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WAVE PARTICLE DUALITY AND QUANTUM THEORY - Coggle Diagram
WAVE PARTICLE DUALITY AND QUANTUM THEORY
Waves
General
A source of energy is needed
Energy is transferred as the wave progresses
Medium itself is not moved
Mechanical Waves
Longitudinal Waves
Particles of the medium move parallel to the direction of propagation of the wave disturbance
Series of compressions and rarefactions
Compressions are when particles are closer together
Rarefactions are when particles are displaced further from their mean position
General
Needs energy source to produce a disturbance and an elastic wave
Examples include ocean waves, ripples, sound and earthquakes
Electromagnetic Waves do not require a medium
Occupy a mean position from which they can be displaced by an outside force
Restoration force makes it return to their original position
Greater the energy, the greater the displacement
Particles return to the equilibrium position after the wave has passed
Terminology
Displacement (s)
Distance from equilibrium position (m)
Amplitude
The max displacement of the medium from equilibrium
Phase
Position and motion at an instant
Particles are in phase when they have the same displacement and moving in the same direction
Period (T)
Time taken for one complete cycle (s)
Frequency (f)
Number of complete cycles per second. (Hz)
Wavelength (位)
Distance between two consecutive points in the same phase. (m)
Wave Velocity (v)
Velocity of the disturbance or wave through the medium. (v)
Side note
Compression (forward) and rarefaction (backwards) for longitudinal waves (horizontal displacement)
Crest (Max) and trough (Min) for transverse waves (vertical)
Transverse Waves
Example are Mexican waves
Particles of the medium move perpendicular to the direction of propagation of the wave disturbance
Wave Nature of Light
Diffraction
Dispersion of waves, as they pass through or around and opening
Significant diffraction occurs if aperture is about the same size as the wavelength
Reflection
Angle of incidence= Angle of reflection
Refraction
Due to a change in velocity
Frequency of the wave remains unchanged
Wavelength and direction of the wave changes
General
Huygens' Principle " Each point on the existing wave-front can be considered to act as a source for the next wavefornt."
Light was composed of longitudinal waves
Light waves slow down when they entered a denser medium, and bend towards the normal
Polarisation
Each wave of light emitted has magnetic and electric fields
You receive millions of waves per second, hence appears that the wave has E and B fields in all directions.
Can be shown with all electromagnetic waves
Plane of polarization is when materials allow light to pass only if the E fields are in a particular plane
Suggests light is a transverse wave, as longitudinal waves cannot be polarised
Superposition and interfernece
Constructive interference, is when 2 pulses combine to give a greater amplitude
Deconstructive interference is when two pulses combine to produce a pulse with a smaller amplitude
Maxwell's Electromagnetic Waves
Oscillating charges produce an oscillating B field, which then produce and oscillating E field
Light is not a mechanical wave, but consists of oscillating B & E fields at right angles.
The E/M radiation is classified in the spectrum according to the frequency with which the E and B fields oscillate
Scales on the frequency are logarithmic
Low energy radiation (radio waves) are more wave like while high energy (gamma rays) are more particle like.
High energy waves are ionizing
Visible light between 700 (red)-400 (violet) nm
If a charged particle oscillates it produces an electromagnetic wave
The EM wave it produces has the same frequency when it is oscillating
E field is strongest and most intense in directions perpendicular to the antenna and zero along the axis of the antenna.
