6+7: Waves and Quantum behaviour Flashcards
Constructive Interference
Crest+crest =big crest
Trough +trough =big trough
Superposition
When two or more waves cross the resultant displacement equals the vector sum of the individual displacements
Destructive interference
Trough+equal sized crest=Nothing
Incomplete destructive interference
Trough+ a different sized crest =not total destructive interference
Waves in phase
Both on same point in the wave cycle
Exactly out of phase
Phasers point in opposite directions, are at 180 degrees to eachother
Waves are coherent if
They have the same wavelength
And frequency and a fixed phase difference between them
Number of wavelengths to be in phase
Whole number of wavelengths difference apart only
Standing wave
The superposition of two progressive waves with the same wavelength moving in opposite directions
Standing waves are different from normal waves because
No energy is transmitted
Nodes
The amplitude of the vibration is zero
Antinodes
Points of maximum amplitude
Lowest possible resonant frequency (fundamental frequency)
One loop- half a wavelength
A node at each end
Second harmonic (first overtone)
Two loops with a node at the centre at at the ends
One wavelength
Third harmonic (second overtone)
1.5 wavelengths
Pipe closed at one end
L= 1/4 wavelength
Node at closed end
Open pipe
Antibodies form at open ends of the pipe
L= 1/2 wavelength
Speed of sound using a resonance tube
Tuning fork(labeled with a frequency) Fill tube with water and find shortest distance that the sound if fork resonates at This is 1/4 wavelength
Use v=fL
A progressive waves amplitude
All points have the same amplitude
Diffraction with a big gap
no diffraction
Diffraction with a medium gap
lines are straight with curved edges, still getting bigger
Diffraction with a small gap
completely curved lines, getting bigger
why you can hear but not see someone round a door
you can’t see someone round a door because the gap is much bigger than its wavelength
You can hear someone because the wavelength is similar to the width of the gap
the narrower the slit
the wider the diffraction pattern
the brightest point of diffraction is
the brightest point of diffraction is where light passes in a straight line from the slit to the screen as all the light that arrives there is in phase
all the other bright spots (other than the brightest)
a constant phase difference, the phasors point in slightly different directions and thus have a smaller resultant
dark fringes
phase difference add to give a resultant of zero
coherent sources
same wavelength and frequency (made with the same oscillator)
to make two coherent sources with light
one laser light (monochromatic as only one wavelength present) source and two equal slits
to find the fringe spaceing you use the equation
wavelength= xd/D
x- fringe spacing
d- spacing between slits
D- distance from slits to screen
what is a diffraction grating
youngs double slit experiment but with many slits
the angle between the incident beam and the nth order maxima is given by
sin@ = nL/d
n- nth order maxima (which line after the center one)
L-wavelength
d- distance between slits on grating
where the diffraction equation comes from
at each slit light is diffracted, each light ray interferes with each other and produce and interference pattern
the larger the wavelength
the more the pattern will spread out
if d is bigger
sin@ i smaller, the coarser the grating the less the pattern will spread out
sin@ >1
impossible
speed of light
3x10^8
photoelectric effect
free electrons on the surface of a metal absorbs lights’s energy, if it absorbs enough energy it can break free
photoelectrons are emitted if
the radiation has to be above the threshold frequency
energy carried is proportional to
the intensity of the beam
EM waves can only be released in
discrete packets called photons
Energy carried by a photon=
E=hf =hc/L
h-planck’s constant 6.63x10^-34
L- wavelength
c- speed of light 3x10^8
Planck’s constant (h)
6.63 x10^-34
the higher the frequency of a photon
the more energy it carries
work function energy
the amount of energy required to break the bonds holding an electron there
line emission spectra
light from hot gass is split with a prism or a diffraction grating
continuous spectra
if white light is split up with a prism the colors merge into each other (no gaps in the spectrum) to f
line absorption spectra
light with a continuous spectrum of energy (white light) passes through a cool gas.
Black lines will appear in the continuous spectra from where wavelengths have been absorbed by the gas
these will match up with the colored lines in a line emission spectra
to find the right energy level to what it is excited by
do n=1-given energy= energy at which it is excited
n=1 is ground state
probability of a quantum arriving
(resultant phasor)^2
how to find the frequency of rotation of a photon phasor
f= E/h
what happens the longest of the possible phasor paths
they curl up and cancel eachother out
the final phasor of the quickest past contributes the most
to the resultant amplitude and the probability of a quantum arriving at a point
when light travels in water
slows down
keeps the same frequency
energy stays the same
phasor will still have the same amplitude and frequency rotation whatever material the light is traveliing through
What is a concave mirror for
to make sure that no matter what point of the mirror the phasor hits it will have taken the same time( travelled same distance) when it reaches the focal point of the mirror
What is a convex lens for
light hiting the thin glass on the edge takes longer than the light hitting the centre. Beacause the light travels slower through the thicker glass the light emergest at the same time, they converge at a focus point
wavelength using Planck’s constant (as Quantum objects) De Broglie equation
L= h/mv
frequency using kinetic energy and Planck’s constant
f= e/h
Planck’s constant
6.63x10^-34
If you increase the electron speed
diffraction pattern circles squish together
a shorter wavelength gives
less diffraction effects
To resolve tiny detail in an image you need
a shorter wavelength
light blurs out detail more than electrons do
electron microscopes can resolve finer detail than a light microscope
How do you know electrons show quantum behaviour
accelerated electrons in a vacuum tube interact with the spaces in a graphite crystal
as an electron hits a fluorescent screen, it causes a photon to be released
you can see a diffraction pattern
electron mass
9.11 x 10^-31
power
energy/time
signals sound the same pitch
same fundamental frequency
same period of waveform
lowest frequency
number of photons per second
energy/power
why some places have bad signal
waves from two transmitters interfere destructively
the smallest separation between two places with bad signal
1/2 the wavelength
what causes a signal received to fall
the incident and reflected rays interfere destructively
the signal variation between maxima and minima
reflected wave path length changes
incident is unchanged
phase difference change4s
from out of phase to in phase
minima
lowest resultant wave (no wave formed) after superposition
number of electrons=
power / energy
units for Ke
Kgm^2 s^-2
units for Force
Kgms^-2
graph speed from rest falling / time
straight line
graph of speed falling from rest / distance
curve getting less steep
TRUE OR FALSE
More than one photon must reach the point at once if there is to be destructive interference
FALSE
Why can you use S=d/t for a package dropped from a plane for horizontal
moving horizontally with the plane
no horizontal force (Acceleration)
horizontal component not affected by gravity
How standing waves form
waves reflect at ends
travelling both directions
they superimpose (interfere) and constructively and destructively
creates Nodes and AntiNodes
Meaning of Frequency
How many vibrations in a second
units for ENERGY
J / Nm
number of photons=
total energy / energy of one photon
difference between probability proportional to
difference between light intensity
difference in amplitude^2
a graph with equation x= 1/y has shape
a negative gradient drooping inwards (almost following the axis)
Power
for speed and stuff x2
Force x velocity
mass x acceleration
Force against resistive forces
Friction
example of standing waves
wind instrument
microwaves
string instruments
why would a 0th order maxima appear yellow
made up of other colour wavelength
colours dont split up by diffraction
when cant there be a second order maxima
sin@ cant be bigger than 1
charge is (similar to energy)
Joules of energy being transferred
energy charge voltage =
v= e/Q
time period is
the time for one wavelength
