Waves Flashcards
define a progressive wave
A moving wave that carries energy from one place to another without transferring any material in which the direction of energy transfer is the same as the waves direction of travel
def phase difference
The amount that one wave lags behind another
What is the equation for frequency in terms of the period?
Frequency = 1 / Period
How does an oscilloscope work?
A cathode ray oscilloscope measures voltage. It displays waves from a signal generator as a function of voltage over time.
What is the name of the wave on an oscilloscope?
A trace
What are the squares on an oscilloscope called?
Divisions
What is the timebase on an oscilloscope?
The horizontal axis is the timebase (the amount of time per division)
How would you calculate wave frequency from an oscilloscope?
Find the period by counting how many divisions in one full oscillation of the wave and then multiply by the timebase. Then do 1 / Period to get frequency.
What two dials are on an oscilloscope and can help make them easier to read?
The gain dial (changes volts/div) and the timebase dial (changes time(ms)/div)
What direction do transverse waves vibrate with respect to the direction of movement?
At right angles to the direction of movement
What direction do longitudinal waves vibrate with respect to the direction of movement?
Parallel to the direction of movement
What is the name for the points on a longitudinal wave where the waves are close together and far apart?
Compression (close) and rarefaction (far)
How can you identify the wavelength of a longitudinal wave?
From one compression/rarefaction to another
Define the intensity of a wave
Intensity is the rate of flow of energy per unit area at right angles to the direction of travel of the wave
What is the equation and unit for wave intensity?
Intensity (W/m^2) = Power (W) / Area (m^2)
Intensity is proportional to…
Amplitude squared
What types of fields are the waves on the EM spec
Electrical and magnetic
Can EM waves be polarised?
Yes, since they are all transverse
What is the full EM spec?
Radio, Micro, Infrared, Visible light, Ultraviolet, X-Ray, Gamma
What is the approximate wavelength of radio waves? (m)
10^-1 - 10^6
What is the approximate wavelength of microwaves? (m)
10^-3 - 10^-1
What is the approximate wavelength of infrared light? (m)
7x10^-7 - 10^-3
What is the approximate wavelength of visible light? (m)
4x10^-7 - 7x10^-7
What is the approximate wavelength of ultraviolet light? (m)
10^-8 - 4x10^-7
What is the approximate wavelength of X-rays? (m)
10^-13 - 10^-8
What is the approximate wavelength of gamma rays? (m)
10^-16 - 10^-10
What are some uses of radio waves? (1)
Radio transmmissions
What are some uses of microwaves? (3)
Radar, cooking, TV transmissions
What are some uses of infrared light? (4)
Heat detectors, night vision cameras, remote controls, optical fibers
What are some uses of visible light? (2)
Human sight, optical fibers
What are some uses of ultraviolet light? (2)
Sunbeds, security marks
What are some uses of X-rays? (3)
Medical imaging, Airport security scanners, radiotherapy (cancer treatment)
What are some uses of gamma rays? (3)
Irradiation of food, sterilization, radiotherapy (cancer treatment)
What can radio waves penetrate through?
Matter
What can microwaves penetrate through?
Mostly matter, but causes heating
What can IR light penetrate through?
Absorbed by matter but causes heating
What can visible light penetrate through?
Absorbed by matter but causes heating
What can UV light penetrate through?
Absorbed by matter but causes some ionisation
What can X-rays penetrate through?
most matter but causes ionisation
What can gamma rays penetrate through?
most matter but causes ionisation
def polarisation
The filtering of transverse waves so that they only pass through a filter if they oscillate in one direction (are able to pass through the filter)
def the plane of polarisation
The plane which a polarised wave oscillates on (a vertical filter polarises a wave in the vertical plane)
def plane polarisation
When a wave is polarised to only oscillate in one direction
What does the fact that you can polarise light show that light is?
It shows that light is a wave (or rather behaves like one)
What is the transmission axis of a polarisation filter?
