Module 4 Waves

Question 1

What are progressive waves?

Answer 1

A progressive (moving) wave caries energy from one place to another without transferring any material. The transfer of energy is in the same direction as the wave is travelling.

Question 2

How can you tell waves are transferring energy (don’t learn but have rough idea)

Answer 2

1) Electromagnetic waves cause things to heat up.
2) X-rays and gamma rays knock electrons out of their orbits, causing ionisation.
3) Loud sounds cause large oscillations in air particles which can make things vibrate.
4) Wave power can be used to generate electricity.

Question 3

What happens to the energy levels of the source of the wave

Answer 3

Since waves carry energy away, the source of the wave loses energy.

Question 4

What is displacement on a wave
What’s it measured in
What’s its symbol

Answer 4

how far a point on the wave has moved from its undisturbed position.
Measured in meters
Symbol is x

Question 5

What is amplitude on a wave
What’s it measured in
What’s its symbol

Answer 5

the maximum magnitude of the displacement.
Measured in meters
Symbol is A

Question 6

What is wavelength on a wave
What’s it measured in
What’s its symbol

Answer 6

the length of one whole wave cycle, e.g. from crest to crest or trough to troug
Measured in meters
Symbol λ

Question 7

What is period on a wave
What’s it measured in
What’s its symbol

Answer 7

the time taken for a whole cycle (vibration) to complete.
Measured in seconds
Symbol is T

Question 8

What is frequency on a wave
What’s it measured in
What’s its symbol

Answer 8

the number of cycles (vibrations) per second passing a given point. (F= ossilations / time)
Measured in hertz
Symbol f

Question 9

What is phase on a wave
What’s it measured in
What’s its symbol

Answer 9

a measurement of the position of a certain point along the wave cycle.
Measured in degrees / radians
No symbol

Question 10

What is phase difference on a wave
What’s it measured in
What’s its symbol

Answer 10

the amount one wave lags behind another.
Measured in degrees /radians
No symbol

Question 11

Equation to calculate period

Answer 11

Frequency = 1/period

(Therefore 1 Hz = 1 s^-1

Question 12

Two equations used to calculate wave speed

Answer 12

Wave speed (v) = distance (d) /time (t)

Wave speed (v) = frequency (f) x wavelength (λ)

Question 13

What does a cathode ray oscilloscope do?

Answer 13

A cathode ray oscilloscope (CRO) measures voltage.
It displays waves from a signal generator as a function of voltage over time.

Question 14

What is the wave displaced on a CRO called

Answer 14

A trace

Question 15

What are the squares on a CRO called

Answer 15

Divisions

Question 16

What are the axis measured in on a CRO and which dial does what?

Answer 16

The vertical axis is in volts. The volts per division shown on this axis is controlled by the gain dial.

The horizontal axis is in seconds - also called the timebase. The seconds per division shown on this axis is controlled by the timebase dial.

You can alter the gain and timebase to make it easy to read off measurements.

Question 17

What traces on an oscilloscope do you get if you plug:
An AC
A microphone

Answer 17

1) If you plug an AC (alternating) supply into an oscilloscope, you get a trace that goes up and down in a regular pattern - some of the time it’s positive and some of the time it’s negative.
2) A microphone converts sound waves into electrical signals which can be seen on an oscilloscope.

Question 18

How do you calculate frequency using an oscilloscope

Answer 18

Look at CGP

Question 19

What are some examples of transverse waves

Answer 19

EM waves
Ripples on water

Question 20

How are transverse waves shown on displacement distance and displacement time graphs

Answer 20

Looks like a sin graph on both

:
(Make sure displacement axis has a positive and negative sign above and below the equilibrium position)

Question 21

Gives some examples of longitudinal waves

Answer 21

Sound
Earthquake shock waves (p waves)

Question 22

How are longitudinal waves represented graphically

Answer 22

It’s hard to represent longitudinal waves graphically. You’ll usually see them plotted as displacement against time. These can be confusing though, because they look like a transverse wave.

Question 23

How do longitudinal waves travel through a medium

Answer 23

A longitudinal wave (such as a sound waves) consists of alternate compressions and rarefactions of the medium it’s travelling through. (That’s why sound can’t go through a vacuum.)

