Basic physics and electricity Flashcards
What is the first law of thermodynamics?
Energy can neither be created nor destroyed, but it can change form
What are the various forms of energy?
- kinetic
- chemical
- electrical
- magnetism
- heat
- sound
- potential
- nuclear
The further away from the nucleus an electron is, the more _______ held by the nucleus it is and therefore the _____ energy they have to use to hold on
- loosely
- more
Theremovalofanorbitalelectronfromanatom resultinginanetchangeintheatom’schargeand
expulsionofanelectron
Ionization
When does ionizing radiation occur?
When an atom is bombarded by energy sufficient to remove an electron from its orbit (energy applied must be greater than the electron:nucleus binding energy)
_____energiesarerequiredforoutershellelectronsthanforinnershellelectrons to ionize.
Lower
Radiation possesses characteristics of both _____ and _____.
Particle
Wave
The smallest unit of electromagnetic energy
photon
electromagnetic energy occurs in groups or “bundles of photons called….
quanta
X rays and visible light are both examples of what kind of energy?
electromagnetic energy
If X rays and visible light are both electromagnetic radiation, what makes X rays ionizing while visible light is not?
Xrays have much shorter wavelengths which gives them higher energy
Higher energy photons will have ______ (shorter/longer) wavelength.
shorter
Lower energy photons will have ______ (shorter/longer) wavelength.
longer
The velocity for ALL electromagnetic radiation is _______
the speed of light
How does the velocity of a 70 kV energy beam compare to the velocity of a 120 kV energy beam?
their velocities are the same
THIS WILL BE AN EXAM QUESTION
The higher energy beam has more penetrating power but it doesn’t get there any faster
Cannot be refracted by lenses or deflected by magnets
Describe the path of travel of an X-ray beam
they travel in a straight line at the speed of light….ALWAYS and stop only when they are absorbed
The differential penetration of matter is determined by what?
the mass or density of the matter
absorption: metal > bone > water > fat > air
Direct current
polarity of power source is constant and current flows from negative to positive, one direction only.
voltage is constant
Ex: batteries
alternating current
polarity of power source alternated between positive and negative at regular intervals causing a bidirectional flow of current
can achieve much higher voltages
Ex: outlets
What kind of current is required to run the components of the X-ray tube?
direct current, therefore the alternating current from the outlet must be converted to direct current by the transformer
What are the benefits of AC current?
- achieve higher voltages over greater distances
- generates less heat, therefore safer and less energy loss
- easier to modulate
What are the benefits of DC current?
- more consistent for delicate circuitry
- better for semiconductors, LED lights and solar power
The difference in electrical potential (polarity) between 2 locations in a circuit that cases electrical charges to flow through a circuit
electromotive force
The voltage measured at the peak of an electrical cycle in an X-ray tube circuit
kilovolts peak (kVp)
the flow of electrical charges in a circuit
current
The units used to describe the total quantity of electrical charges in a current?
coulombs
The unit for rate of flow of electrical charges
Amperes (1 Amp = 1 coulomb/1 sec)
In x-ray, cathode has what charge?
negative
In x-ray, anode has what charge?
positive
Where is the filament of an X-ray tube located?
on the cathode
What is the function of the filament in the X-ray tube?
The filament is heated by the cathode and then it emits a cloud of electrons which are accelerated towards the anode when a high voltage is applied to it. The high speed electrons will then strike metal on the anode and produce X-rays
What material is the metal plate and filament of an X-ray tube made of?
tungsten
What dictates the speed at which electrons will travel from the cathode to the anode in an X-ray tube?
The voltage (amount of energy) that is applied to the anode will accelerate the electrons. More speed = more X-rays produced when the electrons strike the metal anode plate
What does it mean to say the an X-ray tube is self rectifying in an AC current?
the X-ray tube prevents current from flowing from anode to cathode during half the electrical cycle
This is inefficient because X-rays are produced only during half of the electrical cycle in AC current
only 60 pulses per second would be useful, the other 60 would be wasted
What does half-wave rectification in AC current mean?
When a diode is placed to prevent electrons from flowing from + anode to - cathode during half the electrical cycle
in other words, it prevents back flow of electrons and essentially looks the same as a self rectifying circuit
What is a diode?
an electronic device that permits current to flow only in one direction and prevents back flow of current during the 2nd half of the wave
What does full wave rectification mean?
When 4 diodes are used in an AC current to redirect current (essentially create a U-turn) in circuit so that electricity is going from negative to positive during the whole cycle.
This doubles the useful pulses per second to 120 pulses/sec.
What is the benefit of full wave rectified X-ray machines over half or self rectified X-ray machines?
They are more energy efficient, therefore it shortens the exposure times to half that required by self rectified or half rectified x-ray machines.
What is tri phase power?
three single phase waves superimposed and separated by fractions of seconds. creating three sine waves that travel in phase, tripling the # of peaks, yielding a wave form with 360 pulses per second
What is the benefit of tri phase power?
provides a more constant and efficient voltage source which generates more efficient x-rays. This reduces patient dose and exposure
How are capacitors used in high frequency generation for X-rays?
capacitors are used to store electricity that can be discharged at extremely high frequency. individual capacitors have limited storage, but in sufficient numbers they can create a beam of energy at nearly peak output
What is the function of inverter circuits in high frequency generation?
they convert rectified AC current into a series of square pulses
Which is more powerful, triphase generator or high frequency generator?
triphase, and therefore it is more expensive
What is the benefit of high frequency generators over triphase generators?
They are far less expensive and take up less space and because they produce near peak voltage output, they are nearly as powerful has triphase
What would necessitate a triphase generator over a high frequency generator?
a very large patient (BMI >60)
a triphase output would be required to obtain a quality image
What is the cause of the pattern of exposure on an X-ray film?
differential penetration that results in a pattern in the remnant radiation
What is the radiation source in an X-ray?
the X-ray tube
What is remnant radiation?
remnant radiation is those photons from the primary radiation that were not absorbed as they traveled through the patient and will contribute to the production of an image.
What is secondary radiation?
secondary radiation is scatter radiation that results from primary radiation interacting with matter (target tissue). It does not contribute to the production of an image, travels in all directions and has less energy than the primary radiation that created it
What is primary radiation?
the cone shaped X-ray beam that is shaped and sized by the collimator before it leaves the tube and is unattenuated
The binding energy of electrons is greatest in _____, resulting in higher energy photons when
they are ejected during characteristic radiation production
inner (K shell) electrons
All Ionizing radiation has a wavelength of less than ______
1 nanometer
the removal of an orbital electron from an atom resulting in a net change in the atom’s charge
Ionization
Therapeutic radiation has the _____ (shortest/longest) wavelength, _____ (lowest/highest) energy and _____ (least/most) penetrating power.
- shortest
- highest
- most
Order, in decreasing energy, the following ionizing radiation particles:
Therapeutic radiation
X-rays
Gamma rays
Therapeutic radiation
Gamma rays
X-rays
The shortest wavelength non-ionizing electromagnetic waveform is
ultraviolet radiation
