4.5- STATIONARY AND PROGRESSIVE WAVES

Question 1

When a guitar string is plucked what is the sound produced dependent on?

Answer 1

way in which string vibrates

Question 2

What happens if a string on a guitar is plucked gently at its centre?

Answer 2

stationary wave of constant frequency set up on string

Question 3

When a string on a guitar is plucked at the centre and a stationary wave of constant frequency is set up, what is the frequency of sound produced like?

Answer 3

sound produced has constant frequency

Question 4

What happens if a guitar string is plucked harshly?

Answer 4

string vibrates in more complicated way + not produced contains other frequencies, as well as frequency produced when plucked gently

Question 5

When is a stationary wave formed?

Answer 5

when two progressive waves pass through each other

Question 6

How can a stationary wave be achieved on a string in tension?

Answer 6

by fixing both ends + making middle part vibrate, so progressive waves travel towards each end, reflect at ends, + then pass through each other

Question 7

What is the simplest stationary wave pattern on a string called?

Answer 7

first harmonic of string

Question 8

What is the first harmonic of a string sometimes referred to as the strings —?

Answer 8

fundamental mode of vibration

Question 9

What does the first harmonic of a string consist of?

Answer 9

single loop that has a node at either end

Question 10

What is a node?

Answer 10

point of no displacement

Question 11

On the first harmonic of a string, where does the string vibrate with maximum amplitude?

Answer 11

midway between the nodes

Question 12

What is the point of the first harmonic of a string where there is maximum amplitude referred to as?

Answer 12

antinode

Question 13

As there are antinodes at the midway of the nodes, how does the string vibrate?

Answer 13

from side to side repeatedly

Question 14

For the first harmonic pattern to occur, what must the distance between the nodes at either end be like?

Answer 14

must be equal to one half-wavelength of waves on string

Question 15

Equation for distance between adjacent nodes?

Answer 15

distance between adjacent nodes = 1/2λ

Question 16

What happens if the frequency of the waves sent along the rope from either end is raised steadily, when the pattern is of a first harmonic?

Answer 16

pattern disappears and new pattern observed with two equal loops along rope

Question 17

What is the new pattern (second harmonic) observed when the frequency is increased like?

Answer 17

has node at centre + at either end

Question 18

When is the new pattern observed when frequency is increased formed?

Answer 18

when frequency twice as high, corresponding to half the previous wavelength

Question 19

What is the distance from one node to the next equal to in the second harmonic?

Answer 19

equal to have a wavelength

Question 20

If the distance from one to the next is equal to half a wavelength in the second harmonic, what is the length of the rope equal to?

Answer 20

equal to one full wavelength

Question 21

What do stationary waves that vibrate freely not do?

Answer 21

stationary waves that vibrate freely do not transfer energy to their surroundings

Question 22

What is the amplitude of vibration at the nodes?

Answer 22

zero

Question 23

As the amplitude of vibration is zero at the nodes, what does this mean?

Answer 23

no energy at the nodes

Question 24

Where is the amplitude of vibration a maximum?

Answer 24

at the antinodes

Question 25

As the amplitude of vibration is a maximum at the antinodes, what does this mean?

Answer 25

maximum energy at antinodes

Question 26

Why is no energy transferred in a vibrating stationary wave pattern?

Answer 26

because nodes + antinodes are at fixed positions

Question 27

What happens when two progressive waves are in phase?

Answer 27

reinforce each other to produce large wave

Question 28

What happens a quarter of cycle when two progressive waves are passing through each other?

Answer 28

two waves have each moved one-quarter of a wavelength in opposite directions- now in antiphase so cancel each other

Question 29

What happens after a further quarter cycle (now half) when two progressive waves are passing through each other?

Answer 29

two waves back in phase. resultant again a large wave, except reversed

Question 30

Are the points where there is no displacement fixed in position throughout? (explanation of stationary waves)

Answer 30

yes

Question 31

What happens between the points of no displacement?

Answer 31

stationary wave oscillates between nodes

Question 32

How does the amplitude of a vibrating particle in a stationary wave pattern vary with position?

Answer 32

from zero at node to maximum amplitude at antinode

Question 33

When is the phase difference between two vibrating particles in a stationary wave zero?

Answer 33

if two particles between adjacent nodes or separated by even number of nodes

Question 34

What is the phase difference between two vibrating particles in a stationary wave 180° (= π radians)?

Answer 34

if two particles separated by odd number of nodes

Question 35

What is the frequency like in stationary waves?

Answer 35

all particles except those at nodes vibrate at same frequency

Question 36

What is the frequency like in progressive waves?

Answer 36

all particles vibrate at same frequency

Question 37

What is the amplitude like in a stationary wave?

Answer 37

amplitude varies from zero at nodes to maximum at nodes

Question 38

What is the amplitude like in a progressive wave?

Answer 38

amplitude same for all particles

Question 39

What is the phase difference between two particles in a stationary wave like?

Answer 39

equal to mπ | m- number of nodes between two particles

Question 40

What is the phase difference between two particles in a progressive wave?

Answer 40

equal to 2πd/λ d= distance apart λ= wavelength

Question 41

What is sound in an air-filled tube or pipe like?

Answer 41

sound resonates at certain frequencies

Question 42

What happens to resonant frequencies in a pipe closed at one end?

Answer 42

resonant frequencies occur when there is an antinode at open end + node at other end

Question 43

Where are microwaves from a transmitter directed normally?

Answer 43

at a metal plate

Question 44

What does the metal plate do when a microwave from a transmitter is directed at it?

Answer 44

reflects microwaves back towards transmitter

Question 45

When a detector is moved along the line between a microwave transmitter and the metal plate, when is the detector signal found to be zero (or at a minimum?

Answer 45

at equally spaced positions along the line

Question 46

What do the reflected waves and waves from the transmitter form? (using microwaves)

Answer 46

stationary wave pattern

Question 47

What is the positions where no signal (or minimum) is detected? (using microwaves)

Answer 47

where nodes occur

Question 48

How are the nodes spaced? (using microwaves)

Answer 48

at intervals of half a wavelength