Question 24

What is the difference between how longitudinal and transverse waves oscillate

Answer 24

The direction of oscillation of a wave is perpendicular to the direction of motion of the wave.

The direction of oscillation of a wave is parallel to the direction of motion of the wave.

Question 25

What is intensity?

Answer 25

Intensity is the rate of flow of energy per unit area at right angles to the direction of travel of the wave. It’s measured in Wm-2

(Informality: Intensity is a Measure of How Much Energy a Wave is Carrying)

Question 26

Equation for intensity

Answer 26

Intensity =Power/Area

Question 27

How are intensity and amplitude related, from this relationship what can you tell about how much energy it takes to double the size of the vibrations

Answer 27

Intensity = (Amplitude)^2

This comes from the fact that intensity is proportional to energy (due to it effecting the speed wave travels) , and the energy of a wave depends on the square of the amplitude.

From this you can tell that for a vibrating source it takes four times as much energy to double the size of the vibrations.

Question 28

Name some properties of em waves including
speed in a vacuum
The type of wave including what makes up the wave
Can they be refracted reflected and diffracted and under go interference
Are they progressive waves
Can they be polarized

Answer 28

1) All EM waves travel in a vacuum at a speed of 3.00 x 108 ms- (to 3 s.f.), and at slower speeds in other media.
2) They are transverse waves consisting of vibrating electric and magnetic fields.
The electric and magnetic fields are at right angles to each other and to the direction of travel.
3) Like all waves, EM waves can be refracted (p.84), reflected and diffracted (p.82-83) and can undergo interference (p.86).
4) Like all progressive waves, progressive EM waves carry energy.
5) EM waves are transverse so, like all transverse waves, they can be polarised (see page 80).

Question 29

Name the EM spectrum in order of magnitude

Answer 29

radio waves
microwaves
infrared
visible light
ultraviolet
X-rays
gamma rays

Question 30

Which waves have the highest and lowest energy and why can this be explained

Answer 30

Energy is directly proportional to frequency. Gamma rays have the highest energy; radio waves the lowest

Question 31

What do longer wave lengths mean

Answer 31

The longer the wavelength, the more obvious the wave characteristics - long radio waves diffract round hills.

Question 32

How does danger very on the EM spectrum

Answer 32

In general, the higher the energy, the more dangerous the wave

Question 33

What is the penetration, aprox wavelength and uses of radio waves?

Answer 33

Aprox wavelength: 10^-1 10^6
Penetration: pass through matter
Uses: radio transmission

Question 34

What is the penetration, aprox wavelength and uses of micro waves?

Answer 34

Aprox wavelength: 10^-3 10^-1
Penetration: mostly pass through matter but cause some heating
Uses: Radar. Microwave cooking.TV transmissions.

Question 35

What is the penetration, aprox wavelength and uses of infrared radiation?

Answer 35

Aprox wavelength: 7 x 10^-7. 10^-3
Penetration: Mostly absorbed by matter, causing it to heat up.
Uses: Heat detectors. Night vision cameras. Optical fibers.

Question 36

What is the penetration, aprox wavelength and uses of visible light?

Answer 36

Aprox wavelength: 4 x 10^-7 <— 7x 10^-7
Penetration: Absorbed by matter, causing some heating.
Uses: Human sight. Optical fibres.

Question 37

What is the penetration, aprox wavelength and uses of ultraviolet light?

Answer 37

Aprox wavelength: 10^-8. 4×10^-7
Penetration: Absorbed by matter. Slight ionisation.
Uses: Sunbeds. Security marks that show up under UV.

Question 38

What is the penetration, aprox wavelength and uses of X-rays ?

Answer 38

Aprox wavelength: 10^-13 10^-8
Penetration: Mostly pass through matter, but cause ionisation as they pass.
Uses: To see damage to bones and teeth. Airport security scanners. To kill cancer cells.

Question 39

What is the penetration, aprox wavelength and uses of gamma rays?

Answer 39

Aprox wavelength: 10^-16 10^-10
Penetration: Mostly pass through matter, but cause ionisation as they pass.
Uses: Irradiation of food. Sterilisation of medical instruments. To kill cancer cells.

Question 40

What is plane polarization?

Answer 40

Polarising a wave so that it only oscillates in one direction

(Look at rope example on cgp)

Question 41

What are ordinary light waves made up of

Answer 41

Ordinary light waves are a mixture of different directions of vibration.
(The things vibrating are electric and magnetic fields).

