Chapter 5 Waves Flashcards
Define amplitude
A wave’s maximum displacement from the equilibrium position
Define frequency
The number of complete oscillations passing through a point per second
Define period
The time taken for one full oscillation
Define wave speed
The distance travelled by the wave per unit time
Define wavelength
The length of one whole oscillation - the distance between a point on the wave and the same point on the following one
What is the wave equation?
- v = fλ
- wave speed = frequency x wavelength
Describe a longitudinal wave and what they are made up of.
The oscillation of particles is parallel to the direction of energy transfer. They are made up of compressions (high pressure regions) and rarefactions (low pressure regions). They cant travel in a vacuum
Which direction are particles moving in a longitudinal wave?
Particles are always trying to move to the nearest compression and so move away from rarefactions
Describe a transverse wave.
- The oscillation of particles is perpendicular to the direction of energy transfer.
- All EM waves are transverse and travel at 3x10^8 ms-1 in a vacuum
What can displacement-distance graphs of waves tell you?
You can calculate the wavelength
What can you calculate from a displacement-time graph of a wave?
The time period
Define a wave’s phase.
- The phase of a point on a wave relative to the origin can be defined as the fraction of the wave cycle that has elapsed since the origin
- The position of a certain point on a wave cycle. Can be measured in degrees, radians or fraction of a cycle
Define phase difference.
How much a particle / wave lags behind another. Same units as phase
Define path difference
The difference in the distance travelled by two waves
Define superposition
Where the displacements of two waves are combined as they pass each other. The resultant displacement is the vector sum of each wave’s displacement
Define coherence
Coherent waves must have the same frequency and wavelength and a fixed phase difference
Define wavefront
A surface / line connecting points on a wave that have the same phase
What are the two types of interference?
- Constructive interference: occurs when the waves are in phase and so their displacements are added
- Destructive interference: occurs when the waves are completely out of phase and so their displacements are subtracted
When are two waves in phase?
Two waves are in phase if they are both at the same point of the wave cycle: the same frequency and wavelength.Their phase difference is a multiple of 360 degrees / 2pi
What is a progressive wave?
One that transfers energy from one point to another without any transfer of matter
What is a standing wave?
A wave that stores energy rather than trasnferring it from one place to another
What is path difference a measure of?
Path difference is a measure of how far ahead one wave is compared to another
What is a wave’s phase?
A wave’s phase at a given point is a measure of how far through its cycle the wave is. It is usually measured in radians, where a complete cycle is 2pi
What happens when two waves meet in phase?
They will undergo constructive interference