waves Flashcards
what are some applications of polarisation?
polaroid sunglasses
TV and radio signals
what happens when two waves meet and have equal but opposite displacements?
destructive interference
what is superposition?
where the displacements of two waves are combined as they pass each other
when does constructive interference occur?
when two waves have displacement in the same direction
when is a stationary wave formed?
formed from the superposition of 2 progressive waves,
travelling in opposite direction in the same plane,
with the same frequency, wavelength and amplitude
is energy transferred by a stationary wave?
no
what is another name for the lowest frequency at which stationary waves form?
the first harmonic
what is the distance between adjacent nodes (or antinodes)
half a wavelength
what is path difference?
the difference in the distance travelled by two waves
the difference in distances travelled from two coherent sources to an interference fringe
what are 3 properties of a coherent light source?
it has the same frequency and wavelength
and a fixed phase difference
why are lasers used in diffraction experiments
they form clear interference patterns
are lasers coherent?
yes
what are some safety precations when using lasers
wear laser safety goggles
don’t shine the laser at reflective surfaces
display a warning sign
never shine lasers at a person
what does Young’s double slit experiment provide evidence for?
wave nature of light
what does diffraction and interference of light provide evidence for?
wave nature of light
what is diffracion?
the spreading out of waves when they pass through or around a gap
what would be observed if white light was diffracted
a spectrum of colour in the diffraction pattern
which colour is furthest from the central white maximum in the diffraction of white light
red
which colour is closest to the central white maximum in the diffraction of white light
violet
What can be varied to change the width of the central diffraction maximum?
slit width and wavelength
what is a diffraction grating?
a slide containing many equally spaced slits very close together
when can total internal reflection (TIR) occur?
when the angle of incidence is greater than the critical angle and the incident refractive index is greater than the refractive index of the material at the boundary
name an application of TIR
optical fibres
describe the optical densities of parts of an optical fibre
optically dense core
surrounded by a less optically dense claddding
What is useful about the cladding in optic fibres
allows TIR to occur
protects core from damage
prevents signal degradation / information loss (through light escaping the core)
what is phase difference?
what is it measured in?
in radians,
for two objects oscillating in the same time period, T p.d. = 2pi Δt /T
delta t is the time between successive instants when the two objects are at maximum displacement in the same direction
what is a node?
a fixed point in a stationary wave pattern where the amplitude is zero
what is modal dispersion?
the lengthening of a light pulse as it travels along an optical fibre, due to rays that undergo less total internal reflection
what is defined as ‘the lengthening of a light pulse as it travels along an optical fibre’?
modal dispersion
