Waves Flashcards
For a moving observer: When do you add or subtract Uo
Towards: Add
Away: Subtract
For a moving source: when do you add and subtract Us
Towards: Subtract
Away: Add
What is a travelling wave?
A wave that transfers energy but not matter
What is a transverse and longitudinal wave
Transverse: Particles oscillate perpendicular to direction of energy transfer
Longitudinal: particles oscillate parallel to direction of energy transfer
What is time period and frequency
Time Period: Time taken for 1 complete oscillation
Frequency: Number of oscillations that pass a point in 1s
For a Displacement-Distance Graph:
Which direction shows a positive and negative displacement
What can you find with the graph
- Positive = Right
Negative = Left - Wavelength and amplitude
For a Displacement-Time Graph:
What does the graph represent
What can you find using the graph
- Movement of 1 particle
- Amplitude, Time Period, Frequency
Phase Difference:
What is the definition
What multiples of pi means is in phase and completely out of phase
- Fraction of a wavelength that one lags
the other - In phase: 2π, 4π…
Completely out of phase: 1π, 3π…
What are rays and wavefronts
Wavefront: Shows parts of waves that are
in phase with each other
Rays: Are perpendicular to the wavefronts
and show direction of energy
transfer
What is refraction
Change of wavelength, speed and direction of a wave as it passes into a new medium
What is the equation for index of refraction
n1 = c / v1
c = speed of light in vacuum
v1 = speed of light in medium
What are the 6 things that happens when a wave meets a boundary
Transmission
Reflection
Refraction
Diffraction
Absorption
Scattering
What happens to speed, wavelength, change in angle and frequency as a wave enters a dense medium
Speed: Decreases
Wavelength: Decreases
Change in Angle: 0̷1 > 0̷2
Frequency: Same
What is the angle of refraction at the critical angle
90°
What is superposition
When 2 or more waves cross, the resultant displacement equals the vector sum of individual displacements
What is interference
The result of superposition of 2 or more waves
What is constructive/destructive interference
When 2 waves meet to make a larger/smaller displacement
What happens if interference occurs between:
2 Crests
2 Troughs
Crest and Trough
2 Crests: Constructive, in phase
2 Trough: Constructive, in phase
Crests and Trough: Destructive,
Completely out of
phase
What does it mean for 2 wave to be coherent
If they have a constant phase difference between them
Requires both to have the same speed, frequency and wavelength
How is a standing wave formed
When 2 coherent waves with the same amplitude, travelling in opposite directions, interfere with each other, superposition occurs
What are nodes and antinodes
Nodes: points of zero displacement
Antinodes: points that oscillate with
maximum displacement
What points on a standing wave are:
In phase
Completely out of phase
In phase: Area between 2 nodes
Completely out of phase: Sides next to a
node
Let n be the harmonic number and c be wave speed
What is the equation for Length and Frequency for:
2 Closed Ends
2 Open Ends
1 Open and 1 Closed End
2C: L = 0.5nλ
F = nc/2L
2O: L = 0.5nλ
F = nc/2L
1O1C: L = 0.25nλ
F = nc/4L
What does a closed and open end form
Closed: Node
Open: Antinode
What is the Doppler effect
The apparent change in frequency of a wave due to relative motion between source and observer
How does measured wavelength, apparent wave speed and apparent frequency change with a:
Moving Source
Moving Observer
MS: Changes, Same, Changes
MO: Same, Changes, Changes
What are the conditions for constructive/destructive interference
Constructive:
Must be in phase (2nπ)
Path difference must be nλ
Destructive:
Must be out of phase [(2n+1)π]
Path difference must be (n+0.5)λ
Both:
Both waves must have the same frequency and wavelength
Waves must be coherent