Formulas
V= f位
C= f位
E= hf
E= hc/位
饾湵= hf
EK= hf-饾湵
F= Eq
KE (max)= Vq (stopping voltage)
位=h/p
E(photon)= E2-E1=hf=hc/位
En = -13.6eV/n^2
Photons and Quanta
Blackbody Radiation
A black body is an ideal absorber and emitter
Atoms could only absorb or emit radiation in specific, non-continuous amounts, known as quanta
Photoelectric Effect
Electromagnetic radiation knocks electrons off the surface of a metal plate (current generated), this is known as the photoelectric effect
Current of photoelectrons called the photocurrent
Rheostat measures voltages
Below a certain frequency no electrons are emitted
KE of emitted electrons depends on frequency of light, not intensity
Intensity affects number of electrons ejected ( more intense, more ejected, more current detected)
No time delay between light hitting the metal surface and electrons ejected
Photon
Light is not a continuous wave, but existed as a stream of quanta, now called a photon
Photons are little packets of light with wave-like properties, unlike particles have no mass
Explaining the Photoelectric effect
Light has momentum, a characteristic of particles
Brighter light means more photons, and each photon will eject one electron
Each photon must have energy equal to or more than the work function of the material or will not eject electrons
Electron released by a photon having 饾湵 will have 0 KE
If E of photon is >饾湵, this extra energy will appear as KE
To measure the KE of ejected photoelectrons, the target metal becomes the +ve cathode, so the photoelectrons move towards the anode
This causes electric fields to accelerate the photoelectrons backwards
When the current stops it is called the stopping voltage.
Examples include alarms, automatic lights, light meters, radiation detectors, anywhere EMR turned into a current
Wave- Particle Duality
Interactions between light and matter can be viewed as energy transfer between two particles colliding.
Energy and momentum are explained by viewing light as a wave, even though these are particle properties
Moving particles exhibit wave properties
Atoms, Energy Levels and Spectra
Bohr Model
Energies of orbital electrons is quantized, hence they can exist in discreet energy levels
1 is the lowest energy or ground state, closest to the nucleus
Energy increases as you move away from the nucleus
At normal temp, electrons will exist in the lowest energy state, any higher energy state us called an excited state
Radiation is emitted as an electron moves from a higher to lower energy state.
The -ve energy is negative because it is necessary to add energy to the electron to free it from the atom
Energy levels are discrete
A spectrum is simply all the frequencies of light coming from a material, they are classified as emission or absorption
Emmision Spectra
Line Emission Spectra
Produced by gases under low or normal pressures
Each element has its own characteristic line spectrum
Band emission
Band emission
Due to excitement of molecules rather than atoms
Sharp edge and a diffuse edge
Made up of a group of lines which come closer together as they approach the sharp edge.
Produced by flames, as they have a thin layer of CO and water which account for the bands in emission spectra
General
Obtained by the dispersion of light coming directly from the source
Continuous emission
Produced by light from hot incandescent solids
Consists of all colours
Absorption Spectra
General
Produced by the dispersion of light that has passed through some absorbing material
Black is the absence of light
Line absorption
White light passed through vapour, photons f the frequencies corresponding to the line emission spectrum of that gas will now be absorbed
Lines are dark, not black
The solar spectrum
lines are called Fraunhofer lines
Due to selective absorption of certain frequencies of white light
Band absorption
Like line absorption but when light white passes through a solid or liquid
How Bohr model explains Spectra
General
Amount of energy absorbed by the electron is equal to the difference between energy levels
When electrons move back to lower energy levels they give off EM radiation
if electron is ejected, atom is ionized
Paschen series (infrared)
Balmar series (visible region)
Lyman series (UV)
Collisional Excitation
Thermal excitation
When collide, transfer energy
Added energy can raise an electron to a higher energy level
In hot materials more collisions with higher energy and more frequent
Hot materials emit more radiation due to thermal excitation
Electron excitation
Atom may take any convenient slice of an electrons energy
Leftover energy is KE of the bombarding electron
Always possibility to miss (elastically) or hit (inelastically)
Radiative excitation
Atom must take all the photon energy or none of it
Hit or miss again a possibility
An excited atom cannot be further excited, as they almost immediately return to ground state, not in the excited state long enough to absorb energy
Can excite multiple atoms
Ionized when a electron is liberated from a neutral atom
Bombarding electrons will only lose an amount of energy equal to one of the energy levels