2.5 Quantum Physics Flashcards
photoms
discrete energy quanta
what is energy of photon directly proportional to
frequency of EM radiation
equation linking energy of photon and frequency
E=hf
1 electronvolt
energy transferred when an atom travels through a potential difference of 1 volt
photoelectric equation
1/2mv2 = hf - hf0
what happens if the frequency is above the threshold frequency
increased intensity radiation increases rate of electron emission
photoelectric effect
EM radiation above threshold frequency shone into metal, electrons are released from surface of metal
how is photoelectric effect demonstrated
gold leaf electroscope
what happens when visible light is used on the zinc plate?
no electrons removed from plate
what happens when UV light is used on the zinc plate?
very low intensity - electrons instantaneously removed from plate
work function
minimum energy required to free an electron from the surface of the metal
threshold frequency
minimum frequency required to free electrons from surface of metal
ground state
lowest energy level for electron in atom
excited state
electrons gain energy and can move to higher energy level
ionisation state
electrons gain enough energy to completely remove from atom
how can electrons gain energy needs
absorbing photon of light
energy levels
different values, each of possible electron transitions within atom will produce photon with different energy
what would happen f the electron gained enough energy to make it all the way to 0eV?
electron free of hydrogen atom
atom missing electron
becomes hydrogen ion
use of lasers
interference experiments in labs which require coherent source of light
endoscopes for microsurgery - lasers are precision instruments
CD readers and writers - lasers retrieve data by reflecting off microscopic pits on discs
lasers acronym
light amplification by stimulated emission of radiation
what is a laser
device that controls the way that energised atoms release photons
population inversion
number of electrons in excited state more than number in ground state
how does population inversion occur?
very intense flashes of light/electric discharges pump lasing medium and create large collection of excited-state
properties of laser light
monochromatic
coherent
collimated - very tight beam and very strong & concentration
what occurs to make the 3 properties of laser light happen?
stimulated emission
production of x-rays in x-ray machine
electrode pair sit inside glass vacuum tube
cathode = heated filament
heat causes electrons to be ejected off filament surface
positive charged anode flat disc of tungsten attracts electrons across tube causing them to accelerate
electrons hit tungsten target and give off most energy - most as heat
speeding electrons collides with tungsten atom, knocks loose electron in one of atom’s lower energy levels
electrons in higher energy level immediately falls to lower energy level, releasing extra energy in form of x-ray photon
CT scanning advantages
provides real time lagging
painless, non-invasive and accurate
fast and simple
less sensitive to patient movement that MRI
performed if have implanted medical device of any kind e.g. pacemaker
CT scanning disadvantages
more expensive that conventional X-ray
x-ray dose higher than conventional x-ray
person large may not fit into opening of scanner/too heavy for table
not recommended for pregnant women
children more sensitive to ionising radiation - shouldn’t have CT scan unless necessary
How does CT scanner work?
x-ray tube mounted on movable ring around edges of hole
rings supports x-ray detectors directly opposite x-ray tube
motor moves rings so x-ray tube and detectors revolve around body
x-ray beams moves all around patient scanning from 100s of different angles
each full revolution scans narrow, horizontal ‘slice’ of body
computer takes all info and creates 3D image of body
