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Physics module 6
| Question | Answer |
|---|---|
| Primary circuit | That part of the x-ray equipment's circuitry that increases the supplied 220 volts to the level necessary for producing x-rays in conjunction with the secondary circuit |
| Secondary circuit | The x-ray tube circuit that increases the voltage to the kilovoltage needed to produce x-rays. It also rectifies the current from AC to DC as is needed for powering the x-ray tube. The tube itself is also considered part of the secondary circuit. |
| Filament circuit | The electric circuit to produce the heating current, in the region of 5A at the voltage of 12V, to the filament wire of an X ray tube filament circuit |
| Circuit breaker | A device that acts in the same manner as a fuse. Circuit breakers protect against short circuits and shock hazards. |
| Autotransformer | A device that raises or lowers voltage in the primary circuit, depending on the setting chosen on the machine's control panel for the kilovolt peak voltage (kVp) |
| Timer circuit | A circuit made up of a mechanical or electronic device whose action is to start and stop the high voltage across the x-ray tube. It is nearly always located in the primary section |
| Step-up transformer | A device in the primary circuit that raises voltage to the kilovolt level needed to power the x-ray tube. A very high voltage is needed to produce x-rays. The primary coil is in the primary circuit, the secondary coil in the secondary circuit. |
| Transformer | A device that operates on the principle of electromagnetic mutual induction to change the electric potential to a higher or lower voltage; also raises or lowers the current. Transformers are used for this purpose in x-ray equipment circuitry. |
| Line compensator | A device that incorporates a meter to measure the voltage provided to the x-ray imaging system and a control to adjust that voltage to precisely 220V |
| mA meter | A device placed in the tube circuit and used to monitor x-ray tube current. The x-ray imaging system |
| Rectifiers | A device that converts alternating current to direct current by allowing the current to flow through it in only one direction |
| X-ray tube | Glass vacuum bulb containing two electrodes. Electrons are obtained either from gas in the tube or from a heated cathode. |
| Rheostat | An appliance for regulating the resistance and thus controlling the amount of current entering an electric circuit |
| Step-down transformer | A device included in the filament circuit to lower the voltage to the filament. |
| Voltage | The unit of measurement (abbreviated as V) for electric potential; the difference in electric potential between two points |
| Alternating current (AC) | The type of current in which electrons alternate direction of flow as the electric potential switches back and forth |
| Current | The stream of electricity that moves along a conductor (Symbol I). An electric current is due to a difference of potential between two points, this difference being measured in volts. |
| Mutual induction | The phenomenon in which a current in one conductor induces a current to flow in another conductor. |
| Transformer law | The principle that there is a direct proportion between the ratio of wire turns and the ratio of voltage |
| Kilovolt peak (kVp) | The highest kilovolt (kV) value at which an x-ray exposure will be made; an adjustment the radiographer makes at the x-ray machine console |
| kVp setting | A setting that controls the electric potential difference between the cathode and the anode. Higher kVp settings give the projectile electrons greater kinetic energy and produce a beam with x-rays of greater quantity and quality. |
| mA | Current measured in milliamps (mA) is one of three variables the radiographer adjusts on the control panel when making an x-ray exposure. |
| With which transformer type would a radiographer be more interested in the output current? | Step-down transformer |
| Which transformer generally serves as the kVp selector? | Autotransformer |
| If a transformer has a turns ratio of 25/1 and 120V is applied to the primary coil, what will the output voltage be? | 3000 (25 x 120) |
| With the step-up transformer used in the x-ray circuit as the high tension transformer, what is the general increase in voltage? | About 500 times |
| Anode | The positively charged disc at one end of a vacuum tube; the disc in an x-ray tube, positively charged relative to the cathode; electrons from the cathode strike the tungsten target of the anode and produce x-rays |
| Cathode | The negatively charged element in a vacuum tube or x-ray tube |
| Insulator | A substance that does not conduct electric current because its electrons are bound within the molecules and cannot freely move. |
| Solid-state rectifier | A device used to create a powerful direct current from the supplied alternating current. Contemporary x-ray equipment uses solid state rectifiers. |
| Semi-conducting crystals | Type of material "in between" an insulator and a conductor. Some current flow does occur, but with special characteristics. |
| p-type crystal | A semiconductor based on a silicon lattice, which has boron atoms mixed in place of some of the silicon atoms. Since boron atoms have only three electrons in each of their outer shells, there is now a "hole" where an electron is missing. |
| n-type crystal | A semiconductor with a few free electrons in its lattice. It can be made by combining silicon, which has four electrons in its outer shell, with phosphorus, which has five electrons in its outer shell. The fifth phosphorus electron is free to move |
| Solid-state diode | A rectifier that is made by putting together n-type and p-type semiconductors in a device called a diode. The semiconductor diode is a rectifier because it allows current to flow in only one direction. |
| Full-wave rectification | A means of using all of an alternating current that is converted to direct current. |
