MODULE 4: WAVES AND QUANTUM Flashcards
What is a progressive wave
Oscillation through space that transfers energy
Types of waves
Transverse
Longitudinal
Transverse vs longitudinal
Oscillation is perpendicular to energy transfer in transverse, parallel in longitudinal
Examples mechanical waves
Sound water etc
Examples transverse
EM, surface water ripples
What is the wave equation
v = lambda * f
Types of wave graphics and axis
Displacement distance (y,x) Displacement time (y, x)
What is phase difference
Difference between how far in a single oscillation two waves are at a point in time, in radians
How to find distance between two points on wave of phase different x
(x/2pi) * wavelength or (x/360) etc for degrees
What is reflection
When a wave bounces off a surface, staying in the same medium.
Angle of incidence is always the angle of reflection
What is refraction
When a wave changes medium, eg air to water
or deep to shallow water in terms of surface ripples
What is constant in refraction and what changed
Frequency is const
So speed and wavelength change
What is diffraction
Spreading of a wave when is goes through a aperture (gap)
When is diffraction significant and when not
When aperture size is close to wavelength
When it’s much much smaller very little happens
What is wave polarisation
When a waves oscillations move to only one plane, making it plane polarised
What parts make up the EM wave
Magnetic field , and electric field both in different planes with phase different of 90 deg
What is polarisation filter
A piece of ‘paper’ which when two are oriented correctly block all light, because it’s all plane polarised
Which em wave has lowest wavelength, and which has highest wavelength
Radio have highest
Gamma have lowest
Name em spectrum
Radio micro infrared visible ultraviolet (X-ray gamma)
What is intensity of a progressive wave
Radiant power passing at right angle per unit surface area (it hitting the area)
Intensity equation and unite
I=P/A Wm^-2
What two things is intensity proportional to
1/r^2 of a surface area
amplitude^2 of a wave
4 properties of EM waves
transverse
Travel in vacuum
Speed of 3*10^8ms^-1
Have two components electric and magnetic fields
What are polarisation filters called
Polaroid paper
How to test polarisation with microwaves/visible light waves
EQUIP: microwave transmitter and receiver, metal grille (or two pieces of polariod paper if it’d visible light)
EXPERIMENT: rotate the grille or paper to see how the receiver doesn’t receive as much anymore
What is refraction index
Ratio of light speed to the speed of the light in the medium.
Not between 0 and 1
n=c/v
Refractive index of air
1.0003
What is the refraction law
n1 sin theta 1 = n2 sin theta 2
What is total internal reflection and what are the two properties
When the light wave reflects back into the same medium
- destination material has lower refractive index
- Angle of incidence I > critical angle
What happens when angle of incidence is equal to the critical angle
Light refracts along the boundary the media
What two things happen when the angle of incidence is less than the critical angle
Refraction Partial reflection (the light REFLECTS but not as intense)
What is the critical angle
minimum angle which rays of light passing through a denser to less dense medium are able to be totally reflected. (TIR)
When can you use critical angle and what is the equation
when light going from material to air
sin critical angle.(C) = 1/n
N = refractive index
Where does critical angle equation come from
If angle of incidence is equal to critical angle light travels along the boundary, so theta 2 is 90 because it’s 90 from the normal. Sin90 = 1 so n1sin1 = 1, because it’s material to air and air refractive index is 1
So sinC = 1/n
Refractive index can be throughout of as
How much slower the speed of light in the medium is compared to air (where n is 1)
What is a photon
Packet of energy, a quantum of electromagnetic energy
How the energy of a photon related to the frequency of the wave
E=hf, Planck constant
What is the electron volt
A unit of energy for dealing with small amounts of energy
Electron volt symbol and unit
eV = charge * voltage, voltage = energy / charge, so eV v energy in joules
What happens when a LED looses energy
Emits photons
What is the photoelectric effect
When electromagnetic radiation is used to remove electrons from the surface of metals
How to test to find planks const
have multiple coloured LEDs adjust voltage until light just appears to come through
Record V and the wavelength of the LED
eV = approx hf = hc/lambda
