Physics Basics Flashcards
What are the 7 properties of X-rays ?
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.
What will a X-rays wavelength, frequency and energy look like in comparison to other electromagnetic radiations ?
High frequency.
Short wavelength.
High energy.
Define frequency.
How many times wave shape repeats itself in one unit time.
What is frequency measured in ?
Hz
i.e. 1 cycle in one second = 1Hz.
Define wavelength.
Distance over which wave shape repeats itself.
What is wavelength measured in ?
Metres.
How can speed be calculated from wavelength and frequency ?
Speed = wavelength x frequency.
What speed do x-rays travel at ?
Speed of light - 3x108ms-1.
What are photons ?
Smallest possible packets of EM energy.
What do X-ray photon energies range between ?
124eV to 124keV.
What type of x-rays are used in dentistry and medicine ?
Hard x-rays.
What is the difference between hard and soft x-rays ?
Hard have higher energies.
What is the minimum energy of hard x-ray ?
> 5keV.
Describe how x-rays are produced.
- Electrons fired at atoms at high speed.
- On collision, kinetic energy of electrons is converted to electromagnetic x-rays and heat.
- X-ray photons are then aimed at subject.
What is the atomic number of tungsten atom ?
74 i.e. no. of protons.
What is the mass of tungsten atom ?
184 i.e. no. of protons and neutrons as their mass = 1.
Describe an atom in ‘ground state’.
Number of electrons = number of protons so neutral charge.
Describe ionisation.
Loss or addition of electron to atom.
Define binding energy.
Additional energy required to exceed electrostatic force i.e. remove electron.
What are the 5 components of an X-ray tube ?
Tubehead.
Collimator.
Positioning arm.
Circulatory.
Control panel.
Define current.
Flow of electric charge by movement of electrons.
What is current measured in ?
Amps i.e. how much charge flows by point in one second.
Describe direct current (DC).
Unidirectional flow of charge.
Describe alternating current (AC).
Constant reversal of direction of charge.
What are Hz ?
Cycles of reversal of direct of charge in AC per second.
What is mains AC Hz in UK ?
50Hz.
What is the process of changing mains AC to DC for purpose of x-ray called ?
Rectification.
What voltages do x-rays requires ?
2x types of voltage.
10kV and 10V.
Where in the xray machines are transformers required ?
Mains to X-ray tube.
Mains to filament.
What is a step up transformer used for ?
Increasing potential difference across X-ray tube to 60kV-70kV.
Reduce current to mA.
What is a step down transformer used for ?
Decreasing potential difference across filament to 10V.
10A.
Describe the pathway a xray beam takes ?
Travels in straight line but diverges from x-ray source.
Define x-ray beam intensity.
Number of photon energy passing through a object in 1 seconds.
How can intensity be measured ?
Intensity = 1/distance2.
How is intensity measured ?
Gys.
If the distance is doubled from x-ray source, what would the intensity be ?
1/4 of the dosage.
