Module 4 Standing Waves

Question 1

What is a standing wave?

Answer 1

are produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions. This is usually achieved by a travelling wave being reflected

Question 2

How can standing waves be created?

Answer 2

reflecting an existing progressive wave (could be set up by plucking a string)

the superposition of two waves with the same frequency and amplitude that travel in opposite directions

resulting in a standing wave with nodes and antinodes

Question 3

Main difference between progressive waves and standing waves?

Answer 3

standing waves store energy, progressive waves transfer energy

Question 4

What two apparatus must be used to generate sound waves?

Answer 4

Signal generator
Loudspeaker

Question 5

What is needed for a standing wave to be produced?

Answer 5

a progressive wave must be reflected,
reflected wave is coherent,
the waves superpose/interfere creating a standing wave.

Must have the same frequency, amplitude, wavelength, speed (coherent), and must be traveling in opposite directions

Question 6

What is a node?

Answer 6

Where the two waves in a standing wave are equal and opposite, they undergo superposition and undergo destructive interference.

This creates a node which is point of minimum amplitude

Question 7

What is an antinode?

Answer 7

points in a standing wave where the waves undergo superposition and interfere constructively, doubling the displacement

This results in an antinode which is a point of max amplitude

Question 8

What is the distance between two adjacent nodes?

Answer 8

1/2 wavelength

Question 9

Compare progressive and standing waves (energy)

Answer 9

Progressive waves transfer energy in the direction of the wave vs standing waves where energy is trapped between the source and the reflector
in a progressive wave.

Question 10

Compare progressive and standing waves (wavelength)

Answer 10

the wavelength is the minimum distance between two adjacent points in phase, in a standing wave the wavelength is twice the distance between adjacent nodes or antinodes

Question 11

Compare progressive and standing waves (phase)

Answer 11

In a progressive wave the phase changes across the full cycle of the wave - in a standing wave particles between adjacent nodes are in phase, particles between opposite sides of a node are in antiphase

Question 12

Compare progressive and standing waves (Amplitude)

Answer 12

In a progressive wave the amplitude is the same for all particles, in a standing wave the amplitude varies for each particle (zero at the node and max at antinode)

Question 13

Explain how nodes are formed

Answer 13

waves travelling in opposite directions meet in antiphase and undergo destructive interference

Question 14

Explain how antinodes are formed

Answer 14

waves travelling in opposite directions meet in phase undergo constructive interference

Question 15

Why can phase difference be described as being either 0 or 180º in a standing wave

Answer 15

particles moving up (or down) together are trapped between two nodes, the phase difference is 0º. All the particles move in the same direction at the same time.

particles either side of a node are travelling in opposite directions so the phase difference is 180º

Question 16

How to start a wave on a string?

Answer 16

pluck the string

Question 17

Describe and explain how to set up a standing wave on a string?

Answer 17

add a frequency generator to a motor

attach to a string with a pully and a weight at it’s other end
(wave speed is constant is same weight on end of same string)

vibrations produce a progressive wave

progressive wave travels along the rope and is reflected by the pully

outgoing and reflected waves interfere and undergo superposition

adjust frequency on the dial until it nodes and antinodes can be seen

Question 18

What is the fundamental frequency/mode?

Answer 18

the lowest possible frequency a standing wave will occurs (that can fit on a string or wire)

Question 19

What are harmonics?

Answer 19

whole number multiples of the fundamental frequency

Question 20

What factors effect at which frequencies do harmonics occur on a string?

Answer 20

tension

mass per unit of length

length of the string

Question 21

On a pipe with one closed end, how many wavelengths are present in the fundamental mode?

Answer 21

1/4wavelength

Question 22

Where are the nodes in the fundamental mode of a standing wave in a closed ended pipe at the fundamental frequency?

Answer 22

node at the closed end

only one node for fundamental frequency in a pipe with one closed end

Question 23

Using a closed ended tube of same length, what is the frequency of the wave in the second harmonic when compared to the fundamental mode?

Answer 23

3f

f is the fundamental frequency

Question 24

What is the wavelength of a standing wave in an open ended pipe at its fundamental mode?

Answer 24

2L

Question 25

Where are the nodes in the fundamental mode of a standing wave in a open ended pipe in the fundamental frequency?

Answer 25

at the centre of the pipe

each open end has an antinode

Question 26

Where are the antinodes in a standing wave formed in an open ended pipe?

Answer 26

at both ends

Question 27

Using a open ended tube of same length, what is the frequency of the wave in the second harmonic when compared to the fundamental?

Answer 27

2f

Question 28

How to find the speed of sound in air using a column of water and a tuning fork?

Answer 28

fill a column with water and strike a tuning fork above the open end

lower the water level until the fundamental mode can be heard (sound gets louder),

record the length of the column

repeat until the length of the wave for the third harmonic is found then use this to find the wavelength

then use the wave equation to find the speed of air in sound using the frequency of the tuning fork v = f x wavelength