Chapter 16- Superposition Of Waves

Question 1

Constructive superposition def

Answer 1

When the waves add together to give maximum amplitude

Question 2

Destructive superposition def

Answer 2

When waves combine to produce zero amplitude

Question 3

Superposition can only occur for

Answer 3

Identical wave types

Question 4

Interference effect def

Answer 4

A pattern of maxima and minima where the waves combine constructively or destructively at fixed positions relative to the sources

Question 5

When there is a path difference of a wavelength then..

Answer 5

Constructive interference occurs

Question 6

When the path difference is wavelength/2 then…

Answer 6

Destructive interference occurs

Question 7

Positions of maximum amplitude occur when

Answer 7

The path difference is zero or a whole number of wavelengths
When waves are in phase
A constructive superposition takes place

Question 8

Coherent def

Answer 8

Coherent sources have the same frequency and maintain a constant phase relationship (always in phase)

Question 9

Stable interference patterns only occur if… (3)

Answer 9

Waves are the same type
Sources are coherent
Waves have similar amplitude at the point of superposition
Waves have similar amplitude at the point of superposition

Question 10

Path difference eq

Answer 10

Path difference= n(order of maximum from the centre) x wavelength

Question 11

Data stored on a CD is in what form?

Answer 11

Bytes- in ones and zeros

Question 12

What does the CD look like?

Answer 12

Have lots of small bumps within the grooves and the surface of the CD has a clear plastic protective covering

Question 13

How do CDs work?

Answer 13

Laser beam focused on groove is reflected back to the photodiode where light is converted into an electrical signal
Each bump has a height of 1/4 of wavelength of the laser, 1/4 of wavelength of radiation in the red/infrared region of electromagnetic spectrum.
Path difference between top of bump and bottom of groove means waves interfere destructively
Output of photodiode is zero
When entire beam is reflected from the upper surface or the gap then intensity of reflected beam is strong and high electrical output (1) generated by photodiode

Question 14

Which method can you use to demonstrate CD

Answer 14

Standard microwave kit
Board with aluminium foil bits on a trolley
Microwave transmitter and receiver

Question 15

Standing waves also called

Answer 15

Stationary waves

Question 16

Standing waves created from

Answer 16

From superposition if two progressive waves with
• equal frequency
• equal amplitude
Moving in opposite direction

Question 17

Points of zero amplitude within a standing wave

Answer 17

Node

Question 18

Positions of maxima within a standing wave

Answer 18

Antinode

Question 19

Separation distance between adjacent nodes or antinodes

Answer 19

Half a wavelength

Question 20

Standing wave differ from travelling waves in the following ways (3)

Answer 20

• standing ones store energy, travelling ones transfer
• amplitude of standing varies from zero to maximum, but amplitude along progressive wave is constant
• oscillations are all in phase between nodes, but phase varies continuously along a travelling wave

Question 21

When a pulse is sent along a rope that is fixed at one end what happens?

Answer 21

The reflected pulse is out of phase with the incident pulse
A phase change of 180* occurs at the point of reflection
This means that destructive interference occurs
The fixed position therefore will be a node

Question 22

Which experiment to investigate standing waves in a string

Answer 22

Melde’s experiment
String attached to oscillator passed over pulley wheel and kept taught by weight hanging at the end
Frequency is adjusted until antinodes and nodes are clearly visible
Strobe lamp used to help study the waves in more detail
Wavelength found by measuring between alternate nodes

Question 23

Stringed instruments all produce

Answer 23

Standing waves

Question 24

How is sound created in a stringed instrument

Answer 24

Energy transferred to surrounding air
This is then amplified
Produces a sound

Question 25

How to amplify sound on an instrument w strings (2)

Answer 25

- resonating sound box | - electronically

Question 26

Principle of stringed instruments seen with which method

Answer 26

Using a sonometer

Question 27

Amplitude =

Answer 27

Volume

Question 28

Frequency =

Answer 28

Pitch

Question 29

For stringed instruments the frequency is greater for (3)

Answer 29

* shorter strings * strings with greater tension * strings that have a lower mass per unit length

Question 30

String with only one antinode has frequency called

Answer 30

Fundamental frequency

Question 31

Notes emitted by vibrations other than the fundamental are called...

Answer 31

Overtones

Question 32

Overtones that have a whole number multiples of the fundamental frequency are...

Answer 32

Harmonics

Question 33

What are wind instruments

Answer 33

Tubes in which standing air waves are formed from vibrations in a mouthpiece But Wave boundaries can be antinodes or nodes

Question 34

In a wind instrument tube antinodes form at

Answer 34

The open ends as reflections always create antinodes

Question 35

In a wind instrument nodes always form

Answer 35

At closed ends- where particles are unable to oscillate

Question 36

Diffraction def

Answer 36

When a wave passes through a gap or is partially obstructed by a barrier, the wavefront spreads out

Question 37

Method to demonstrate diffraction

Answer 37

Ripple tank

Question 38

What do dark lines represent on water in ripple tank

Answer 38

Represent crests and troughs

Question 39

When oscillator in ripple tank is adjusted to a higher freq what happens to A) wavelength B) spreading

Answer 39

A) shortens | B) spreading is reduced

Question 40

When the width is similar to the wavelength the wavefronts are

Answer 40

Almost circular

Question 41

Diffraction can be explained using...

Answer 41

Huygen's construction

Question 42

What does Huygen's construction state

Answer 42

He considered every point on the wavefront as the source of a secondary spherical wave The wavefront is the envelope of these secondary waves

Question 43

What doesn't diffract significantly into valleys and around the curvature of the Earth's surface (2)

Answer 43

Short wave radio and television signals

Question 44

What does a diffraction pattern show

Answer 44

Shows a central maximum edged by a series of lower intensity maxima and minima as opposed to a regular pattern of interference from a double slit Central maxima will broaden when slit width is reduced

Question 45

Equation including: • slit width (a) • the angle between the central maximum and the first minimum • wavelength

Answer 45

Sin [] = wavelength/ a

Question 46

A surface with thousands of equally spaced parallel groves scored onto each centimetre A diffraction pattern is produced What is the object called?

Answer 46

A diffraction grating

Question 47

What must the width of the spacing be of the same order of magnitude as

Answer 47

The wavelength of the light

Question 48

The order of maximum def

Answer 48

The points of maxima graded from the one point of reflected light in line with the incident ray n=0 is the first and then it goes out by one each side

Question 49

Method of studying the diffraction of light

Answer 49

Using a laser through a diffraction grating | Can see the first 2/3 points of maxima in a diffraction pattern

Question 50

Why do ultrasound images show much less detail than X-rays

Answer 50

Because X-rays have a much shorter wavelength then the ultrasound Depends also on its diameter Image resolution is limited by the diffraction that occurs at the aperture of the receiver

Question 51

Resolving power of the eye def

Answer 51

The smallest angular separation of the objects for which I1 and I2 can be distinguished separately

Question 52

Charge of an electron

Answer 52

1.6x10 ^-19 C