waves Flashcards
what is a wave
an oscillation of particles or fields
what is a progressive wave
A progressive (moving) wave carries energy from one place to another without transferring any material.
what is a cycle of a wave
one complete vibration of the wave
what is wavelength
Wavelength, l, metres — the length of one whole wave cycle, from crest to crest or trough to trough.
what is the time period of a wave
Period, T, seconds — the time taken for a whole cycle (vibration) to complete, or to pass a given point.
what is the frequency of a wave
Frequency, f, hertz — the number of cycles (vibrations) per second passing a given point.
what is the phase of the wave
Phase — a measurement of the position of a certain point along the wave cycle.
what is the phase difference of a wave
Phase difference — the amount one wave lags behind another.
what is reflection of a wave
Reflection — the wave is bounced back when it hits a boundary
what Is refraction a wave
Refraction — the wave changes direction as it enters a different medium. The change in direction is a result of the wave slowing down or speeding up.
frequency equation
f = 1/ T
how to work out the wave speed
wave speed = distance travelled/ time taken
how to work out speed of a wave
speed of wave = wavelength x frequency
what is the speed of a em wave in a vacuum
c = 3.00 × 108 ms–1
what are transverse waves
waves with vibrations perpendicular to the direction of energy transfer.
give an example of a transverse wave
em waves
what are longitudinal waves
waves with oscillations parallel to the energy transfer
give an example of a longitudinal wave
sound waves
what is polarisation
when vibrations are restricted to one plane
what waves can you polarise
transverse waves
what is evidence that electromagnetic waves are transverse
polarisation
how can you polarise waves
using a polarising filter
if you have two polarising filters at right angles to each other what happens
no light will get through
how do polaroid glasses work
Polaroid sunglasses reduce the glare of light reflected by water or glass. The reflected light is polarised and the intensity is reduced when it passes through the polaroid sunglasses.
why are the rods on a tv aerial horizontal
TV signals are polarised by the orientation of the rods on the broadcasting aerial. To receive a strong signal, you have to line up the rods on the receiving aerial with the rods on the transmitting aerial — if they aren’t aligned, the signal strength will be lower.
what is superposition
the instant the waves cross, the displacements due to each wave combine. Then each wave moves on
what is the principle of superposition
when two or more waves cross the resultant displacement equals the vector sum of the individual displacements
a crest pus a crest and a trough plus a trough is a example of what
constructive interference
a crest plus a trough is an example of what
destructive interference
for interference to be noticeable what should be true about the amplitudes
the amplitudes should be nearly equal
what does it mean if two points are in phase
if they are both at the same point in the wave cycle
what is true about the points displacement and velocity if the points are in phase
same displacement and velocity
what angle should you use to show 1 complete cycle of a wave
360 or 2 pi
how do you know two points are in phase
the have a phase difference of zero or a multiple of 360
how do you know two points are exactly out of phase
have phase difference of odd number multiples of 180
how can you get a clear interference pattern
the two or more sources must be coherent and be in phase
what does it mean to be coherent
to have the same wavelength and frequency and a fixed phase difference between them
what does getting a constructive or destructive interference at a point depend on
how much further one wave travelled that the other wave to get to that point
what is path difference
The difference in distance travelled by two waves from their sources to the point where they meet
when will you get constructive interference
At any point an equal distance from two
sources that are coherent and in phase or where the path difference is a whole number of wavelengths.
where do you get destructive interference
But at points where the path difference is half a wavelength, one and a half wavelengths, two and a half wavelengths etc., the waves arrive out of phase and you get destructive interference.
when do you get constructive interference (equation)
path difference = nλ
where do you get destructive interference (equation)
path difference + (2n + 1)λ /2
what is a stationary wave
superposition of two progressive waves with the same frequency (wavelength), moving in opposite directions.
what happens with stationary waves that doesn’t happen with progressive waves
no energy is transmitted
what are nodes
where amplitude is zero
what are antinodes
points of maximum amplitude
what is diffraction
the way waves spread out as they come through a narrow gap or go around obstacles
what does the amount of diffraction depend on
depends on the wavelength of the wave compared to the size of the gap
what happens to the diffraction when the gap is a lot bigger than the wavelength
diffraction is unnoticeable
what happens to diffraction when you have a gap several wavelengths wide
you get noticeable diffraction
what happens to diffraction when the size of the gap is roughly the same size as the wavelength
you get the most diffraction
what happens to diffraction if the size of the gap is smaller than the wavelength
no diffraction an the waves are mostly reflected back
to get a clear diffraction pattern for light what do you need to do
use a monochromatic coherent light source
what does monochromatic mean
the light has all the same wavelength so its the same colour
what is an example of a monochromatic coherent light source
lasers
what happens you shine light through a narrow slit
you get a diffraction pattern that has a central bright fringe with dark and bright fringes alternating on either side where the bright and dark fringes are created by destructive and constructive interference
what happens when you diffract white light through narrow slit
you get a diffraction pattern of a central bright white fringe where the fringes are a spectra of colours with blue on the inner side and red on the outer side and fringes getting fainter the further you move outwards
why do you get that specific diffraction pattern for white light when shone through a narrow slit
because white light is a mixture of colours each with different wavelengths so when diffracted all the wavelengths are diffracted by different amounts
what happens to central maximum if you decrease slit width
you decrease the amount of diffraction and so the central maximum is narrower and the intensity of the central maximum is higher