Plot threshold V against 1/lambda, so the gradient is hc/e. C and e are known constants, so you can find out planks constant from that
What is used to test photoelectric effect
Gold leaf electroscope
With negative zinc plate shining electrons onto it from laser etc, gold leaf will move up
What is the work function and threshold frequency
Work function is minimum energy of a metal to free an electron from its surface
Threshold frequency is the minimum frequency of the incoming wave to free electrons from the surface
Work function formula
hf (energy) = Ek(max) + Φ
What is Einstein’s equation
The work function equation hf = ekmax + Φ
Two quantum rules
Photon can interact with only one electron at a time
Energy is conserved in photon electron interaction
What is a work function for a given element
Energy needed to free an electron from an electron shell
What graph is used to determine h as the gradient
ekmax = hf - Φ
y = Mx + c
c = -Φ, so Φ is -c
m is h is frequency and ekmax are plotted
What is wave particle duality
Electromagnetic waves have a dual nature, they travel as waves but act like photons
Act according to wave and photon model
What is de Broglies equation and what does it mean
wavelength = h / p, where p is momentum so lambda = h/mv
a particle travelling through space with momentum p has an associated wavelength
How to test de broglie equation
Electron diffraction tube:
Accelerated electrons pass through sheet of graphite
The atomic structure of graphite is layered sheets of electrons, the separation is similar to the de Broglie wavelength of the electrons causing them to diffract
The diffracted electrons create rings on the screen in front of the graphite sheet, showing the diffracted electrons
What is superposition
When to waves meet and combine
Principle of superposition
When waves meet, resultant displacement is the sum of displacements of the waves
What is coherent waves
Constant phase difference and frequency, therefore wavelength and speed and same type
What is interference
Superposition of waves from two coherent sources
What is path difference
Distance (multiples of wavelengths) between two coherent wave sources
What is constructive interference
When the waves have a phase difference of 0 or 2pi
The resultant wave is double the amplitude
What is destructive interference
When waves phase difference is pi, 180. Waves displacements cancel out
Resultant wave is practically no amplitude
What path differences given constructive and destructive waves
Constructive have any integer multiply of lambda eg 1lambda, 10lambda
Destructive have any integer and a half wave, eg 1.5, 2.5, 0.5, n/2 lambda
What is Young’s double slit
Experiment which uses two narrow slits to determine the wavelength of monochromatic light
What is monochromatic light
Light with only one wavelength, not a combination light white light
Young double slit formula
Wavelength = ax/D X = fringe sep a = slit sep D = screen to slit sep
Describe experiment to determine young double slit wavelength of laser
EQUIP: laser, paper with two small slits, piece of cardboard
EXPERIMENT: shine the laser at the slits so they diffract, and observe the diffraction pattern on the cardboard which is placed distance D away, measure the slit separation a.
Measure some amount of red dots per side of the middle central maximum.
Count the dots and take one away from that to measure the empty spaces. Divide the measurement by this number to get the fringe separation
Calculate wavelength
What is a stationary wave
When two progressive waves superpose when travelling in opposite directions.
What does a stationary wave move like
It doesn’t move only it’s amplitude appears to move, it’s amplitude moves getting bigger and smaller but it appears to not move, it’s distance looks always 0
https://en.wikipedia.org/wiki/Standing_wave
See animation
What is an anti node and a node
Node is point with no amplitude
Antinode has maximum amplitude
Differences between progressive and stationary waves
Progressive waves transfer energy
Phase difference in stationary waves is between 0 and pi only
Average wavelength of radio micro andinfrared
1000,10^-2,10^-5
Average wavelength of visible light
10^-6
Average wavelength of UV
10^-8
Average wavelength of X-ray and gamma
X-ray 10^-10
Gamma 10^-12
How can the time constant be measured for a capacitor circuit (3)
Connect voltmeter across resistor in parallel with capacitor (1) use a stopwatch to record when it gets to 37 percent of its initial value (e to the minus 1) (1) this is the time constant , time to reach 37 percent of its initial value
