waves Flashcards
what is a progressive wave?
- a wave that transfers energy from one point to another without transferring the medium itself
what is the displacement of a wave?
- distance of a point on the wave from its equilibrium position
what is the amplitude of a wave?
- maximum displacement of a particle in the wave from its equilibrium position
what is wavelength?
- distance between points on successive oscillations of the wave that are in phase
what is the period of a wave?
- time taken for one complete oscillation
what is the frequency of a wave?
- number of oscillations per unit time
what is phase difference?
- a measure of how much a point on a wave is infront or behind another
what happens when crests or troughs are aligned?
- waves are in phase
what happens when crest aligns with troughs?
- waves are in antiphase
what are transverse waves?
- waves which the particles oscillate perpendicular to direction of wave travel
what are longitudinal waves?
- waves which oscillate parallel to direction of wave travel
what are compressions?
- regions of increased pressure
what are rarefactions?
- regions of decreased pressure
give 3 examples of transverse waves
- electromagnetic waves
- waves on a string
- vibrations on a guitar string
give 3 examples of longitudinal waves
- sound waves
- ultrasound waves
- waves through a slinky coil
what is polarisation?
- when particle oscillations occur in only one of the directions perpendicular to the direction of wave travel
explain the effect of a polarising filter
- restricts oscillations of the wave into a certain direction depending on axis
- intensity of light will decrease
explain what happens if unpolarised light is placed infront of two identical polarising filters, with their transmission axis parallel
- filter A will polarise the light in a certain axis
- all of the polarised light will pass through filter B unaffected
- maximum intensity of light observed
explain what happens as filter B is rotated anticlockwise at an angle
- intensity of light changes depending on angle
- when A and B have their transmission axis perpendicular to each other, intensity is minimum
what graph and equation will intensity of light follow?
cos graph
I = Io cos^2theta
how are stationary waves produced?
- superposition of two waves with same frequency and amplitude travelling in opposite directions
how do stationary waves differ from progressive waves?
- they store energy, not transfer
- they have nodes and antinodes
- each point has a diff amplitude depending on amount of superposition
what are nodes and antinodes?
nodes are regions of no vibration
antinodes are regions of maximum vibrations
what is the principle of superposition?
- when two or more waves with the same frequency and amplitude arrive at a point, the resultant displacement is the sum of the displacement of each wave
what happens when two progressive waves arrive in phase?
- they cause constructive interference, peaks and troughs line up on both waves
- resultant wave has double the amplitude
what happens when two progressive waves arrive in antiphase?
- destructive interference occurs
- peaks on one wave line up with troughs on other wave, resultant wave has no amplitude
whats the rule for number of antinodes and nodes on a stationary wave for harmonics
nth harmonic has n antinodes and n+1 nodes
how do you calculate frequency of first harmonic
v = sqrt T / u
v = f lambda = f x 2l
2fl = sqrt T / u
f = 1/2l sqrt T / u
what is constructive interference
when two waves arrive in phase their combind effect makes resultant amplitude larger
what is destructive interference
when two waves arrive in antiphase, their combined effect means they cancel each other out
what is meant by coherent sources
- same frequency
- constant phase difference
what is meant by path difference
- difference in distance travelled by two waves from their sources to the point where they meet
