Waves Flashcards
define amplitude
waves maximum displacement from the equilibrium position
define frequency
number of complete oscillation past a fixed point per second
define wavelength
Length of one oscillation
what is phase
position of a certain point in the wavecycle measured in degrees or radians
what is Time period
time taken for one full oscillation
what is a progressive wave
made up of a medium that oscillates in order to transfer energy without transferring matter
what are the high and low pressure areas in a longitudinal wave called
compressions and rarefactions
what does it mean if two waves are in phase
what properties need to be the same
The two waves reach there maximum and minimum values of displacement at the same time
they must have the same frequency
what is the phase difference of two in phase waves
2π
what does it mean if two points on the wave cycle are exactly out of phase
Phase difference of π
- one wave will have a maximum peak at the same instant the other with have minimum peak
what does a polarizing filter do
only allows oscillations in one plane
What types of waves can be polarized
Transverse waves
what provides evidence for the nature of transverse wave
Polarization
only waves which oscillate perpendicular to direction of travel can be polarized therefore if provides evidence that transvers waves oscillate perpendicular
what is an example of a polaroid
Sunglasses
how is polarization used in broadcasting
TV/Radio waves are plane polarized by transmitting areal therefore receiving areal must be in the same plane to receive signal at full strength
what is Superposition
The vector sum of displacements of waves are combined when they pass over each other
what are Coherent waves
Waves that have a constant phase relationship overtime
the must have same frequency and wavelentgh
what is constructive interference
what is perfect constructive interference
when two waves that have displacement in the same direction superimpose meaning the resulting amplitude is greater.
perfect constructive interference is when two coherent (same frequency and wavelength) waves with phase difference of 2π superimpose
what is destructive interference
what is perfect destructive interference
Occurs when two waves with displacement in opposite directions superimpose
when two coherent waves with a phase difference of π superimpose
What is a stationary wave
formed when two progressive waves travelling in opposite directions with the same frequency wavelength and amplitude superimpose
how much energy is transferred via a stationary wave
0
what is an antinode
Point on a stationary wave with maximum displacement. Constructive interference occurs
what is a node
Point on a stationary wave where displacement is zero
destructive interference occours
how can you make a stationary microwave
- Aim microwaves at metal plate and use microwave detector to detect position of antinode and nodes
How can a stationary sound wave be produced
- Place a speaker at the end of a closed glass tube and laying powder along the bottom of the tube
- powder is shaken at the antinodes and will settle at the nodes
what is path difference
difference in distance travelled by two waves from there source
what does in phase mean in context of velocity and displacement
on a single wave, when too waves are in phase they are at the same point in the wave cycle therefore will have the same displacement and velocity
what is refraction
Light enters a different medium causing a change in direction and speed
what is the equation for refractive index
n = speed of light in vacuum / speed of light in substance
what is diffraction
spreading out of waves as they pass through or around a gap
what is a diffraction grating
slide containing lot of equally spaced slits very close together
what happens when monochromatic light is diffracted through a single slit
diffraction pattern of bright central fringe double the width of the other fringes
what happens when monochromatic light is passed through a diffraction grating
interference pattern of alternating bright maxima and dark minima.
what is the difference between interference patterns of single slit and diffraction grating
for diffraction grating:
- intensity is much greater
- there isn’t as much of a fall in intensity as orders of maxima increase
what effect does varying the slit width have of double and single slit diffraction pattern
- Reducing slit width:
central maxima decreases intensity and become wider - increasing slit width
central maxima becomes narrower and increases in intensity
what happens when white light is passed through a single slit
Central white maxima double the width of any other maxima with alternating dark and light fringes with violet closest to center and red furthest away
what happens as wavelength increases in a diffraction grating experiment
distance between maximas increases
what is a coherent light source
emits light with constant phase difference over time (same frequency and wavelength)
what is monochromatic light source
A light source that only emits a small range of a fixed wavelength
example of a coherent monochromatic light source
lazer
why are lazers used in experiments
they create a clear interference pattern and are precise
what was Youngs Double slit experiment
Coherent monochromatic light shone through a double slit creating a diffraction pattern
how are maxima’s and minima’s created in the diffraction pattern
at maxima’s light interferes constructively
at minima light interferes destructively
how can you make sure light is monochromatic in YDS experiment
- use laser
- use filter
- shine light through single slit before Double slit
when can the YDS experiment formula be used
when Distance between screen and slits is a lot greater than the slit separation
what does YDS experiment give evidence for.
Wave like nature of light
- only waves can superimpose constructively and destructively
what safety precautions must be taken when dealing with lasers
safety goggles
sign
no reflective surfaces
What is a useful application of TIR
optical fibres
when does TIR occour
when n1>n2
and when angle of incidence is greater than the critical angle
describe the structure of an optical fiber
optically dense core surrounded by less optically dense cladding allowing TIR
what is the purpose of cladding
- protection
- allowing TIR which prevents signal degradation
what is the critical angle
angle of incidence where the angle of refraction is π/2
how could you create a interference pattern using soundwaves
tow speaker connected to the same signal generator.
intensity of waves and location of maxim and minima can be measure using a microphone
what are the two type of signal degradation in optical fibres
Absorption
Dispersion
describe absorption
where part of the signals energy is absorbed leading to loss in amplitude and loss of information
what are the two types of dispersion
modal and material dispersion
what is material dispertion
how can it be prevented
material dispersion is caused by using lights of different wavelengths therefore they travel at different speeds leading to pulse broadening
can be prevented by using monochromatic light
what is modal dispersion
how can modal dispersion be reduced
- light enters fiber at different angles therefore changes total distance travelled by light rays leading to pulse broadening
- making the core very narrow
how can both dispersion and absorption be solved
using a signal repeater
explain evidence that suggests that electron beams act as waves when diffracted
- There is an interference pattern (like light) with maxima’s and minima’s
- the pattern follows the formula nλ=dsinθ
- if particles didn’t act as waves there would be random scattering and one bright spot in the center
in terms of phase, what points on a stationary wave are in phase or antiphase
points between nodes are in phase
points with an odd number of nodes between them are out of phase/antiphase
points that have an even number of nodes between them a in phase
