Sam Ellis Waves Flashcards
2 defining features of transverse waves
Direction of energy propogation is at 90º to the oscillations
Can travel through a vacuum
2 Defining features of longitudinal waves
Direction of energy propogation is parallel to the oscillations
need a medium to transfer energy
What is meant by amplitude?
Magnitude of maximum displacement.
What makes a wave a wave?
a disturbance in a medium that carries energy without a net movement of particles
How would you calculate phase difference?
2π(d/lambda) the whole cycle times the fraction of the whole wave
When are waves in phase?
0, 2π, 4π, 6π, 8π etc
When are waves completely out of phase?
odd multiples of π
What is the principle of superposition?
when two or more waves with the same frequency
travelling in opposite directions overlap,
the resultant displacement is the sum of displacements of each wave
What is polarisation?
Reducing transverse wave oscillations in a particular direction.
What is a real life application of polarisation?
Polaroid lenses in sunglasses for driving - the road will reflect waves in a plane, the glasses will have filters oriented such that the reflections do not show
On a stationary wave - what is an anti node?
A point with MAX amplitude
On a stationary wave - what is a node?
A point with no displacement.
What is total destructive interference, when does it occur?
When two waves completely out of phase interfere they completely cancel each other out leading to no resultant displacement.
When will a standing wave occur?
superposition of two waves of the same frequency and amplitude travelling in opposite directions.
Constructive inteference occours at anti nodes
total destructive at nodes
What must be true about stationary waves formed in a loudspeaker?
there must be a minima (node) at one end and a maxima (antinode) at the end with the loudspeaker.
With reference to motion, what is true about nodes and anti nodes
The nodes and antinodes do not move along the string. Nodes are fixed and antinodes only move in the vertical direction
What is Diffraction?
the spreading out of waves when they pass an obstruction.
What is meant by coherent?
The same frequency
A constant phase difference
What is path difference? What must be true about it for constructive / destructive interference to occur?
The difference in distance travelled by two waves from their sources to the point where they meet
The condition for constructive interference is a path difference of nλ
The condition for destructive interference is a path difference of (n + ½)λ
Give 3 precautions when using a laser.
Never look directly at a laser or its reflection
Don’t shine the laser towards a person
Don’t allow a laser beam to reflect from shiny surfaces into someone else’s eye
What do D w and s stand for in the fringe spacing seperation
w = fringe spacing
D = Distance from screen to slits
s = slit seperation
When is diffraction the most prominent?
Diffraction is the most prominent when the width of the slit is approximately equal to the wavelength
What is the only property of a wave that changes when it diffracts?
The only property of a wave that changes when it diffracts is its amplitude
What would happen if the blue laser were to be replaced with a red laser
The wavelength of red light is longer so the light would diffract more
The intensity fringes would therefore be wider
Narrower slit = ?
MORE DIFFRACTION
Less intense
more spread out
What is different about energy in stationary waves vs progressive waves
Stationary waves store energy, unlike progressive waves which transfer energy.
What does T and ‘Mu’ stand for in the first harmonic equation?
Mu is MASS per unit length
T is tension
Sketch a single slit diffraction pattern for blue laser light.
Bright central maxima
Other maxima half the width
With single slit diffraction how does the amount of diffraction change with the slit spacing?
More wide = less diffraction
If we have a longer wavelength say red compared to blue what happens to diffraction pattern through the same slit?
The wavelength of red light is longer so the light would diffract more
The intensity fringes would therefore be wider
If the wavelength is longer it diffracts…
MORE
What do all the symbols stand for in dSin(ø) = nY?
d = slit spacing
n = order
lambda = wavelength
ø = angular separation between orders
Conditions for TIR?
The angle of incidence > the critical angle
The refractive index n1 is greater than the refractive index n2
If the angle of incidence was 55º and TIR occured what is the other angle?
55º also
