In both cases, progressive waves travel in a medium (i.e. the string or air) and superimpose with their reflections
The frequency of the progressive waves
The boundary conditions (i.e. whether the progressive waves travel between two fixed ends, two free ends or a fixed and a free end)