Physics Basics

Question 1

what are radiographs?

Answer 1

images created by X-rays which have been projected through an object & then interacted with a receptor

Question 2

what are X-rays?

Answer 2

a form of electromagnetic radiation

Question 3

what is electromagnetic radiation?

Answer 3

the flow of energy (from one point to another) created by simultaneously varying electrical & magnetic fields
- represented as a sine wave

Question 4

what are the properties of electromagnetic radiation?

Answer 4

• no mass
• no charge
• travel at speed of light
• can travel in a vacuum

Question 5

what is the speed of light?

Answer 5

3x10^8 ms-1

Question 6

different electromagnetic wave type has different properties, what is this based on?

Answer 6

Dependent on the waves;
- energy
- wavelength
- frequency

Question 7

what are the 7 groups on the EM spectrum? (from higher energy to lowest enegry)

Answer 7

• gamma ray
• X-ray
• ultraviolet
• visible
• infrared
• microwave
• radio

Question 8

what is the definition of the frequency of a wave?

Answer 8

refers to how many times the waves shape repeats per unit time
(one hertz = one cycle per second)

Question 9

what is wave frequency measured in?

Answer 9

hertz
- Hz

Question 10

what is the definition of the wavelength of a wave?

Answer 10

the distance over which the wave’s shape repeats

Question 11

what is wavelength measured in?

Answer 11

meters
- m

Question 12

how is the speed of a wave calculated? how is this important in EM spectrum waves?

Answer 12

Speed = Frequency x Wavelength

Speed of all EM radiation is constant (speed of light)
- therefore if frequency of a wave increases then wavelength must decrease (vice versa)

Question 13

the energy of a wave is directly related to what?

Answer 13

energy is directly proportional to frequency
- high frequency = high energy

Question 14

what is energy measured in?

Answer 14

electron volts
- eV

Question 15

what does 1 eV mean?

Answer 15

energy (in joules) gained by 1 electron moving across a potential difference of 1 volt

Question 16

what physicist discovered X-rays?

Answer 16

Wilhelm Röntgen

Question 17

what are the different types of X-rays? which are commonly used in medical settings?

Answer 17

1. Hard X-rays (higher energies, able to penetrate human tissues)
2. Soft X-rays (lower energies, easily absorbed)

Hard X-rays commonly used in medical settings

Question 18

what can X-ray photon energies range from?

Answer 18

123eV - 124keV

Question 19

what are the properties of X-rays?

Answer 19

• EM radiation properties
• undetectable to human senses
• man made
• cause ionisation

Question 20

what is ionisation?

Answer 20

displacement of electrons from atoms/molecules

Question 21

how are X-rays produced?

Answer 21

• electrons fired at atoms at a very high speed
• on collision, kinetic energy of these electrons is converted to EM radiation (X-rays) & heat
• the X-ray photons are aimed at a subject

Question 22

what are atoms? what do they consist of?

Answer 22

The ‘building blocks’ of matter
- protons
- neutrons
- electrons

Question 23

what is the charge of a neutron?

Answer 23

0

Question 24

what is the charge of a proton?

Answer 24

+1

Question 25

what is the charge of a electron?

Answer 25

-1

Question 26

what is the relative mass of a neutron?

Answer 26

1

Question 27

what is the relative mass of a proton?

Answer 27

1

Question 28

what is the relative mass of an electron?

Answer 28

0

Question 29

what is the overall charge of a nucleus?

Answer 29

positive charge

Question 30

what is the atomic number?

Answer 30

number of protons in the nucleus

Question 31

what is the mass number?

Answer 31

number of protons & neutrons in the nucleus

Question 32

what does the number of electrons determine in an atom?

Answer 32

the chemical properties of the atom

Question 33

if an atom is in its ground state, what does this mean?

Answer 33

number of electrons = number of protons the atom is neutral

Question 34

If an electron is added to an atom, what does that atom become?

Answer 34

a negative ion

Question 35

If an electron is removed from an atom, what does that atom become?

Answer 35

Positivé ion

Question 36

where are electrons found in relation to the atom?

Answer 36

they spin around the nucleus in orbits/shells - cannot exist between these shells

Question 37

How are electron shells labelled & filled?

Answer 37

Innermost shell is K - then L, M, N, O etc. Fill available spaces in inner shells first

Question 38

What is the maximum number of electrons the K shell can hold?

Answer 38

2

Question 39

What is the maximum number of electrons the L shell can hold?

Answer 39

8

Question 40

What is the maximum number of electrons the M shell can hold?

Answer 40

18

Question 41

How do you work out the maximum number of electrons a shell can hold?

Answer 41

2n^2 (where ‘n’ is the shell number)

Question 42

How are orbiting electrons held within shells? How can this be altered?

Answer 42

electrostatic forces - to remove an electron from its shell, a specific amount of energy is required to overcome this attraction

Question 43

what is binding energy?

Answer 43

additional energy required to exceed electrostatic force - the closer the electron is to the nucleus, the greater the electrostatic force

Question 44

what is current?

Answer 44

flow of electric charge, usually by the movement of electrons - measured in amp/amperes A

Question 45

what does DC and AC stand for?

Answer 45

DC = direct current (constant unidirectional flow) AC = alternating current (flow repeatedly reverses direction)

Question 46

Why is it a problem that X-ray machines are powered by mains electricity?

Answer 46

because X-ray production requires a unidirectional current - therefore X-ray units have generators which modify the AC so that it mimics DC