Question 42

What does a polarizing filter do

Answer 42

A polarising filter only transmits vibrations in one direction.

Question 43

What happens if two polarizing filters are a right angles

Answer 43

then no light will get through.

Question 44

What types of waves can polarization occur for

Answer 44

Transverse waves

Question 45

Understanding how to complete pag 5

Answer 45

.

Question 46

What is diffraction

Answer 46

The way that waves spread out as they come through a narrow gap or go round obstacles is called diffraction.

Question 47

What does the amount of diffraction depend on

Answer 47

The amount of diffraction depends on the size of the gap in comparison to the wavelength of the wave.

Question 48

What is a ripple tank

Answer 48

Ripple tanks are shallow tanks of water that you can generate a wave in.

Question 49

How do you generate waves in a ripple tank

Answer 49

This is done by an oscillating paddle, which continually dips into the water and creates regular waves with straight, parallel wave fronts.

Question 50

How can a ripple tank be used to show diffraction

Answer 50

Objects are then placed into the ripple tank to create a barrier with a gap in the middle of it.
This gap can be varied to see the effects this has on how the waves spread through the tank.

When the gap is a lot bigger than the wavelength, diffraction is unnoticeable.

You get noticeable diffraction through a gap several wavelengths wide.

You get the most diffraction when the gap is the same size as the wavelength.

Question 51

What happens to diffraction as the gaps a wave pass through become smaller

Answer 51

As the gap decreases, the diffraction becomes more noticeable until the gap becomes too small and the water waves cannot pass through it anymore. The waves are then reflected back on themselves.

Question 52

Use your understanding of wavelength and diffraction to explain why you can hear someone through a doorway but cannot see light through it

Answer 52

When sound passes through a doorway, the size of gap and the wavelength are usually roughly equal, so a lot of diffraction occurs. That’s why you have no trouble hearing someone through an open door to the next room, even if the other person is out of your line of sight. The reason that you can’t see him or her is that when light passes through the doorway, it is passing through a gap around a hundred million times bigger than its wavelength
- the amount of diffraction is tiny.

Question 53

What happens when a wave meets an obstacle?

Answer 53

When a wave meets an obstacle, you get diffraction around the edges. Behind the obstacle is a ‘shadow’, where the wave is blocked. The wider the obstacle compared with the wavelength of the wave, the less diffraction you get, and so the longer the shadow.

Question 54

How can you demonstrate diffraction in light using laser light or a white light source ?

Answer 54

Diffraction in light can be demonstrated by shining a laser light through a very narrow slit onto a screen (see the next page). You can alter the amount of diffraction by changing the width of the slit.

You can do a similar experiment using a white light source instead of the laser (which is monochromatic) and a set of colour filters. The size of the slit can be kept constant while the wavelength is varied by putting different colour filters over the slit.

Question 55

What happens if the wave length of a light wave is similar to the size of the two aperture’s during young’s double slit (using a coherent light source) ?

Answer 55

If the wavelength of a light wave is roughly similar to the size of the aperture, you get a diffraction pattern of light and dark fringes.

The pattern has a bright central fringe with alternating dark and bright fringes on either side of it.

The narrower the slit, the wider the diffraction pattern.

Question 56

What is reflection
What can be said about angle of incidence and reflection?

Answer 56

Reflection means the wave is bounced back when it hits a boundary.
The angle of incidence always equals the angle of reflection.

Question 57

How can you use a ripple tank to show reflection

Answer 57

Set up the ripple tank so the oscillating paddle is creating regular waves with straight, parallel wave fronts.
Place a barrier in the tank at an angle to the wave fronts.

The angle the incoming waves make with the normal to the barrier is called the angle of incidence, i.

You should see the waves reflecting off the barrier and travelling in a different direction to the way they arrived.

The angle between the direction of the reflected waves and the normal to the barrier is called the angle of reflection, r.

You can change the angle of incidence to see that the angle of reflection changes by the same amount. They are always equal to each other.

(Diagram on CGP page 83)

Question 58

What is refraction

Answer 58

Refraction is the way a wave changes direction as it enters a different medium. The change in direction is a result of the wave slowing down or speeding up. You can tell if the wave is speeding up or slowing down by the way it bends towards or away from the normal.

