Chapter 16- Superposition Of Waves Flashcards
Constructive superposition def
When the waves add together to give maximum amplitude
Destructive superposition def
When waves combine to produce zero amplitude
Superposition can only occur for
Identical wave types
Interference effect def
A pattern of maxima and minima where the waves combine constructively or destructively at fixed positions relative to the sources
When there is a path difference of a wavelength then..
Constructive interference occurs
When the path difference is wavelength/2 then…
Destructive interference occurs
Positions of maximum amplitude occur when
The path difference is zero or a whole number of wavelengths
When waves are in phase
A constructive superposition takes place
Coherent def
Coherent sources have the same frequency and maintain a constant phase relationship (always in phase)
Stable interference patterns only occur if… (3)
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
Path difference eq
Path difference= n(order of maximum from the centre) x wavelength
Data stored on a CD is in what form?
Bytes- in ones and zeros
What does the CD look like?
Have lots of small bumps within the grooves and the surface of the CD has a clear plastic protective covering
How do CDs work?
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
Which method can you use to demonstrate CD
Standard microwave kit
Board with aluminium foil bits on a trolley
Microwave transmitter and receiver
Standing waves also called
Stationary waves
Standing waves created from
From superposition if two progressive waves with
• equal frequency
• equal amplitude
Moving in opposite direction
Points of zero amplitude within a standing wave
Node
Positions of maxima within a standing wave
Antinode
Separation distance between adjacent nodes or antinodes
Half a wavelength
Standing wave differ from travelling waves in the following ways (3)
- 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
When a pulse is sent along a rope that is fixed at one end what happens?
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
Which experiment to investigate standing waves in a string
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
Stringed instruments all produce
Standing waves
How is sound created in a stringed instrument
Energy transferred to surrounding air
This is then amplified
Produces a sound
How to amplify sound on an instrument w strings (2)
- resonating sound box
- electronically
Principle of stringed instruments seen with which method
Using a sonometer
Amplitude =
Volume
Frequency =
Pitch
For stringed instruments the frequency is greater for (3)
- shorter strings
- strings with greater tension
- strings that have a lower mass per unit length
String with only one antinode has frequency called
Fundamental frequency
Notes emitted by vibrations other than the fundamental are called…
Overtones
Overtones that have a whole number multiples of the fundamental frequency are…
Harmonics
What are wind instruments
Tubes in which standing air waves are formed from vibrations in a mouthpiece
But
Wave boundaries can be antinodes or nodes
In a wind instrument tube antinodes form at
The open ends as reflections always create antinodes
In a wind instrument nodes always form
At closed ends- where particles are unable to oscillate
Diffraction def
When a wave passes through a gap or is partially obstructed by a barrier, the wavefront spreads out
Method to demonstrate diffraction
Ripple tank
What do dark lines represent on water in ripple tank
Represent crests and troughs
When oscillator in ripple tank is adjusted to a higher freq what happens to
A) wavelength
B) spreading
A) shortens
B) spreading is reduced
When the width is similar to the wavelength the wavefronts are
Almost circular
Diffraction can be explained using…
Huygen’s construction
What does Huygen’s construction state
He considered every point on the wavefront as the source of a secondary spherical wave
The wavefront is the envelope of these secondary waves
What doesn’t diffract significantly into valleys and around the curvature of the Earth’s surface (2)
Short wave radio and television signals
What does a diffraction pattern show
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
Equation including:
• slit width (a)
• the angle between the central maximum and the first minimum
• wavelength
Sin [] = wavelength/ a
A surface with thousands of equally spaced parallel groves scored onto each centimetre
A diffraction pattern is produced
What is the object called?
A diffraction grating
What must the width of the spacing be of the same order of magnitude as
The wavelength of the light
The order of maximum def
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
Method of studying the diffraction of light
Using a laser through a diffraction grating
Can see the first 2/3 points of maxima in a diffraction pattern
Why do ultrasound images show much less detail than X-rays
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
Resolving power of the eye def
The smallest angular separation of the objects for which I1 and I2 can be distinguished separately
Charge of an electron
1.6x10 ^-19 C
