Waves Flashcards
What is the definition of amplitude?
The maximum displacement from the zero point.
Define wavelength.
The distance between two points with the same phase.
What is the definition of period?
The time for one complete cycle.
Define frequency.
The number of complete oscillations per second.
Give frequency in terms of C and wavelength.
Frequency = C/Wavelength.
Define a Transverse wave.
A wave in which, the oscillations are perpendicular to the direction of movement of the energy/information.
Define a Longitudinal wave.
A wave in which, the oscillations are parallel to the direction of movement of the energy/information.
Define a wave.
A way to move energy or information from one point to another, in a medium, without the medium moving between those points.
What is the law of superposition?
When two similar waves meet at the same point, the resulting displacement is the vector sum of the individual displacements.
What is more energetic, red light or blue light?
Blue light > ultraviolet > Xrays > Gamma rays
Do radio waves have a high or low frequency/wavelength?
Radio, micro and infra red have a high wavelength and a low frequency.
Do Gama rays have a high or low frequency/wavelength?
Gama, X ray and ultra violet have a low wavelength and a high frequency.
What are the audible spectrum limits?
below 20Hz is subsonic and above 20,000Hz is UltraSonic.
Define Reflection.
When a wave bounces off the boundary between one material and another.
What is the Law of reflection?
I = r
What is the Law of refraction?
(n1)Sin(O1) = (n2)Sin(O2)
How do we find “n”
n = speed of light in vacuum/speed of light in material.
Does light take the path of shortest time or distance?
Light takes the path of shortest time.
When does total internal reflection occur?
when the angle of incidence is bigger than the critical angle.
How do we find the critical angle?
(n1)Sin(critical angle) = 1
Two waves intersect with a phase difference of 0*, what interference occurs?
Constructive interference.
Two waves intersect with a phase difference of 180*, what interference occurs?
Destructive interference.
When do beats occur?
Two Waves
Same Direction
Slightly different phase
What is phase?
Phase is the difference in position of one wave to another- ie how far one peak is from another on a different wave.
What is the fundamental frequency of a Node Node or antinode antinode standing wave? (an open pipe)
f = V/2L
What is the nth harmonic of a Node Node or antinode antinode standing wave? (an open pipe)
f = nV/2L
What is the fundamental frequency of a Node Antinode standing wave? (a closed pipe)
f = V/4L
What is the (2n-1)th harmonic of a Node Antinode standing wave? (a closed pipe)
f = (2n-1)V/4L
When is the point of maximum diffraction?
When the wavelength = gap size
What is the equation for “just resolving”
wavelength/hole width = width of two objects/distance the two objects are away from the hole
what does double slit detraction look like?
a wide single slit diffraction envelope with interference peaks within it.
What is the equation for multislit defraction?
(nth Maxima)(wavelength of light) = (distance between slits)(sin(angle of nth Maxima))
What is the equation for multi slit diffraction?
(peak number)(wavelength) = (distance slits are apart) sin(theta)
what is the difference in meaning for “n” in the single and multi slot diffraction equations?
single slit - n = trough number
multislit - n = peak number
define coherence
two waves are coherent if the phase difference between them is constant
what does Young’s slit experiment show us?
it shows us the wave nature of light
how does slit width effect multislit diffraction pattern?
as the slit width increases, the angle of the first trough of the envelope decreases.
when using a diffraction grating, how do you find the distance between the slits?
distance between slits = 1/ slits per mm
what happens as we add the number of slits in multislit diffraction?
the peaks all get sharper
what is a missing Maxima in regards to multislit diffraction?
whan a peak of the multislit diffraction pattern lays perfectly on a trough of the single slit envelope
how does a monochromater work and what does it do?
it gives you a single wavelength of light from many
it works by using a diffraction grating to split the whitelight into its individual wavelengths, then, using a screen with a small hole in it, it can select the wavelength it would like.
how can we measure wavelength?
using a spectrometer. A spectrometer takes in a combination of light wavelengths, spits them using a diffraction grating, and then uses a “telescope” to rotate until light is seen- in which case the user can note the angle the light has been split to.
this can then be used to find the wavelength using the equation (peak number)(wavelength) = (slit distance)sin(measured theta)
what does polarisation mean?
an electromagnetic wave in which only one orientation of the electromagnetic wave exists.
how can we create polarised light?
AT SOURCE
em waves can be produced by elections accelerating
if we confine these electrons to one axis of movement we can produce polarised light
example: electrons moving across stretched polymer fibres
FROM UNPOLARISED LIGHT
Polaroid blocks all light passing through it apart from in one direction- think of a letterbox
by passing unpolarised light through Polaroid, it will come out at a lower intensity, but polarised
in this situation:
(intensity out) = (intensity if theta = zero)cos squared (theta)
what is the equation for mallus’ law?
(intensity out) = (intensity at theta = zero)cos squared (theta)
in words, what is Brewster’s angle?
when light hits a material such as glass, it will diffraction. This diffraction will cause a reflection to occur also. if the angle between the reflected and refracted rays are 90 degrees, it means that the reflected rays direction of energy transfer is parallel with the direction of travel in one plane. This means the reflected light is polarised. the Lange if incidence for which this occurs is the Brewster’s angle.