Question 59

Is the wave speeding up or slowing down when it bend towards
How do the wave length and frequency change

Answer 59

If the ray bends towards the normal - it is slowing down. The ray is going from a less optically dense material to a more optically dense material.

If the ray bends away from the normal _ the wave is speeding up. It is going from an optically denser material to a less optically dense material.

The speed changes because the wavelength of the wave is
changing and the frequency stays constant (v = f^).

Question 60

How can you use a ray box and glass block to investigate refraction

Answer 60

Place a glass block on a piece of paper and draw around it.
Outline of block
Use the ray box to shine a beam of light into the glass block. Turn off any other lights so you can see the path of the light beam through the block clearly.
Trace the path of the incoming and outgoing beams of light either side of the block.
Remove the block and join up the two paths you’ve drawn with a Normal
straight line that follows the path the light beam took through the glass block. You should be able to see from your drawing how the path of the ray bent when entering and leaving the block.
Measure the angles of incidence (0) and refraction (0) where the light enters and exits the block. Air is less optically dense than glass, so as the light enters the glass block it bends towards the normal (0i> 0r) as it slows down. The beam should bend away from the normal as it exits the block (0i > 0r) and speeds up.

Question 61

What is absolute refractive index (include an equation)

Answer 61

The absolute refractive index of a material, n, is the ratio between the speed of light in a vacuum, c, and the speed of light in that material, v.

n=c/v

c = 3.00 x 108 ms

Question 62

What happens to light entering more optically dense materials

Answer 62

Light goes fastest in a vacuum. It slows down in other materials, because it interacts with the particles in them.
The more optically dense a material is, the more light slows down when it enters it.

Question 63

what can the refractive index of air be taken as)

Answer 63

The speed of light in air is only a tiny bit smaller than c. So you can assume the refractive index of air is 1.

Question 64

What is snells law

Answer 64

n (1) sin 0 (1)= n (2) sin 0 (2)

where n (1) is the refractive index of the first material, 0 (1) is the angle of incidence, n (2) is the refractive index of the second material and 0 (2) is the angle of refraction.

Question 65

How can snells law be explained

Answer 65

When a light ray passes across a boundary between two materials:
(Where n is the refractive index of the material light travels in and O is the angle the light ray makes with the normal of the boundary)

n sin A = constant

This means that for a light ray at a boundary between two materials, n sin O must be the same on either side.

Question 66

What does a Refractometer do?

Answer 66

You can use a device called a refractometer to accurately measure the refractive index of a material. The machine shines a beam of light at the sample. You then view the refracted beam through a microscope and measure its angle of refraction.

Question 67

Explain how you find a critical angle of incidence using a glass block

Answer 67

Shine a ray of light at a glass to air boundary, then gradually increase the angle of incidence. As you increase the angle of incidence, the angle of refraction gets closer and closer to 90°. Eventually the angle of incidence, 0i, reaches a critical angle C for which the angle of refraction 0r= 90°. The light is refracted along the boundary.

Question 68

What happens to refraction at angles of incidence greater C (critical angle) ? What’s this effect called

Answer 68

At angles of incidence greater than C, refraction is impossible. That means all the light is reflected back into the material. This effect is called total internal reflection.

Question 69

What can we say about snells law at the critical angle (For light hitting a material-to-air boundary (assuming the material is more optically dense))

Answer 69

SinC=1/n

Question 70

How can you use a glass block to investigate critical angles and total internal reflection

Answer 70

Shine a light ray into the curved face of a semi-circular glass block so that it always enters at right angles to the edge - this means the ray won’t refract as it enters the block, just when it leaves from the straight edge.

Vary the angle of incidence, i0, until the light beam refracts so much that it exits the block along the straight edge. This angle of incidence is the critical angle, C, for glass-air boundary.

If you increase the angle of incidence so it’s greater than C, you’ll find the ray is reflected from the straight edge of the block. (No refraction)

Look at diagram on cgp page 85

Question 71

What is another equation for intensity

Answer 71

I= P / 4 π r^2

(Because the total radiant power is spread evenly over an area (surface area of a sphere) )

Question 72

What happens to intensity when distance of a wave (r) doubles

Answer 72

Intensity is inversely proportional to 1/r^2

Question 73

What is the principle of superposition (for waves). When dealing with complex waves how can superposition be used?

