Waves

standing wave

What is a Beat / Beat Frequency

A beat is an interference pattern that is created when two sound waves are at slightly different frequencies

Beat Frequency

difference in frequency between two waves

Constructive Interference (peaks)

waves meet and combine while being in phase

Destructive interference (trough)

waves meet in different places causing them to cancel out (assuming equal amplitude)

Partial destructive interference

two overlapping waves that are out of phase leave behind a smaller wave

How do you know if the sound waves are in tune

When no beat is heard

When in phase are beats quiet or loud

loud

When out of phase are beats quiet or loud

quiet

Frequency Increase means Wavelength

Decrease

Frequency Increase means Wavelength

Decrease

Higher frequency means high or low pitch

high pitch

lower frequecy means high or low pitch

low pitch

dense strings have higher or lower frequencies

lower frequencies

Thin strings have high or low frequencies

high frequencies

applying tension to a string increase or decrease frequency

increases frequency

removing tension from a string increase or decrease frequency

decrease frequency

Doppler Effect

Change in wave frequency due to the relative motion between the observer and the source

as the source of sound comes towards the observer pitch….

increases

as the source of sound goes past the observer pitch…

decreases

the person travelling with the source of sound will hear a change in pitch/frequency or no

No

Closed pipe ½ or ¼ “A pipe closed at one end and open at the other”

¼

Open pipe ½ or ¼ “A pipe is open on both ends”

½

Standing Wave

two identical waves of the same frequency and amplitude travel in opposite directions and interfere with eachother

Which harmonic is the loudest

1st Harmonic

Harmonics become quieter as the number decreases (e.g 1st loudest 2nd quieter then so on)

yes

Harmonics become louder as the number increases (e.g., the 1st is the quietest, the 2nd louder, and so on)

no

How are Harmonics formed in strings

Harmonics are formed in strings when a string is vibrated causing multiple standing waves to be created simultaneously

What is a Node

a node is a fixed point on a stading wave where displacement is zero

What is an Antinode

a antinode is a point of maximum displacement where the medium oscillates back and forth with the greatest amplitude

How are standing waves in strings created

Vibrations travel down the string and are reflected at the fixed ends. The reflected wave interferes with the incident wave to produce nodes (destructive) and antinodes (constructive). Only wavelengths that fit the string with nodes at both fixed ends resonate to form a standing wave.

Formula to find string length

nh x ½ = L

Formula to find Wavelength in strings

2 / nh x L = wavelength

When source frequency approaches the observer in the doppler formula is it (+) or (-)

(-)

When source frequency moves away from the observer in the doppler formula is it (+) or (-)

(+)

Formula to calculate wavelength in a open pipe system (open at both ends)

wavelength = 2L / nH

Formula to calculate wavelength in a closed pipe system

wavelength = 4L / nH

Formula to calculate pipe length in an open system using frequency and sound

L = nH x Vs / 2 x f

Formula to calculate length in a open system using wavelength

L = nH x wavelength / 2

Formula to calculate pipe length in a closed system using frequency and sound

L = nH x vs / 4 x f

Formula to calculate pipe length in a closed system using wavelength

L = nH x wavelength / 4

Are open pipe harmonics nodes or antinodes at each end

antinodes

Are string harmonics nodes or antinodes at each end

nodes

Closed pipe harmonics are only even

no

Closed pipe harmonics are only odd

yes

Closed pipe harmonics are even and odd

no

String harmonics are only even

no

String harmonics can be even and odd

yes

How are harmonics formed in pipes

Harmonics are formed in pipes when the air is vibrated causing multiple standing waves to be created as the sound waves reflect off the pipes ends

Are closed pipe harmonics (open one end closed other) antinodes or nodes

node at one end antinode at the other end

Why cant closed pipe systems produce even harmonics

A closed end creates a node (180° phase shift) and an open end creates an antinode. Because even harmonics require matching boundary conditions at both ends, a pipe closed at only one end cannot produce even harmonics.

As waves travel down the pipe what happens when they get to the end

They reflect off the closed end and experience a 180 degree phase change and due to the incident and reflected wave being out of phase a node is formed

How are standing waves in open pipes created

Vibrations travel down the pipe and are reflected at the open ends. The reflected wave interferes with the incident wave to produce nodes (destructive) and antinodes (constructive). Only wavelengths that fit the pipe with antinodes at both open ends resonate to form a standing wave.

How are standing waves in closed pipes created (closed at one end)

Vibrations travel down the pipe and are reflected at the closed end. The reflected wave interferes with the incident wave to produce nodes (destructive) and antinodes (constructive). Only wavelengths that fit the pipe with a node at the closed end and an antinode at the open end resonate to form a standing wave.