Waves Flashcards
speed of light
c = 3 x 10^8 m/s
speed of sound
343 m/s
wavelength frequency speed
v = fλ
frequency, time period
T = 1/f
Polarization
waves of the transverse waves are limited to one plane of movement, while the rest is absorbed
polarising filters what they do
only waves oscillating in same direction as filter will pass through
2 filters perpendicular to each other won’t let through any light
uses of polarisation
- polarised sunglasses to reduce glare
- receiving areal and radio signals
stationary waves nodes and antinodes
node - no displacement
anti-node - point of max displacement
distance between two nodes
1/2 λ
Explain how standing wave is formed (3)
- superposition
- two waves of same frequency and amplitude
- travelling in opposite directions
- one is reflected
points between two nodes
points between two nodes all in phase
For first harmonic:
frequency, length, tension, μ
For first harmonic:
f = 1/2L sqrt(T/μ)
where μ is mass/length of string
standing wave with microwave practical setup
transmitter
metallic reflective plate 1/2λ away
movable detector in middle
when detector is at plate, min
when at middle, max
standing wave in a tube
at closed end: pressure antinode, displacement node
at open end: pressure node, displacement antinode
laser
monochromatic light (one wavelength) so light is coherent
double slit setup and result
laser which has similar wavelength to gap
result is equally spaces fringes
single slit diffraction monochromatic
large central maxima with smaller less intense fringes on either side
single slit diffraction white light
- central maxima bright white
- less wide less intense fringes on either side
- fringes on either side would be spectrum which get more and more spread out
- violet closest to maxima, red furthest
diffraction
the spreading out of waves as they pass through a gap or around an obstruction
single slit equation (destructive min)
dsin(θ) = mλ
where d is the slit width
m is the order of the min
double slit equation
W = λD/s
where w is fringe spacing
D is from slits to screen
s is slit spacing
diffraction grating equation and derivation
dsin(θ) = nλ
where d is the slit width
n is the order of the bright spot
derive on paper
snells law
n1sin(θ1) = n2sin( θ2)
refractive index, speed of light
n = c in air/ c in material
critical angle
angle of incidence when angle of refraction = 90
above which total internal refraction happens
show c, n1, n2 equation
n1 sin θ1 = n2 sin θ2
n1 sin θc = n2
sin θc = n2/n1
uses of total internal reflection
optic fibres
step index optic fibre
the refractive index of each component increases moving from the outside to the centre of the fibre
role of cladding in optic fibre
- Protect the thin core from damage and scratching
- Prevent signal degradation through light escaping the core, which can cause information from the signal to be lost
- It keeps the core separate from other fibres preventing information crossover
prisms
prisms will always totally internally reflect
approx λ for em waves
Radio waves - 1km
Microwaves - 10 cm
Infrared - 10^-5
Visible - 10^-6
Ultraviolet - 10^-8
X rays - 10^-10
Gamma - 10^-12
coherent (waves)
have same wavelength, frequency and are in phase
stationary wave experiment
- signal generator connected to vibration transducer
- string going across a pulley at end of bench with a mass hung on one end
- measure mass and length of string to find μ
- find tension
- vary frequency of signal generator until first harmonic
equation
2 reasons for signal degradation and effects on signal
- absorption by material causes loss in amplitude
- dispersion causes broadening
Two types of dispersion (signal degredation)
- modal - light enters at different angles
- material - not all light had same wavelengths
diffraction grating limitations (from equation)
d sin(θ) = nλ
sin(θ) can’t be greater than 1
so only certain values of n order possible
