waves Flashcards
how is a stationary wave formed
a wave is reflected causing 2 waves to travel in opposite directions with the same speed, frequency, and similar amplitude. a resultant wave is produced as a result of when the 2 waves superposition. total constructive interference at anti-nodes, maximum displacement. total deconstructive interference at nodes, minimum displacement
do stationary (standing) waves transfer or store energy
store energy. no energy is transferred
are stationary (standing) waves in phase or out of phase
in phase
real life applications of standing (stationary) waves?
musical instruments - formation of harmonics
telecommunications - used in antennas to maximise signal strength and minimise interference
medical imaging - used in ultrasound for images of internal organs
define coherence
sources are coherent if they maintain a fixed phase difference
define progressive wave
transmits energy
what is a critical angle
the angle of incidence causing the angle of refraction to be 90
what is total internal reflection
occurs inside a medium when a ray reflects back in
happens when angle of incidence larger than critical angle
what do fibre optics do
transmit information via light signals and total internal reflection
what are fibre optics made of
a core surrounded by cladding
made of glass or plastic
what does cladding in fibre optics do
protect the core from damage
prevents signal degradation = light escaping causing information to be lost
example of transverse wave
all electromagnetic
string
water
example of longitudinal wave
sound
ultrasound
what is signal degradation
when light escapes the optical fibre causing loss of information
causes of signal degradation
absorption
dispersion
what is absorption in an optical fibre
when some energy from the signal is absorbed by the fibre, decreasing its amplitude, losing some information
what is dispersion in an optical fibre
dispersion causes pulse broadening which is when the received signal is broader than the original transmitted signal
broader signals can overlap so lose information
what are the 2 types of dispersion
modal dispersion
material dispersion
what is modal dispersion
when the light rays enter at different angles, so different paths, so different times to travel, causing pulse broadening
what is material dispersion
when light rays are of different wavelengths, so different times to travel, causing pulse broadening
how can modal dispersion be reduced
have the core of the fibre narrower so less difference between path taken
how can material dispersion be prevented
use monochromatic light (light of one wavelength)
how can both material and modal dispersion be reduced
use an optical fibre repeater
it regenerates the signal during travel
define longitudinal waves
oscillations are parallel to the direction of energy transfer
made of compressions and rarefactions
define transverse waves
oscillations are perpendicular to the direction of energy transfer
what is a polarised wave
a wave that has oscillations that only travel in one plane
only transverse waves can be polarised
how to be safe when using a laser
dont shine at person
dont shine at reflective materials
wear laser safety goggles
display warning sign
what is the path difference of two waves when constructive interference occurs
nλ where n is an integer
what is the path difference of 2 waves when destructive interference occurs
n+1/2 λ where n is an integer
what is a diffraction grating
slide which has hundreds of slits per millimetre
uses of a diffraction grating
x-ray crystallography
finding elements in stars
how can the width of the central maxima in an interference pattern be changed
slit seperation
wavelength of light
what does increasing slit separation do
decrease amount of diffraction that occurs, so make central maximum narrower and increase intensity
what does increasing wavelength do
increase amount of diffraction that occurs because wavelength closer to size of slit, make central maximum wider and decrease intensity
what does the interference pattern of white light look like
central maximum is white, with alternating light and dark besides it
violet is closest to the central maximum
red is furthest away from the central maximum because longest wavelength so diffracts more
what experiment proves the wave nature of light
young’s double slit experiment
how fast do electromagnetic waves travel in a vacuum
3x10^8 m/s
lasers produce c___ and m____ light
coherent and monochromatic
what does coherent light mean
same frequency, wavelength, phase difference
