Waves Flashcards
Amplitude?
Maximum displacement from a central equilibrium position
Frequency?
The number of waves per second passing a point
Wave period?
The time for one wave to pass a point
Wave speed?
The velocity at which a wave front moves
Wavelength?
Distance between one wave crest and the next
Wavefront?
A line joining points on a wave which oscillate in phase with each other
Transverse waves?
Oscillate perpendicular to the direction of travel
Longitudinal wave?
Oscillations parallel to direction of travel so that a compression is followed by a rarefraction
Longitudinal wave in terms of pressure variation and displacement of molecules
Superposition
The net displacement of the medium at any point in space or time
Is simply the sum of the individual wave displacements
What conditions are needed to produce a steady interference pattern (COHERENT WAVES)?
Same frequency
Similar amplitude
Constant phase relationship
Coherence?
Waves with the same frequency and constant phase difference
Path difference?
For 2 waves starting from different points and arriving at the same point, the path difference is the difference in the length travelled by each wave (m).
In-Antiphase?
When the phase difference between two waves is 180º or π radians
In-Phase
When the phase difference between two waves is 0º or 0 radians
Phase difference?
The difference in phase (measures in º or radians)
It can be seen as the amount by which one wave lags behind the other
Standing wave?
A wave that stores energy instead of transferring it.
A common example is a string fixed at both ends.
They are formed by a wave propagating and being reflected so that it comes into superposition with itself.
Explain how a standing wave is set up on a string (6 marks)
- 2 waves travelling in opposite directions
- wave reflects and superposes itself
- constructive interference- ANTINODES
- destructive interference- NODES
- antinodes = max displacement
- nodes = min displacement
Things to mention for a 6 marker on polarisation
- light from source is unpolarised
- intensity of the light
- no light passes when the filter is rotated 90º as the plane is now perpendicular to the light
- a COMPONENT of the light intensity can pass through
- when the filter is rotated at 0º or 180º, the plane of polarisation is aligned and light passes at full intensity
- absorb perpendicular components, transmit parallel components
Define plane polarised
Transverse waves in which the direction of oscillations occur in a single plane and are perpendicular to the direction of propagation
Polarisation definition
The process by which the oscillations are made to occur in one plane only
This plane includes the direction of travel of the wave
What are 3 ways we can polarise light?
Polaroid filter
Reflecting light off a surface
Light scattering through the atmosphere
What happens to the intensity of light if a Polaroid is used on unpolarised light
The intensity will reduce by half
What happens to microwaves when you have vertical
Huygen’s principle
As waves pass through a gap, the SPREAD OUT
Each point on the wave front acts as a source of new waves
What is the principle of conservation of linear momentum
The momentum of a system is fixed unless an external force acts
