quantum physics

wave properties light shows?
1. reflection 2. refraction 3. diffraction 4.polarisation
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Polarized light waves are light waves in which the vibrations occur in a single plane. e.g.
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photoelectric effect
when light fell on a metal plate it released electrons instantly. increasing intensity - increased number of electrons released. decreasing the frequency - no electrons emmitted. increase intensity and give more time - no electrons emitted.
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if light were a wave ...
increasing the intensity - increase the energy of light. the energy from the light would be evenly spread across the metal and each electron would be given a small amount of energy. eventually the electron would gain enough energy to be released.
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minimum frequency of incident light which can cause photo electric emission i.e. this frequency is just able to eject electrons with out giving them additional energy. - f=o/h
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minimum energy required to emit an electron from the surface of a metal
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photosynthesis - conclusions
1.electrons were being knocked off the surface 2.reactive metals have outer electrons that can be easily removed 3.intesity is not effected IF is does not react threshold frequency 4. higher frequency = shorter wavelength
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behaviour of light?
light travels as a photon which transfer discrete packets of light
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explain the photon model of electromagnetic radiation
1. light and other electromagnetic radiation are emitted in bursts of energy - it is quantised 2.photons travel in straight lines 3.when photo released energy changes are discrete amount of quanta 4.energy lost by atom = energy of photon
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combine energy equation and wave equation
E=hf and c=fY .... E=hc/Y
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energy used when the charge of an electron moves through a p.d. of 1V - 1.6X10^-19J = 1eV
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explaining the photoelectric effect
a photo collides with an electron in the metal - tranferring energy to give the electron enough energy to be removed. some of the energy is needed to break the bonds holding the electron and the rest used as KE for it to move away. hf=o+KEmax
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y=mx+c - KE=hf-o
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hf = E1-E2
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when an electron gains the exact amount of energy to move up one or more levels
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when an electron gives out the exact amount of energy to move down to its original position
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when an electron gains enough energy to be completely removed from the atom. the levels leading up to ionisation have negative vales because they are being compared to the ionisation level - remember electrons must GAIN nergy to move up
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line spectra
each transition releases a photo with a set Y and f. we can analyse light by using a diffraction gratting to seperate the light into its different colours - called its line spectra. each element has its own line spectra
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inside a fluorescent lamp
1.it is a sealed glass tube 2.contains a small bit of mercury and a noble gas - kept at a very low pressure 3.phosphor powder coated on the inside 4.2 electrodes 1 at each end - wired to an electrical circuit 5.connected to an alternating current(AC)
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what happens when the lamp is on?
1.current flows through to the electrodes - creating a p.d. causing electrons to migrate through the gas 2.some collide with gaseous mercury atoms which excite electrons - when moving down levels photons are released
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3.electrons are arranged in mercury atoms s they release photons in the UV wavelength range 4.when a photon hits a phosphorus atom it excites an electron and the atom heats up 5.when an electron falls back it releases a photo of a new energy level
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6. this photon has less energy than before - energy was lost through heat 7.the phosphor then gives of white light - which we can see 8.manufacturers change the colour of light by using different combos of phosphors
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wave particle duality
'all particles have a wave nature' Y=h/mv Y=h/p p-momentum DE BROGLIE WAVELENGTH
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a plate of glass or metal ruled with very close parallel lines, producing a spectrum by diffraction and interference of light.
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electron diffraction
1.fired electrons at a crystal structure - which acted as a diffraction grating 3.producing areas of electrons and no electrons on the screen behind it 4.JUST LIKE the pattern when light diffracts
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electron wavelength
change in p.d =eV eV=1/2mv^2 v=_/2eV/m Y=h/mv therefore,Y=h/_/2meV
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meaning particles sometimes behave like waves and wave sometimes behave like particles
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e.g.1. light as a wave
diffraction, interference, plarisation and refraction
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e.g.2. light as a particle
photoelectric effect - light behaves as a particle called a photon
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e.g.3. electron as a particle
deflection by an electromagnetic field -- collisions with other particles
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e.g.4. electron as a wave
electron diffraction
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Card 2




Polarized light waves are light waves in which the vibrations occur in a single plane. e.g.

Card 3


photoelectric effect


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Card 4


if light were a wave ...


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