Waves Flashcards
Define transverse wave.
Particle oscillation is perpendicular to the direction of energy transfer. They can travel through a vacuum.
Define longitudinal wave.
Particle oscillation is parallel to the direction of energy transfer. They can’t travel through a vacuum.
Define particle displacement.
The displacement from equilibrium position in the direction of the wave.
Define amplitude.
Maximum particle displacement.
Define wavelength.
The shortest distance between two points in phase.
What’s the difference between a polarised and unpolarised wave?
An unpolarised wave will have particle oscillations in every direction perpendicular to the energy transfer; a polarised wave will only have particle oscillations in one direction perpendicular to the direction of energy transfer.
Define stationary wave.
A wave that doesn’t transfer energy, formed when a progressive wave is reflected at a boundary and superposes the original wave.
What is required of the superposing progressive waves in order for a stationary wave to occur?
- Same wavelength
- Same frequency
- Similar amplitudes
- Must be travelling in opposite directions.
What happens at the nodes on a stationary wave?
Destructive interference occurs and particles have no amplitude or energy.
Phase difference between corresponding points on the incident and reflected wave is 180 degrees and path difference is a multiple of n/2 wavelengths.
What happens at the anti-nodes on a stationary wave?
Constructive interference occurs and particles have maximum energy and amplitude. Phase difference between corresponding points on incident and reflected waves is 0 degrees and path difference is a multiple of n wavelengths.
How far apart a nodes?
Nodes are half a wavelength apart. All particles between nodes are in phase, and particles either side of a node are 180 degrees out of phase.
Pipes with one open end will have…
A node at the closed end and an anti-node at the open end. Even harmonics are not possible, as that would require a node at the open end, which isn’t possible.
Pipes with two open ends will have…
Anti-nodes at either end and a node in the middle.
Define coherent source.
Sources with same wavelength and constant phase difference.
Define phase difference.
The difference in angle between two waves.
Define path difference.
The difference in distance traveled by two waves two the same point.
How are fringes formed from a diffraction grating different to those formed from double slits?
They are brighter and narrower.
How do polarised sunglasses work?
- Sunlight reflected off a boundary is weakly polarised in one plane, which causes glare.
- Polarised sunglasses are orientated so that this reflected light cannot pass through, therefore eliminating the glare.
What’s diffraction?
The spreading of waves after passing an obstacle or passing through an aperture of similar size to the wavelength.
A monochromatic, coherent laser shone through a single slit will…
Produce a central maxima twice the width of the other maxima.
Define refraction.
A change in wavelength, and therefore speed, when a wave goes from one material to another with different density.
A light ray entering a more dense material will…
Bend towards the normal.
