Waves (C11, C12) Flashcards
What are mechanical waves caused by?
An oscillating object
D transverse wave
move away from the source and oscillates perpendicular to propagation
What are longitudinal waves made up of
Compressions and rarefractions
What is an example of a non-mechanical wave
EM radiation
What do you have to be careful with wave graphs
The axis!
Displacement v time graph
oscillator
Displacement v position
Wave
D wavelength
distance between two adjacent in phase points
D period
time for one complete cycle or oscillation
D frequency
number of wave cycles per second
D Amplitude
Maximum displacement from the equilibirum position
D Phase difference
Relationship between the patterens of oscillators
D in phase
Pattern of oscillators are identical
D anti phase
pattern of oscillation is opposite at any point
What is a phasor
the circle that maps the curve that represents the wave
How is intensity related to amplitude?
I is proportional to amplitude squared
Four characteristics of wave behaviour
reflect
refract
diffract
interfere
Difference between ray and wave front
Ray is direction of propagaation and wave front is a line connecting in phase points
Angle of incidence = ?
Angle of reflection
What is specular reflection/
Parrallel refelct at same angle
D diffuse reflection
vaired normals means lots of angles
Two special cases of refraction
Dispersion and Total internal refraction
Why does refraction occur
change in medium
change in speed
change in wavelength
If angular if it speeds up bends away from normal and if it slows then it bends towards normal
What type of wave doesn’t get faster in a higher density or depth?
Light (EM wave)
What does a converging lens correct
long sightedness
What does a diverging lens correct?
short sightedness
What is n in waves?
refraction index c/v (therefore must be >=1)
In total internal relfection what is special about the angle of incidence when the angle of reflection is 90 degrees
it is called the critical angle
TIR occurs when
angle of incidence is greater than the critical angle
What law relations refractive index
snells law n1sin01 = n2sin02
Why does dispersion occur?
different frequencies refract different amounts due to their different speeds
What colour refracts the least
red
What causes diffraction
Wave passing through a gap
d»lambda
little diffraction
d=lambda
noticable diffraction (some straight parts)
d «_space;lambda
strong diffraction (big curves)
What is an EM wave made of?
Electric and magnetic fields
What are teh three types of UV and what are their characteristics?
UVA - tanning, destroys collagen
UVB - burns, cancer and vit D
UVC - broken down by ozone
What is polarisation?
When all oscillations of a field are limited to one plane only (electric field)
Name two ways of polarised waves coming about
Production
Filter
When does a grill block EM radiation
Parallel grill and wave
What law links amplitude and intensity
Malus’s law
What happens when two waves meet?
They SUPERPOSE
What is constructive interference?
The superposition of two waves in phase such that the resultant displacement is greater than either of the initial displacements
Destructive interference
Superposition of two waves in antiphase such that the resultant displacement is zero
What is the principle of superposition
Total displacement = vector sum of the displacements of each wave at that point
What makes two sources coherant?
Whether they produce a stable interference pattern, i.e have a constant phase difference
What is the central line between two sources called?
Central maximum
What is path difference?
difference in distance to point of intereference from each source
What are other maxima called?
Subsidary maxima (1st order than 2nd order etc)
path difference for desttrucutive interference?
(n=1/2)*lambda
path difference for constructive interference?
n*lambda
Where is n counted from in path difference/
central maxima
What are characteristics of coherant sources?
Same frequency and constant phase difference
What has to be true about the young’s double slit equation?
The slit separation has to be much much smaller than the distance between the source and the interference pattern
What type of light is used in the Young’s double slit experiment?
monochromatic (laser or bulb passed through a filter)
double slit - What happens when one slit is wider than the other?
No points of destructive intereference
What happens with double slit of white light? colour order?
Colours interefere and diffract different amounts
white in middle and then spectrums with violet coloses to centre and red furthest away
How is a stationary wave made?
Two indentical waves travelling in opposite directions
2 methods of making a stationary wave?
send tow waves at each other
1 wave source that reflects
What is a point of amplitude zero called on a stationary wave/
Node
What is an antinode?
Point on a stationary wave that vibrates with maximum energy and amplitude
Where is max KE on a stationary wave
When an antinode is flat
Where is in phase on a stationary wave?
Between nodes
Where is antiphase on a stationary wave?
either side of a node
What doesn’t matter for phase difference?
displacement
What is the first stationary wave known as?
fundamental mode of oscillation (f0)
What’s the best way to understand a stationary wave question?
sketch
What is an open end of a tude
antinode
What is a closed end
node
What type of wave is in a stationary wave tube
longitudinal wave
