Physic Basics Flashcards
what are radiographs
images produced by x-rays passing through an object and interacting with a receptor
what do the different shades of grey on a radiograph correspond to
how dense the tissue it has passed through is
what are the common intraoral radiographs
periapical
bitewing
occlusal
what are the common extraoral radiographs
panoramic
lateral cephalograms
what are x-rays a form of
electromagnetic radiation
what is electromagnetic radiation
flow of energy created by simultaneously varying electrical and magnetic fields
what are the properties of electromagnetic radiation
no mass
no charge
always travels at speed of light
can travel in vacuum
how do you calculate wave length
the length of the cycle divided by how many sine waves there are
how do you calculate frequency
cycles divided by the amount of time its taken
what is frequency and how is it measured
how many times the waves shape repeats per unit time and measured in hertz
what is wavelength and how is it measured
the distance over which the wave’s shape repeats measured in metres
what is the calculation of speed
speed = frequency x wavelength
how does energy move in electromagnetic radiation
via photons
what are the types of x-ray
hard and soft
what are hard x-rays
able to penetrate through human tissues
what are soft x-rays
easily absorbed
what separates x-rays from gamma rays
x-rays are man made
what is ionisation
displacement of electrons from atoms
how are x-rays produced
electrons are fired at atoms at very high speeds and when they collide the kinetic energy of the electrons is converted to electromagnetic radiation and heat - the x-ray photons released are aimed at the subject
what do atoms consist of
protons
neutrons
electrons
what is the relative charge, mass and location of a neutron
charge - 0
mass - 1
nucleus
what is the relative charge, mass and location of a proton
charge - +1
mass - 1
nucleus
what is the relative charge,, mass and location of an electron
charge - -1
mass - 0
shells
what does the atomic number relate to
number of protons
what does the mass number relate to
the number of protons and neutrons
what is the most inner shell in an atom called
K - then proceeds through the alphabet from K
how do you calculate the maximum number of electrons a shell can hold
2 x the shell number squared
how are electrons held within their shell
electrostatic force
what is the binding energy
the energy required to exceed electrostatic force (eg remove an electron from its shell)
where is the electrostatic force greatest
the shells closest to the nucleus
when there is a higher atomic number (aka more protons)
how does an electron move to a more outer shell
energy that equals the difference in the binding energies of the two shells
how does an electron move to an inner shell
energy is released
what two values do you need to be able to calculate the energy needed to move an electron
binding energy of atom A
binding energy of atom B
what are the x-ray equipments for dental x-ray units made up of
tubehead
collimator
positioning arm
control panel
circuitry
what is current
the flow of electric charge usually by movement of electrons - measured in amps
what are the two forms of current direction
direct current - constant unidirectional flow
alternating current - flow repeatedly reverses direction
what is an alternating current cycle
the reverse and reverse back time (eg mains electricity)
what does x-ray require the current to do
be flowing in one direction
since x-rays are powered by mains electricity which is AC but x-rays require DC how does this come about
X-ray units have generators that modify the AC so it mimics a constant DC
what is rectification
X-ray units have generators that modify the AC so it mimics a constant DC
what is voltage
difference between negatively charged points in one place and positive in another
aka potential difference
what voltages does x-ray units require
high as 10s of thousands of volts
one as low as 10 volts
how do we get two difference voltage values from mains (240) voltage
through the use of transformers
what are transformers
alter the voltage and current from one circuit to another
how many transformers are required for an x-ray unit
mains - x-ray tube (cathod-anode)
mains - filament
what two transformers are there
step-up transformer which increases the voltage
step down transformer which dcreases the voltage
what is x-ray beam made up of
millions of photons directed in a same general direction
what is x-ray beam made up of
millions of photons directed in a same general direction
but they diverge away from x-ray source and do not travel parallel
what is the x-ray beam intensity
quantity of photon energy passing through a cross-sectional area of the beam per unit time
how can you increase intensity of an x-ray
increasing number or energy of photons
how does divergence of x-ray beam affect the dose given
the further away, dose decreases
what is the inverse square law
the intensity of the x-ray beam is inversely proportional to the square of the distance between the x-ray source and the point of measurement (doubling distance = quarter dose)