| Three-phase power | The generation of three simultaneous voltage waveforms out of step with one another, thus never dropping the voltage to zero during exposure. |
| High frequency generator | An X ray generator providing a nearly constant high voltage waveform for the X ray tube |
| Electrons flow in which direction in relation to the solid-state rectifier symbol? | Against the arrow |
| Which waveform has the lest voltage ripple? | High frequency |
| How many rectifiers are necessary to create a single-phase full wave waveform? | 4 |
| Which type of current is necessary for rectifiers to operate? | Not dependent on current type |
| Resistance | The ability of an element in a circuit to resist the flow of electricity by reducing or impeding it |
| Resistors | An appliance for regulating the resistance and thus controlling the amount of current entering an electric circuit |
| Exposure timer | A device that regulates the length of time the electrons are allowed to cross the tube and, therefore, the time x-rays are produced to create a radiographic image. |
| Synchronous timer | A timing mechanism based on a synchronous motor that drives a shaft at precisely 60 revolutions per second |
| Synchronous motor | A precision device designed to drive a shat at precisely 60 revolutions per second synchronous motor |
| Electronic timer | Timing circuit based on the time required to charge a capacitor through a variable resistor |
| mAs timer | A special kind of electronic timer that monitors the product of mA and exposure time and terminates the exposure when the desired mAs value is attained |
| Automatic exposure control (AEC) | A device that controls image density by terminating the exposure at a preset density level, automatically adjusting exposures according to patient thickness |
| Phototimer | A device used in radiology and photography to control the exposure interval by terminating the exposure when the amount of incident radiation or light reaches a preset quantity |
| Ionization chamber | A device for measuring ionizing radiation by the measurement of the ionization of the gas contained in the chamber |
| Ionization | The process of turning an atom into an ion by adding or removing an electron. In either case, the change in the number of electrons changes the electrical charge of the atom. |
| The lower the mA station number the greater the resistance in a filament circuit. T or F | True |
| Which exposure timer has the patient as the variable? | Phototimer (AEC) |
| What exposure timer incorporates a variable resister? | Electronic timer |
| Focal spot | The part of the target of an x-ray tube which is bombarded by the focused electron stream when the tube is energized |
| Self induction | The process that occurs in a single coil of wire when an alternating current flows through it; the flow of electrons in one direction produces a magnetic field that induces a second current to flow in the wire, but in the opposite direction |
| Focusing cup | A shell-like device behind and to the sides of the filament that prevents spreading of the electrons as they move from the filament toward the anode |
| The filament circuit controls what part of the x-ray tube? | Filament |
| Self induction is a part of which of the following? | Autotransformer |
| The large kilovoltage creates a large positive charge on which of the following? | Anode |
| What serves to route power through the x-ray tube in the desired direction? | Rectifier |
| What characteristic of alternating current is important to transformer operation? | Fluctuating magnetic field |
| The process by which a transformer increases or decreases voltage is called: | Mutual induction |
| Which of the following best describes the autotransformer? | One coil serving as both primary and secondary |
| The step-up transformer serves what purpose in the general x-ray circuit? | Increases voltage to kV needed for x-ray production |
| A step-down transformer is used in the filament current for what purpose? | Protect the filament by decreasing voltage |
| What is the output voltage of a transformer with 30 coils in the primary and 90 coils in the secondary when 120 volts is applied? | 360 (vS/120=90/30) |
| How many turns are needed in the secondary to produce 200 volts if there are 10 turns in the primary and 20 volts is applied? | 100 (200/20=Ns/10) |
| Why are rectifiers necessary in the general x-ray circuit? | Because the tube operates best when current flows from anode to cathode |
| Which of the following accurately describes the solid-state rectifier? | A p-n crystal that only conducts electricity in one direction |
| Which direction does current flow through a solid-state rectifier? | With the direction of the arrow of the solid-state rectifier |
| With four rectifiers and one waveform, what is the voltage ripple? | 100% |
| When the negative half of each AC cycle is suppressed we are left with which of the following? | Single-phase half wave |
| The rheostat controls which of the following in the filament circuit? | Resistance |
| The technologist has direct control of the resistance in the filament circuit through which setting on the control panel? | mA station |
| Which of the following technique settings will have the highest resistance in the filament circuit? | 70 kV @ 10 mA |
| Why are rheostats necessary in the x-ray production process? | Control filament heating |
| The exposure timer serves what purpose in the general x-ray circuit? | Controls duration of filament heating |
| Which exposure timer is based on how fast a motor turns a shaft? | Synchronous timer |
| Which sections provide the kinetic energy needed to produce x-rays? | Primary and secondary |
| Which component serves to route electricity through the x-ray tube in the same direction each time? | Rectifier |
| Which component increases voltage about 500 times? | Step-up transformer |
Created by:
volcomgrl12