Only light oscillating along the transmission axis will pass through (Waves oscillating vertically will be transmitted through a vertical transmission axis)
What can you use to polarise microwaves?
A metal grille (microwaves have too high a wavelength to be polarised through a polarisation filter)
What determines how much waves diffract through a gap?
The size of the gap and the wavelength of the travelling wave.
At what point can you observe the most diffraction when changing the size of the gap in an experiment?
When the size of the gap is the same as the wavelength of the travelling wave.
What happens if the size of a gap for diffraction is smaller than the wavelength?
The waves get reflected back on themselves
Why can you hear someone round a doorway but not see them?
Sound waves have similar wavelengths to the size of doorways and so diffract a lot but light waves are far too small to cause noticeable diffraction
What two experiments could you do to show light diffracting?
Shine a laser through a very small slit or shine white light through a colour filter.
def reflection
When a wave is bounced back upon hitting a boundary where the angle4 of incident is equal to the angle of reflection.
def refraction
The change in the direction of movement of a wave as a result of entering a different medium.
Why does the wave speed change during refraction?
The wavelength changes but the frequency remains constant.
def optical density
The amount that a material slows down light. A higher optical density means light travels slower through it.
what is the equation for refractive index?
n (refractive index) = c (sol in a vacuum) / v (sol in that material)
What is Snell’s law
n1sinA1 = n2sinA2
def total internal reflection
When all of the light is reflected back into the material and not refracted
What is a critical angle? (refraction)
The angle at which light stops being refracted and is only internally reflected if it gets any larger
What is the equation for the critical angle for light within a material to air boundary?
SinC = 1/n
def superposition
When to waves cross, the displacement as any point is the sum of the two individual displacements
def interference
When two or more waves superimpose with each other
def constructive interference
When waves ‘combine’ to increase the original displacement. i.e. a crest and a crest or a trough and a trough
def destructive interference
When two waves superimpose at a point to create nothing i.e. a crest ‘combines’ with a trough of equal size and results in 0 displacement
what does it mean if interference isn’t ‘total’?
The two parts of the waves are not of equal magnitude and so don’t completely cancel out or completely double in displacement.
def ‘in phase’
two points on a wave are in phase if they are at the same point of the wave cycle i.e. two crests
what property to points that are in phase have?
The same displacement and velocity
def phase difference?
The difference in position (x-axis) of two points
def coherence
When two waves have the same wavelength and frequency and a fixed phase difference
def path difference
For two wave sources that are in phase and coherent, the path difference is just how much further one wave has travelled compared to another to get to that point.
At what amount of path difference can you observe constructive interference?
When the path difference is a whole number of wavelengths
At what amount of path difference can you observe destructive interference?
When the path difference is an odd number of half wavelengths.
What is the equation for wavelength that links fringe spacing and the distance from a slit to a screen?
λ = (a (slit separation) * x (fringe separation)) / D (distance from slits to screen)
What effect does diffracting through more than two slits have in comparison to diffracting through only two slits?
The fringes are brighter and more defined (narrower).
When shining light through a diffraction grating, what effect does a longer wavelength light cause?
The pattern will be more spread out
What happens when white light is shone through a diffraction grating?
Each maxima (order) is a spectra from red on the outside (side furthest from central maxima) and violet on the inside (side closest to central maxima)
Do stationary waves transmit energy?
Nuh uh
How is a stationary wave formed when only one signal generator is present?
The waves generated travel out and then reflect back perfectly to create a standing wave
On a standing wave, where are the nodes and where are the antinodes?
Nodes are where the waves meet, antinodes are where the waves are at a greatest distance.
Define resonant frequency in terms of a number of wavelengths.
In order to achieve a resonant frequency, an exact number of half wavelengths fit into the space that a wave has to oscillate. Or in the string experiment, an exact number of half wavelengths fit onto the string.
If a tube is open at both ends and a standing wave is within it, what type of node would be at each end?
Antinode
If a tube is closed at both ends and a standing wave is within it, what type of node would be at either end?
Node
