Physics Basics Flashcards
why are radiographs useful
provide ability to see structures within the body
can show normal anatomy and pathology
aid diagnosis, treatment planning and monitoring
what is electromagnetic radiation
flow of energy created by simultaneously varying electrical and magnetic fields
what are the properties of EM radiation
no mass, no charge, always travels at speed of light, can travel in a vacuum
what are the 7 groups in the EM spectrum
gamma, x-ray, UV, visible, infrared, microwave, radio
what end of the EM spectrum has a longer wavelength and lower frequency and energy
radio
what end of the EM spectrum has a shorter wavelength and higher frequency and energy
gamma
what is frequency
how many times the waves shape repeats per unit time
what is frequency measured in
hertz
what is wavelength
the distance over which the waves shape repeats
what is wavelength measured in
metres
what is speed
frequency x wavelength
what is the name for the packets of energy in EM radiation
photons
what is energy usually measured in
electron volts , eV
what is 1ev equal to?
energy gained by 1 electron moving across a potential difference of 1 volt
what is the x-ray photon energy measured in volts
124 - 124,000 eV
what are the types of x-rays
hard x-rays and soft x-rays
what are the properties of x-rays
form of EM radiation, undetectable to human senses, man-made, cause ionisation
how are x-rays produced
electrons are fired at atoms at a very high speed
on collision the kinetic energy of the electrons is converted to EM radiation
x-ray photons aimed at a subject
what do atoms consist of
protons, neutrons and electrons
what is the atomic number equal to
number of protons
what is the mass number equal to
number of protons + neutrons
what does the number of electrons determine
chemical properties of an atom
what does it mean if an atom is in ground state
number of electrons = number of protons
what is ionisation
removing/adding electrons to an atom
what letter is assigned to the innermost shell around a nucleus
K
what is the maximum number an electron shell can hold
2n (squared) (where n is the shell number)
how are orbiting electrons held within their shells
electrostatic force
what is electrostatic force
negative charge of electrons attracted to overall positive charge of nucleus
what is binding energy
additional energy required to exceed electrostatic force
how is electrostatic force increased
closer the electron is to nucleus/more positively charged the nucleus is
what is the amount of energy required to move an electron to a more outer shell equal to
the difference in the binding energies of the 2 shells
what happens if an electron drops to a more inner shell
the difference in binding energies between the 2 shells is released
what is current
flow of electric charge usually by movement of electrons
what is current measured in
amps (A)
what is DC
direct current - constant unidirectional flow
what is AC
alternating current, flow repeatedly reverses direction
what is the frequency of alternating current
number of complete cycles (reverse and back) per unit time
how does the x-ray machine modify the AC current to the DC current
rectification
what is voltage
difference in electrical potential between 2 points in an electrical field
what is voltage measured in
volts
what do transformers do
alter the voltage and current from one circuit to another
what are the 2 separate transformers required for x-ray unit
mains - x-ray tube (cathode-anode)
mains - filament
what does a step up transformer do
increase potential difference across x-ray tube
60-70kV
current is milliamps
what does a step-down transformer do
decrease potential difference across filament
about 10 volts
about 10 amps
what direction do photons travel in
diverging straight lines
what is x-ray beam intensity
quantity of photon energy passing through a cross sectional area of the beam per unit time
what increases intensity
increased number and/or energy of photons
what is intensity proportional to
current in filament and potential difference across x-ray tube
what is the inverse square law
intensity of x-ray beam is inversely proportional to the square of the distance between x-ray source and the point of measurement
what happens if you double the distance between source and recipient
quarters the dose
