3.1 - Physics Basics

Question 1

What are radiographs created by?

Answer 1

X-ray photons that are projected through and object and then interact with the receptor on other side to form an image

Question 2

What is black in radiographs?

Answer 2

Air

Question 3

What is a lighter colour in radiographs?

Answer 3

dense enamel

Question 4

What colour is amalgam in radiographs?

Answer 4

WHite

Question 5

What colour is skin of cheek?

Answer 5

Darker image - like gingival

Question 6

What to radiographs allow us to do?

Answer 6

Aid diagnosis, planning and monitoring

Question 7

What are x-rays?

Answer 7

Type of EM radiation

Question 8

What is electromagnetic radiation?

Answer 8

Flow of energy from one point to another and is created by simultaneously varying electric and magnetic fields

Question 9

Describe properties of x-rays?

Answer 9

No mass
No charge
Travels at speed of light
Can travel in a vacuum

Question 10

What is the electromagnetic spectrum?

Answer 10

Spectrum of all the types of EM radiation and they all have different properties depending on energy wavelength and freq

Question 11

What does a shorter wavelength equal?

Answer 11

Higher frequency and higher energy

Question 12

What does a longer wavelength equal?

Answer 12

lower frequency

lower energy

Question 13

What is a wavelength

Answer 13

When top of wave moves up and down once

Question 14

What is frequency?

Answer 14

How many times the wave shape repeats per unit time and is measured in hertz

Question 15

What is freq measured in?

Answer 15

Hertz

Question 16

What does one hertz equal?

Answer 16

One cycle per second

Question 17

What is wavelength?

Answer 17

The distance over which the wave shape repeats itself and is in m

Question 18

What is speed?

Answer 18

Freq x wavelength

Question 19

What is speed of all EM radiation?

Answer 19

3x10 power 8

Question 20

What happens as wavelength decreases?

Answer 20

Freq increases

Question 21

What are photons?

Answer 21

Packets of energy that are measured in electron volts

Question 22

What are photons measured in?

Answer 22

Electron volts (eV)

Question 23

What are the types of x-rays?

Answer 23

Hard xray s

soft x-rays

Question 24

What are hard x-rays?

Answer 24

higher energy x-rays that can penetrate human tissues and are used in medical imaging

Question 25

What are soft x-rays?

Answer 25

Nit useful to medical imaging and are lower energy and easily absorbed

Question 26

What are the properties of x-rays?

Answer 26

EM radiation - no mass no charge, travels at speed of light, can travel in a vacuum man made not detectable by human sense causes ionisation

Question 27

What is ionisation?

Answer 27

Displacement of electrons from atoms/molecules

Question 28

How are x-rays produced?

Answer 28

Electrons are fired at atoms at very high speeds and on collision the kinetic energy of these electrons is is converted to electromagnetic radiation and heat - the photons are then aimed at the patient

Question 29

What are atoms made of?

Answer 29

Protons - pos mass 1 Neutrons - 0 - mass 1 Electrons - neg - mass 0

Question 30

What is the charge of nucleus?

Answer 30

Positive as composed of p and n

Question 31

What is the atomic number?

Answer 31

Number of protons

Question 32

What is mass number?

Answer 32

Number of protons and neutrons

Question 33

What charge is atom in ground state?

Answer 33

Neutral

Question 34

What do the number of electrons = when neutral?

Answer 34

No of protons

Question 35

What happens during ionisation?

Answer 35

Adding or removal of electrons to an atom (adding - neg and removing - pos)

Question 36

Where do electrons go?

Answer 36

They spin around the atom in shells - k l m n o shells

Question 37

What shell is filled first?

Answer 37

Inner shell

Question 38

Describe electron shells

Answer 38

k - 2 l - 8 m -18 n - 32

Question 39

How do we work out how many electrons a shell can have?

Answer 39

2n squared

Question 40

How are outer electrons held in shells?

Answer 40

They are held by electrostatic force

Question 41

What is electrostatic force?

Answer 41

Neg charge of electrons held in by positive charge of protons

Question 42

What is needed to remove electron from its shell?

Answer 42

Specific amount of energy to overcome attraction to positive nucleus

Question 43

What is binding energy?

Answer 43

This is the additional energy required to exceed electrostatic force

Question 44

When is electrostatic force greatest?

Answer 44

When electron is closer to nucleus

Question 45

What does the energy required to move an electron to a more outer shell away from nucleus equal?

Answer 45

The difference in binding energy of the two shells

Question 46

What happens if an electron drops to an inner shell?

Answer 46

Energy is released in form of x-ray photons if enough energy

Question 47

How much energy is required to move electron from K shell to L shell in tungsten? binding energy of k shell - 69.6 binding energy of l shell - 10.2

Answer 47

69.6-10.2 = 59.4

Question 48

What is the dental x-ray unit composed of?

Answer 48

Tube head Collimator Positioning arm Control Panel Circuitry

Question 49

What is current?

Answer 49

The flow of an electric charge usually by movement of electrons

Question 50

What units is current in?

Answer 50

Amps (A)

Question 51

What directions of current are there?

Answer 51

Direct current Alternating current

Question 52

What is DC?

Answer 52

Direct current is when current flows in one direction

Question 53

What is AC?

Answer 53

when current flow repeatedly reverses direction over and over again

Question 54

What does x-ray production require?

Answer 54

Unidirectional current - x-ray units provided by mains AC electricty so we have to use generators to modify AC so it mimics constant DC§

Question 55

What is rectification?

Answer 55

This is when AC IS MODIFIED BY GENERATOR TO MIMIC CONSTANT DC

Question 56

What is voltage?

Answer 56

Difference in electrical potential between 2 points in electrical field and is in volts

Question 57

What volatge do dental x-ray units need?

Answer 57

2 different voltages one as high as 10s of thousands of volts one as low as 10 volts

Question 58

What are transformers?

Answer 58

used to alter the voltage and current from one circuit to another

Question 59

What transformers do X-ray tubes have?

Answer 59

there are two different ones step up transformer going from mains to x-ray tube step down transformer from mains to filament

Question 60

What does a step up transformer do?

Answer 60

Increases potential difference across X-ray tube as is 60,000 to 70000 volts (60-7keV)

Question 61

What does a step down transformer do?

Answer 61

It decreases the potential difference across filament and is around 10v and 10 amps

Question 62

What is a filament?

Answer 62

The filament is the source of electrons (cathode) in x-ray tubes.

Question 63

What is x-ray beam made up of?

Answer 63

Millions of x-ray photons directed in same general direction

Question 64

What directions do photons travel in?

Answer 64

Straight line but diverge from source (not parallel)

Question 65

What happens to dose of x-rays as you increase distance from x-ray source?

Answer 65

if close to the source then full intensity beam but further away some photons pass straight by and around

Question 66

What is inverse square law?

Answer 66

if you double the distance you quarter the dose