Physics Basics

Question 1

why are radiographs useful

Answer 1

provide ability to see structures within the body
can show normal anatomy and pathology
aid diagnosis, treatment planning and monitoring

Question 2

what is electromagnetic radiation

Answer 2

flow of energy created by simultaneously varying electrical and magnetic fields

Question 3

what are the properties of EM radiation

Answer 3

no mass, no charge, always travels at speed of light, can travel in a vacuum

Question 4

what are the 7 groups in the EM spectrum

Answer 4

gamma, x-ray, UV, visible, infrared, microwave, radio

Question 5

what end of the EM spectrum has a longer wavelength and lower frequency and energy

Answer 5

radio

Question 6

what end of the EM spectrum has a shorter wavelength and higher frequency and energy

Answer 6

gamma

Question 7

what is frequency

Answer 7

how many times the waves shape repeats per unit time

Question 8

what is frequency measured in

Answer 8

hertz

Question 9

what is wavelength

Answer 9

the distance over which the waves shape repeats

Question 10

what is wavelength measured in

Answer 10

metres

Question 11

what is speed

Answer 11

frequency x wavelength

Question 12

what is the name for the packets of energy in EM radiation

Answer 12

photons

Question 13

what is energy usually measured in

Answer 13

electron volts , eV

Question 14

what is 1ev equal to?

Answer 14

energy gained by 1 electron moving across a potential difference of 1 volt

Question 15

what is the x-ray photon energy measured in volts

Answer 15

124 - 124,000 eV

Question 16

what are the types of x-rays

Answer 16

hard x-rays and soft x-rays

Question 17

what are the properties of x-rays

Answer 17

form of EM radiation, undetectable to human senses, man-made, cause ionisation

Question 18

how are x-rays produced

Answer 18

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

Question 19

what do atoms consist of

Answer 19

protons, neutrons and electrons

Question 20

what is the atomic number equal to

Answer 20

number of protons

Question 21

what is the mass number equal to

Answer 21

number of protons + neutrons

Question 22

what does the number of electrons determine

Answer 22

chemical properties of an atom

Question 23

what does it mean if an atom is in ground state

Answer 23

number of electrons = number of protons

Question 24

what is ionisation

Answer 24

removing/adding electrons to an atom

Question 25

what letter is assigned to the innermost shell around a nucleus

Answer 25

K

Question 26

what is the maximum number an electron shell can hold

Answer 26

2n (squared) (where n is the shell number)

Question 27

how are orbiting electrons held within their shells

Answer 27

electrostatic force

Question 28

what is electrostatic force

Answer 28

negative charge of electrons attracted to overall positive charge of nucleus

Question 29

what is binding energy

Answer 29

additional energy required to exceed electrostatic force

Question 30

how is electrostatic force increased

Answer 30

closer the electron is to nucleus/more positively charged the nucleus is

Question 31

what is the amount of energy required to move an electron to a more outer shell equal to

Answer 31

the difference in the binding energies of the 2 shells

Question 32

what happens if an electron drops to a more inner shell

Answer 32

the difference in binding energies between the 2 shells is released

Question 33

what is current

Answer 33

flow of electric charge usually by movement of electrons

Question 34

what is current measured in

Answer 34

amps (A)

Question 35

what is DC

Answer 35

direct current - constant unidirectional flow

Question 36

what is AC

Answer 36

alternating current, flow repeatedly reverses direction

Question 37

what is the frequency of alternating current

Answer 37

number of complete cycles (reverse and back) per unit time

Question 38

how does the x-ray machine modify the AC current to the DC current

Answer 38

rectification

Question 39

what is voltage

Answer 39

difference in electrical potential between 2 points in an electrical field

Question 40

what is voltage measured in

Answer 40

volts

Question 41

what do transformers do

Answer 41

alter the voltage and current from one circuit to another

Question 42

what are the 2 separate transformers required for x-ray unit

Answer 42

mains - x-ray tube (cathode-anode)
mains - filament

Question 43

what does a step up transformer do

Answer 43

increase potential difference across x-ray tube
60-70kV
current is milliamps

Question 44

what does a step-down transformer do

Answer 44

decrease potential difference across filament
about 10 volts
about 10 amps

Question 45

what direction do photons travel in

Answer 45

diverging straight lines

Question 46

what is x-ray beam intensity

Answer 46

quantity of photon energy passing through a cross sectional area of the beam per unit time

Question 47

what increases intensity

Answer 47

increased number and/or energy of photons

Question 48

what is intensity proportional to

Answer 48

current in filament and potential difference across x-ray tube

Question 49

what is the inverse square law

Answer 49

intensity of x-ray beam is inversely proportional to the square of the distance between x-ray source and the point of measurement

Question 50

what happens if you double the distance between source and recipient

Answer 50

quarters the dose