Answer 73

When two or more waves cross the resultant displacement equals the vector sum of the individual displacements

“Superposition” means “one thing on top of another thing
“. You can use the same idea in reverse
-a complex wave can be separated out mathematically several simple sine waves of various sizes

Question 74

What is interference

Answer 74

When two or more waves superpose with each other, the effect is called interference.

Question 75

What are constructive and destructive interference

Answer 75

A crest plus a crest gives a bigger crest. A trough plus a trough gives a bigger trough
These are both examoles of constructive interference
A crest plus a trough of equal size gives… nothing. The two displacements cancel each other out completelv. This is called destructive interference

If the crest and the trough aren’t the same size, then the destructive interference isn’t total. For the interference to be noticeable, the two amplitudes should be nearly equal.

Question 76

How can you superimpose waves graphically

Answer 76

Graphically, you can superimpose waves by adding the individual displacements at each point along the x-axis and then plotting them

Question 77

What does two points on a wave being in-phase mean?

Answer 77

Two points on a wave are in phase if they are both at the same point in the wave cvcle. Points in phase have the same displacement and velocity.

If Q asks about two coherent sources interfering talk about phase difference

Question 78

When are two point in or exactly out of phase in terms of π

Answer 78

Two points with a phase difference of zero or a multinle of n x 360° are in nhase
Points with a phase difference of odd-number multiples of (2n+1) x 180° are exactlv out of phase.

Question 79

Can two waves be in phase?

Answer 79

You can also talk about two different waves being in phase. In practice this happens because both waves came from the same oscillator. In other situations there will nearly alwavs be a phase difference between two waves.

Question 80

What is coherence and why is need to observe interference

Answer 80

Two sources are coherent if they have the same wavelength and frequency and a fixed phase difference between them (tends to be 0 at AS level)

Interference still happens when you’re observing waves of different wavelength and frequency - but it happens in a jumble. In order to get clear interference
natterns the two or more sources must he coherent

Question 81

What does whether interference between a wave being constructive or destructive depend on?

Answer 81

Whether you get constructive or destructive interference at a point depends on how much further one wave has travelled than the other wave to get to that point (assuming the sources are coherent and in phase).

Question 82

What is path difference?

Answer 82

The amount by which the path travelled by one wave is longer than the path travelled by the other wave is called the path difference.

Question 83

Explain how you can determine if inference at a point will be constructive or destructive in terms of path difference

Answer 83

At any point an equal distance from both sources you will get constructive interference.
You also get constructive interference at any point where the path difference is a whole number of wavelengths.

This can be thought of Constructive interference occurs when:
path differences = n λ
(where n is an integer)

At points where the path difference is an odd number of half wavelengths, the waves arrive out of phase and you get destructive interference

Destructive interference occurs when:
path difference = (2n + 1) λ / 2= (n + ½) λ

Question 84

How can you use sound waves to observe interference

Answer 84

Connect two speakers to the same oscillator (so they’re coherent) and place them in line with each other.
2) Walk slowly across the room in front of them
You will hear varying volumes of sound. At the points where the sound is loudest, the path difference is a whole wavelength.
4) The sound will be quietest at points where the path difference is an odd number of half wavelengths.

See CGP for diagram and Kerboodle 224 (note in the kerboodle in mentions vertical phase differences at different points explaining why path difference have the effect they do)

Question 85

Why is it easy to demonstrate two source interference for sound or water waves

Answer 85

It’s easy to demonstrate two-source interference for either sound or water waves because they’ve got wavelengths of a handy size that you can measure.
2) You need coherent sources, which means the wavelength and frequency have to be the same.
The trick is to use the same oscillator to drive both sources. For water, one vibrator drives two dippers. For sound, one oscillator is connected to two loudspeakers.

Question 86

Explain young’s double slit experiment

Answer 86

See cgp page 88

Question 87

What is an experiment you can do with micro waves to see interference patterns

Answer 87

To see interference patterns with microwaves, vou can replace the laser and slits with two microwave transmitter cones attached to the same signal generator.
You also need to replace the screen with a microwave receiver probe (like the one used in the stationary waves experiment on page 93).
3) If you move the probe along the path of the green arrow, you’ll get an alternating pattern of strong and weak signals
- just like the light and dark fringes on the screen.

