Basic Physics

Question 1

X-rays are a form of what kind of radiation?

Answer 1

Electromagnetic radiation

Question 2

The flow of energy from electromagnetic radiation is created by what? What is it represented by?

Answer 2

Simultaneously varying electrical and magnetic fields Represented as a sine wave

Question 3

What are the properties of electromagnetic radiation? (4)

Answer 3

• no mass
• no charge
• Always travels at the ‘speed of light’ (3x10⁸ ms^-1 = 671 million mph)
• Can travel in a vaccum

Question 4

Describe the EM spectrum (3 main points).

Answer 4

• consists of all the diff types of EM radiation
• Each type has diff properties depening on its energy/wavelength/frequency
• 7 main groups

Question 5

What are the 7 EM groups?

Answer 5

• gamma ray
• X-ray
• Ultraviolet
• Visible light
• Infrared
• Microwave
• Radio

Question 6

Describe gamma rays in terms of wavelength, frequency and energy.

Answer 6

Shorter wavelength, higher frequency and higher energy

Question 7

What is the wavelength?

Answer 7

How ‘big’ one cycle is

Question 8

What is the frequency of a wave? What is it measured in?

Answer 8

How many times the wave’s shape repeats per unit time

Hertz (Hz) [one hertz = one cycle per sec]

Question 9

Speed = frequecny x wavelength

BUT EM radiation speed is constant (3x10⁸ms^-1)

What does this mean for the relationship between frequency and wavelength in EM radiation?

Answer 9

If frequency increases then wavelength must decrease (and vis versa)

Question 10

photons and mocement of enery etc

Question 11

What are the 2 types of X-rays you get?

Answer 11

• Hard x-rays
• Soft x-rays

Question 12

Describe hard x-rays.

Answer 12

Higher energies and are able to penetrate human tissues

(mediacal imaging mainly uses these types of x-rays)

Question 13

Descibe soft X-rays.

Answer 13

Lower energies and easily absorbed

NOTE: dont want soft x-rays if want radiographs as you need some x-rays to reach the receptors

Question 14

What are the basic properties of X-rays? (4)

Answer 14

• form of EM radiation (no mass, no charge, very fast, can travel in a vaccum)
• undetectable to human senses (contrasts with visible light)
• Man-made
• Cause ionisation (displacement of electrons from atoms/molecules)

Question 15

How are x-rays and gamma rays similar?

Answer 15

They are identical except that gamma rays ocur naturally and X-rays are man-made

Gamma rays also generally have higher energies

Question 16

Describe the basic production of X-rays.

Answer 16

• Electrons fired at atoms at very high speed
• On collision, the kinetic energy of these electrons is converted to electromagnetic radiation (ideally X-rays) and heat is produced as a side-effect
• The X-ray phoons are aimed at a subject

Question 17

What is the basic structure of an atom?

Answer 17

Question 18

Describe neutrons, protons and electrons. (charge, mass, location)

Answer 18

Question 19

What is the overall charge of the nucleus?

Answer 19

Positive

Question 20

What dictates the atomic number and mass number of an element?

Answer 20

AN = number of protons

Mass number = protons + neutrons

Question 21

The number of electrons determines what in an atom?

Answer 21

Its chemical properties

Question 22

What is the innermost electron shell?

Answer 22

K (then it foes L, M, N, O etc.)

Question 23

How do you figure out the max no. of electrons a shell can hold?

Answer 23

max. no. = 2n² (n=shell number)
e. g. L shell = 2x2² = 8 electrons

Max no.’s for first shell’s go (2, 8, 18, 32)

Question 24

Orbiting electrons are held within their shells by what?

Answer 24

Electrostatic force

(-ve charge of electrons attracted to overall +ve charge of nucleus)

Question 25

To remove an electron from its shell, a specific amount of energy is required to overcome the electrostatic force. What is this energy called?

Answer 25

Binding energy (additional energy required to exceed electrostatic force)

Question 26

The energy required to move anelectron to a more outer shell requires what energy?

Answer 26

The difference between the 2 binding energies of the shells

Question 27

If an electron drops to a more inner shell, what energy is required?

Answer 27

none - the difference in the 2 binding energies is released Can be released in the form of heat or x-rays (if sufficient energy)

Question 28

What are the main components of a dental X-ray unit?

Answer 28

Tubehead Collimator Positioning arm Control panel Circuitry

Question 29

What is the definiion of a current?

Answer 29

Flow of electric charge, usually by the movement of electrons

Question 30

What are currents measured in? Describe this measurement.

Answer 30

Amps Measure of how much charge flows past a point per second

Question 31

Currents can also be defined by their direction. What are these 2 categories? Describe them.

Answer 31

Direct current (DC) = constant unidirectional flow e.g. batteries Alternating current (AC) = flow repeatedly reverses direction

Question 32

When it comes to powering machienary, does it matter what direction a current is flowing in?

Answer 32

No - as long as it is flowing

Question 33

Answer 33

Question 34

X-ray production requires what kind of current? (direction)

Answer 34

Unidirectional current

Question 35

X-ray production requires a unidirectional current BUT x-ray units are powered by mains electricity (AC - alternating currents). How is this problem resolved? What is the process called?

Answer 35

X-ray units have generators which modify the alternatig current so that it mimics a constant directional current Process called rectification

Question 36

What is the voltage?

Answer 36

Difference in electrical potential beween 2 points in a n electrical fiels Related to how forcefully a charge will be pushed through an electrical field NOTE: potential differenece is the same as voltage and the unit for voltage is volt

Question 37

Describe the electrical supply to an X-ray unit in the UK mentioning the current and volts.

Answer 37

From mains supply: - alternating current (less than or equal to 13 amps) [need DC but fixed by rectification) - 220-240 volts

Question 38

What voltages does an X-ray machiene need?

Answer 38

2 diff voltages: - one as high as 10s of thousands of volts - one as low as around 10 volts (mains supply only gives a voltage of 220-240 volts)

Question 39

How is the problem of volatge (mains supply not sufficient) for the X-ray machines resolved?

Answer 39

Transformers alter the voltage (and current) from one circuit to another

Question 40

What transformers are found in the X-ray unit?

Answer 40

2 diff ones: - Step-up transformer for the X-ray tube - Step-down transformer for the filament

Question 41

Describe the step-up transformer.

Answer 41

increases potential difference across x-ray tube Usually 60,000-70,000 volts (60-70kV) Current reduced to milliamps (mA)

Question 42

Describe the step-down transformer.

Answer 42

decrease potential difference across filament approx 10 volts approc 10 amps

Question 43

What are x-ray beams made up of?

Answer 43

Millions of x-ray photons directed in the same general direction

Question 44

Describe how the photons in X-ray beams move/travel?

Answer 44

Effectively travel in straight lines but **diverge** from the X-ray source (dont travel in parallel)

Question 45

What is the x-ray beam inensity defined as? READ PIC AND UNDERSTAND

Answer 45

The quantitiy of photon energy passing through a cross-sectional area of the beam per unit time Increase in number and/or energy of phtons = increase in intensity

Question 46

The dose from the X-ray decreases with what?

Answer 46

Distance from the x-ray

Question 47

What is the inverse square law that describes intensity of x-ray beam at a point?

Answer 47

Question 48

Answer 48

answer = 0.25 grays

Question 49

What is the difference between other types of ionising radiation and x-rays?

Answer 49

others produced by radioactive decay of unstable atoms unlike x-rays which are directly man-made