4.4.1 Progressive Waves Flashcards
What are the approximate wavelengths for:
Radio waves
Microwaves
Infared
Visible light
10^-6 - 10^-1
1-0^-1-10^-3
10^-3 - 4x10^-7
4x10^-7 - 7x10^-7
What are the approximate wavelengths for:
Ultraviolet
X-Rays
Gamma Rays
7x10^-7 - 10^-8
10^-8 - 10^-13
10^-10 - 10^-16
summarise the properties of:
transverse waves
longitudinal waves
transverse:
- oscillations perpendicular to propagation of energy transfer
- has peaks & troughs
longitudinal:
- oscillations parallel to propagation of energy transfer
- has compressions & rarefactions
define:
period
frequency
and provide an equation relating them
period: time taken for one full oscillation to pass a given point
frequency: number of oscillations passing a given point per unit time
F=1/T
explain how to determine frequency
- feed an oscilloscope a signal
- set time-base on x axis for time, y axis for amplitude
- measure time taken for one oscillation and calculate frequency
define & explain:
reflection
refraction
reflection:
- direction changes between boundary of two media, remains in original medium,
- Θincidence=Θreflection, wavelength & frequency unchanged
refraction:
- direction and speed change, enters new medium, frequency unchanged
- soundwaves ^ in denser media, EM waves v
partial reflection at boundary
define & explain:
diffraction
polarisation
diffraction:
- wave front spreads through gap, wavelength and frequency unchanged, max diffraction -> gap size = wavelength
polarisation:
- oscillation is restricted to one plane, only occurs in transverse waves
recall how to demonstrate wave effects with polarising filters
place two polarising filters on top of one another, one rotated 90deg, light intensity v, all light polarised
recall how to demonstrate wave effects with a ripple tank
adjust depth to show refraction, add a slit to show diffraction
recall how to demonstrate wave effects with metal grilles
microwave transmitter & receiver on opp. sides of grille, vertical grille = max signal, horizontal = min signal (polarisation?)
define the intensity of a progressive wave and relate it to amplitude
intensity = the radiant power passing at right angles through a surface per unit area
intensity is directly proportional to the amplitude squared
provide some properties of electromagnetic waves
- they are transverse, progressive waves
- they consist of magnetic and electric fields oscillating at right angles to each other
- they all travel at a speed of 3.00x10^8 ms^-1 in a vacuum
explain the refraction of light, and how to find the angle of refraction
- the speed of light changes as it enters a new medium
- the refractive index (n) can be used to find the angle of refraction
- n=c/v, n1sinΘ1=n2sinΘ2
explain total internal reflection
- light is reflected back into it’s original media
- the first material must have the higher n
- the Θ of incidence > critical angle
- sinC=1/n
- original material must be air
define superposition
- 2+ prog waves overlap to form a single wave
- when two waves meet at a point the resultant displacement = the sum of the displacements of the two waves at that point
compare constructive and destructive interference
constructive interference: displacements in same direction, path diff = nλ
destructive interference: displacements in opposite direction, path diff = (n+1/2)λ
define phase difference and coherence
- the difference in degrees or radians between the same point on two wave cycles
- waves with a constant phase difference
explain how to investigate superposition & wavelength with sound waves
- connect two speakers to one oscillator in line with each other
- walk in front of them slowly
- loud sound = maximum = path diff is λ
- quiet sound = minimum = path diff is λ/2
explain how to investigate superposition & wavelength with a laser
- shine laser through two slits approx. the same size as wavelength
- the slits act as two coherent point sources
- an interference pattern will form
- x=λD/a
- x = fringe spacing, D= distance from screen, a= slit spacing
(for x measure several fringes/number of spacings)
explain how to investigate superposition & wavelength with microwaves
- attach two microwave transmitter cones to one signal generator
- move a receiver probe along a straight line parallel to the generator
- you will get an alternating pattern of strong/weak signals
explain diffraction gratings
- diffraction grating produces sharper lines
- therefore the interference pattern is a lot sharper
- there is a maximum brightness at the centre (zero order line)
- lines on either side = first order, carrying on outwards
dSinΘ=nλ
d=slit spacing, Θ= angle between first & zero order line
Θ=x/D
x= fringe width, D= dist. between grating & screen
explain what happens when you put white light in a diffraction grating
- spectra are produced
- zero order = white
- other orders = spectrum, with violet on the inside