Question 88

What is young’s double slit formula and what requirement does it have to work

Answer 88

x= λ D/a

Where
The fringe spacing (x),
wavelength (λ)
spacing between slits (a)
the distance from slits to screen (D)

For all waves a<D

(a has to be much smaller than D so you can use trigonometry to find this equation - including a small angle approximation
of sin 0 = 0.)

Question 89

Why was young’s experiment important in the physics world?

Answer 89

Towards the end of the 17th century, two important theories of light were published - one by Isaac Newton and the other by a chap called Huygens. Newton’s theory suggested that light was made up of tiny particles, which he called “corpuscles”. And Huygens put forward a theory using waves.
2) The corpuscular theory could explain reflection and refraction, but diffraction and interference are both uniquely wave properties. If it could be shown that light showed interference patterns, that would help settle the argument once and for all.
3) Young’s double-slit experiment (over 100 years later) provided the necessary evidence. It showed that light could both diffract (through the narrow slits) and interfere (to form the interference pattern on the screen).

Question 90

Why use a diffraction grating ?

Answer 90

.
You get basically the same shaped pattern as for two slits - but the bright bands are brighter and
narrower and ne cark areas be ween are darker.
2) When monochromatic light (one wavelength) is passed through a grating with hundreds of slits per millimetre, the interference pattern is really sharp because there are so many beams reinforcing the pattern.
31 Sharper fringes make for more precise measurements as they are easier to tell apart and so are easier to measure

Question 91

What are maxima and minima in s interference pattern

Answer 91

Interference patterns contain a series of maxima and minima. At a maximum the waves interfere constructively, at a minimum they interfere destructively.

Question 92

What do the maxima of monochromatic light look like

Answer 92

Sharp lines

Question 93

What are zero and first order lines produced by a diffraction grating

Answer 93

There’s a line of maximum brightness at the centre called the zero order line.
The lines just either side of the central one are called first order lines.
The next pair out are called second order lines and so on.

See cgp page 90

Question 94

How can you calculate the angle between the first and zero order fringe

Answer 94

Using the fringe width, x, and the distance to the screen, D, the angle the 1st order fringe makes with the zero order line can be calculated using small angle approximations.

tan theta = theta and tan theta = x/D

So theta = x/D

Question 95

How can you knowing the slit separation for the diffraction grating ,d, and knowing the angle between the first and zero order , theta, and knowing the grating has N slits per metre. Calculate the wavelength of the incident light…

Answer 95

The slit separation, d, for the diffraction grating is given.
Find how many slots per metre (let this be N), then the slit separation, d, is just 1/N metres (the distance between one slit).

If you know the slit separation, d, what order maximum you’re observing, n, and the angle between this maximum and the incident light, u you can find the wavelength of the incident light

d sin theta = n λ

Question 96

What conclusion can you draw from the equation d sin theta = n λ

Answer 96

1) If λ is bigger, sin (theta) is bigger, and so theta is bigger. This means that the larger the wavelength, the more the pattern will spread out.
2) If d is bigger, sin (theta) is smaller. This means that the coarser the grating, the less the pattern will spread out.
3) Values of sin (theta) greater than 1 are impossible. So if for a certain n you get a result of more than 1 for sin (theta) you know that that order doesn’t exist.

Question 97

What happens when white light is put through a diffraction grating ?

Answer 97

1) White light is really a mixture of colours. If you diffract white light through a grating then the patterns due to different wavelengths within the white light are spread out by different amounts.
2) Each order in the pattern becomes a spectrum, with red on the outside and violet on the inside
The zero order maximum stays white because all the wavelengths just pass straight through.

Question 98

Why are diffraction grating used instead of prisms to produce spectra

Answer 98

Astronomers and chemists often need to study spectra to help identify elements
They use diffraction gratings rather than prisms because they’re more accurate.

Question 99

What is a stationary wave

Answer 99

A stationary wave is the superposition of two progressive waves with the same wavelength and frequency , moving in opposite directions.

Question 100

What another name a for a stationary wave?

