waves Flashcards
waves
phenomena which transfer energy without transferring any material
cycle
one complete vibration
displacement
how far a point on the wave has moved from its undisturbed position (equilibrium)
amplitude
maximum displacement
wavelength
the length of one whole wave cycle
period
time taken for a whole cycle 1/f
frequency
oscillations/cycles per second
phase
measure of how far through a cycle a wave is
phase difference
the amount one wave lags behind another
diffraction
light spreads out as it passes around an object or through a narrow gap
refraction
bending of light as it enters a new medium with a different optical density
light changing speed
c
speed of light in a vacuum
3.0 E8 ms-1
transverse waves
oscillation perpendicular to direction of energy propagation
EM, water, string, Seismic-S
can be polarised
longitudinal waves
oscillations parallel to direction of propagation
compression (increased pressure) and rarefraction
cannot be polarised
sound, slinky, Seismic-P
polarisation
restriction of oscillations of waves to one plane only
process of filtering transverse waves
polarised waves oscillate in one direction
evidence EM waves are transverse
mechanical waves
oscillations vibrate around fixed point
two polarising filters at right angles
no light gets through
partial polarisation of light
when reflected off certain surfaces
uses of polarisation polaroid cameras
photos of objects underwater
intensified colour, reduced glare
light from underwater refracted, object more intense
uses of polarisation sun glasses
block partially polarised light
horizontal blocked, vertical passes through
uses of polarisation other
stress analysis
transmitters
microwave ovens
radiowaves
10^3 m
10^4 Hz
microwaves
10^-2 m
10^8 Hz
infrared
10^-5 m
10^12 Hz
visible light
10^-6 m
red longest wavelength
uv
10^-8 m
10^15 Hz
x-ray
10^-10 m
10^16 Hz
gamma
10^-12 m
10^20 Hz
superposition
2 waves occupying the same physical space
resultant wave
total of a wave= sum of displacement of other waves
constructive interference
phase difference 0,360
n wavelengths
destructive interference
180
n+1/2 wavelengths
coherence
fixed/constant phase relation
same of frequency and wave length
effect of increasing wavelength diffraction gratings
width of central maxima increases
diffraction effects increase
intensity decreases
1000 slits per m
s = 1/1000
diffraction gratings sinθ must be
less than 1
increasing wavelength effect on sinθ
increases
increasing distance effect on sinθ
decreases
laser safety
body’s natural aversion reflex too slow to prevent damage to retina
demonstrating stationary waves
powder in tube of air
microwaves
stationary wave
superposition between two progressive waves travelling in opposite directions in the same space
progressive waves vs stationary waves
progressive: all same amplitude, in phase, energy transferred along wave, no nodes or antinodes, speed=speed which wave moves through medium
standing: different amplitude depending on superposition, points between nodes in phase, energy stored, each point on waves oscillates at different speed, doesn’t move
nodes
zero displacement, fixed
minimum energy
antinodes
maximum displacement
maximum energy
move in vertical direction
harmonics in closed tube
starts at 1/4λ
every 1/2
harmonics in open tube
starts at 1/2 λ
every 1/2
harmonics in tubes
node formed at closed end
Young’s double slit experiment
coherent sources
monochromatic light
waves diffract, superpose
constructive interference bright fringes
destructive interference dark fringes
central maxima greatest intensity
W= λD/s
W= fringe spacing
s= slit spacing
D= distance from slit to screen
white light double slit
central fringe= bright white light
all fringes more spread out
side fringes have spectrum of visible colours
blue diffracts less, closer to centre
increasing slit width
decreases the width of central maxima as diffraction increases
intensity of central maxima increases
more slits
sharper pattern
use of diffraction gratings examples
proves light is a wave
exocrystallography -> atom spacing via diffraction (X-rays)
finding unknowns separate wavelengths from different substances
used in white fibre optics to separate signals
astronomy measuring light from celestial bodies to identify chemical make up
high pitch
high frequency
high volume (loud)
high amplitude
diffraction derivation
1st order maxima happens when path difference = 1λ
similar triangles
distance= d
order of central maxima
zero
2nd harmonic
1st overtone
nair
1
nwater
1.3
nglass
1.5
resonance
system made to oscillate at its natural frequency
stationary waves practical
measure mass (per unit length), length, tension
T=mg
you can calculate any of these 3
mass -> change material
length-> move oscillator
tension -> change hanging masses
longer string
lower resonant frequency
larger mass per unit length
lower resonant frequency
higher tension
higher resonant frequency
first harmonic
fundamental
1/2λ
critical angle
n1 > n2
sin90 = 1
n2/n1
θ1 > θ2
total internal reflection
fibre optics
step index
core surrounded by cladding with lower refractive index (+small critical angle)
narrow
light always hits barrier at angle greater than critical angle
increasing bandwidth of available light
pulse absorption
energy absorbed by medium
loss in amplitude
counteract by signal boosting
pulse broadening
modal -> different wave lengths reach the end at different points
material -> different paths through material
resulting in degraded signal
modal dispersion prevention
use monochromatic light
material dispersion prevention
monomodefibre
as narrow as possible
