Physics Basics

Question 1

What are the 7 properties of X-rays ?

Answer 1

Undetectable to human senses.
Man made.
Cause ionisation - displacement of electrons from atoms.
No mass.
No charge.
Travel at speed of light - 3x108 ms-1.
Can travel in vacuum.

Question 2

What will a X-rays wavelength, frequency and energy look like in comparison to other electromagnetic radiations ?

Answer 2

High frequency.
Short wavelength.
High energy.

Question 3

Define frequency.

Answer 3

How many times wave shape repeats itself in one unit time.

Question 4

What is frequency measured in ?

Answer 4

Hz
i.e. 1 cycle in one second = 1Hz.

Question 5

Define wavelength.

Answer 5

Distance over which wave shape repeats itself.

Question 6

What is wavelength measured in ?

Answer 6

Metres.

Question 7

How can speed be calculated from wavelength and frequency ?

Answer 7

Speed = wavelength x frequency.

Question 8

What speed do x-rays travel at ?

Answer 8

Speed of light - 3x108ms-1.

Question 9

What are photons ?

Answer 9

Smallest possible packets of EM energy.

Question 10

What do X-ray photon energies range between ?

Answer 10

124eV to 124keV.

Question 11

What type of x-rays are used in dentistry and medicine ?

Answer 11

Hard x-rays.

Question 12

What is the difference between hard and soft x-rays ?

Answer 12

Hard have higher energies.

Question 13

What is the minimum energy of hard x-ray ?

Answer 13

> 5keV.

Question 14

Describe how x-rays are produced.

Answer 14

1. Electrons fired at atoms at high speed.
2. On collision, kinetic energy of electrons is converted to electromagnetic x-rays and heat.
3. X-ray photons are then aimed at subject.

Question 15

What is the atomic number of tungsten atom ?

Answer 15

74 i.e. no. of protons.

Question 16

What is the mass of tungsten atom ?

Answer 16

184 i.e. no. of protons and neutrons as their mass = 1.

Question 17

Describe an atom in ‘ground state’.

Answer 17

Number of electrons = number of protons so neutral charge.

Question 18

Describe ionisation.

Answer 18

Loss or addition of electron to atom.

Question 19

Define binding energy.

Answer 19

Additional energy required to exceed electrostatic force i.e. remove electron.

Question 20

What are the 5 components of an X-ray tube ?

Answer 20

Tubehead.
Collimator.
Positioning arm.
Circulatory.
Control panel.

Question 21

Define current.

Answer 21

Flow of electric charge by movement of electrons.

Question 22

What is current measured in ?

Answer 22

Amps i.e. how much charge flows by point in one second.

Question 23

Describe direct current (DC).

Answer 23

Unidirectional flow of charge.

Question 24

Describe alternating current (AC).

Answer 24

Constant reversal of direction of charge.

Question 25

What are Hz ?

Answer 25

Cycles of reversal of direct of charge in AC per second.

Question 26

What is mains AC Hz in UK ?

Answer 26

50Hz.

Question 27

What is the process of changing mains AC to DC for purpose of x-ray called ?

Answer 27

Rectification.

Question 28

What voltages do x-rays requires ?

Answer 28

2x types of voltage. 10kV and 10V.

Question 29

Where in the xray machines are transformers required ?

Answer 29

Mains to X-ray tube. Mains to filament.

Question 30

What is a step up transformer used for ?

Answer 30

Increasing potential difference across X-ray tube to 60kV-70kV. Reduce current to mA.

Question 31

What is a step down transformer used for ?

Answer 31

Decreasing potential difference across filament to 10V. 10A.

Question 32

Describe the pathway a xray beam takes ?

Answer 32

Travels in straight line but diverges from x-ray source.

Question 33

Define x-ray beam intensity.

Answer 33

Number of photon energy passing through a object in 1 seconds.

Question 34

How can intensity be measured ?

Answer 34

Intensity = 1/distance2.

Question 35

How is intensity measured ?

Answer 35

Gys.

Question 36

If the distance is doubled from x-ray source, what would the intensity be ?

Answer 36

1/4 of the dosage.