Answer 100

Standing wave

Question 101

Difference between stationary and progressive waves

Answer 101

Stationary waves don’t transmit energy

Question 102

Explain how you could create a stationary wave (don’t learn but understand )

Answer 102

You can demonstrate stationary waves by attaching a vibration transducer at one end of a stretched string with the other end fixed. The transducer is given a wave frequency by a signal generator and creates that wave by vibrating the string.
The wave generated by the vibration transducer is reflected back and forth.
4) For most frequencies the resultant pattern is a jumble. However, if you alter the signal
generator so the transducer produces an exact number of waves in the time it takes for a wave to get to the end and back again, then the original and reflected waves reinforce each other.
5) At these “resonant frequencies” you get a stationary wave where the pattern doesn’t move - it just sits there, bobbing up and down. Happy, at peace with the world…

Question 103

Cgp page 92 look at each wave and explain what it’s frequency is in-terms of the fundamental mode of vibration

Answer 103

.

Question 104

What is a node on a stationary wave

Answer 104

Nodes are where the amplitude of the vibration is zero.

Question 105

What are antinodes on a stationary wave

Answer 105

Antinodes are points of maximum amplitude.

Question 106

How are the particles In a stationary wave vibrating

Answer 106

Each particle vibrates at right angles to the string.

Question 107

What happens to a stationary wave at resonant frequencies

Answer 107

At resonant frequencies, an exact number of half wavelengths fits onto the string.

Question 108

How can longitudinal stationary waves form in a wind instrument or other air columns

Answer 108

If a source of sound is placed at the open end of a flute, piccolo, oboe or other column of air, there will be some frequencies for which resonance occurs and a stationary wave is set up.

If the instrument has a closed end, a node will form there. You get the lowest resonant frequency when the length, I, of the pipe is a quarter wavelength.

Antinodes form at the onen ends of pines If both ends are open, you get the lowest resonant frequency when the length,l, of the pipe is a half a wave length

Question 109

How can you use a microwave to demonstrate stationary waves

Answer 109

1) Microwaves are produced by a microwave transmitter.
2) They are reflected off a metal reflecting plate back towards the transmitter.
3) The reflected and incoming waves interfere and set up stationary waves.
4) you can find the nodes and antinodes by moving the microwave receiver between the transmitter and the reflecting plate.
5) Whenever a node is detected. the meter will show a minimum value.
The meter will show a maximum reading when an antinode is detected.

Question 110

How can you use stationary waves to measure the speed of sound

Answer 110

1) You can create a closed-end pipe by placing a hollow tube into a measuring cylinder of water.
2) Choose a tuning fork and note down the frequency of sound it produces (it’ll be stamped on the side of it).
3) Gently tap the tuning fork and hold it just above the hollow tube. The sound waves produced by the fork travel down the tube and get reflected (and form a node) at the air/water surface.
4) Move the tube up and down until you find the shortest distance between the top of the tube and the water level that the sound from the fork resonates at (when the sound is at its loudesti.
5) Just like with any closed pipe, this distance is a quarter of the wavelength of the stationary sound wave.
6) Once vou know the frequency and wavelength of the stationary sound wave, you can work out the speed of sound (in air),
v, using the equation v = f λ

Question 111

How many wavelengths between 2 adjacent nodes (on a stationary wave)

Answer 111

Half a wave length of the original progressive wave

Question 112

How does phase difference work with stationary waves

Answer 112

All parts of a wave between a pair of nodes are in phase and on opposite sides of a node they are anti phase (phase difference of pi)

Question 113

What is the fundamental frequency

Answer 113

Minimum frequency of a stationary wave for a string

Question 114

Can you have a 2nd harmonic for a tube closed at 1 end

Answer 114

No, because the the frequency of the harmonic of a tube closed at one end is always a odd multiple of the fundamental frequency (therefore the wavelength of stationary wave in a opened at one end pipe can only be an odd number multiple of 1/4)

Question 115

What are interference and diffraction patterns and what must this show about light

Answer 115

alternating bands of dark and light.

These can only be explained using waves interfering constructively (when two waves overlap in phase) or intertering destructively (when the two waves are out ot phase).

Question 116

When find fringe separation where should you measure from in terms of the diffraction separation pattern?

Answer 116

Measure from the Centre of one dark fringe to another

Question 117

How to calculate number of spaces for a diffraction grating pattern

Answer 117

Number of fringes - 1

Question 118

What is a resonant frequency otherwise known as?

Answer 118

Fundamental frequency (f subscript 0) where each times this is multiplied by an integer the a new harmonic is created.