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Physics Midterm

LCCC 117

WTF is This?No Shit Sherlock
Anode Cooling Curve Shows time needed for ANODE to cool
Tube Rating Chart Shows max technique factors (kVp and T for given mA)
HU Formula HU=kVp x mA x T x FACTOR x # Exposures
Single Phase HU Factor 1
3-Phase 6-Pulse HU Factor 1.35
3-Phase 12-Pulse HU Factor 1.41
High-Frequency HU Factor 1.45
What creates "ghost" images/shapes outside the collimated focal spot? Off Focus (Extrafocal) Radiation
What is average ROTOR RPM? What is RPM for high speed Rotor? 3,000-3,500 RPM Typical 10,000-12,000 RPM Hi Speed
Induction motor (________) located outside the Xray tube? Stator (Electromagnet pairs)
Tube Angle Coverage Formula? C = SID x tanTA x 2
Focal Spot is bigger at Anode end True or False False - Focal spot smaller at Anode, Bigger at Cathode
More photons at Anode end True or False False - Anode Heel Effect = Less Xrays at Anode end
Line Focus Principle Effective focal spot always smaller than Actual focal spot when angle <45°
Why is a sharper Target Angle better? 1. Greater area to dissipate heat 2. More focused Effective area
Actual Focal Spot Point on anode where Xrays are produced
Effective Focal Spot Functional portion of Xray beam (Central Ray)
3 Reasons Tungsten ideal 1. High Melting Point 2. High Atomic # 3. Good Heat Conduction
Rotating Anode made of? Tungsten alloy embedded in MOLYBDENUM Disc
Stationary Anode made of? Used primarily where? Tungsten alloy embedded in COPPER Low power DENTAL application
What type of Xray tube INCREASES the negative voltage of the focusing cup to control exposure? Grid-Biased (Grid Controlled) Tube
What voltage is used to restrict e- production in Grid-Biased tubes? Where are these used? -50 Volts Used in Cardiac Cath Labs
Max mA output due to Space Charge Effect? 1,000-1,200 mA
Why are Xray tubes limited on mA output? Why not 2,000 mA? Space Charge Effect
Ohm's Law V=IR Volts=Amps x Resistance
Unit of Radioactivity? Curie or Bequerels
Regulated max for Leakage Radiation? 100 mR/hr at 1 meter
What is a series of variable resistors? mA Selector
Selonoid vs Electromagnet Selonoid just Coil Electromagnet is Coil around FERROMAGNET Core
What is the exit point for Xrays from the Glass Envelope? Window
What is the window made of in Molybdenum Tubes? Beryllium (Mammography tubes)
3 Causes of Tube Failure 1. Arcing from Tungsten deposits on glass 2. Filament Breakage 3. Bearing Failure
Thermionic Emission Boiling of electrons
Minimum Response Time for AEC? 15-25 ms (Less common 5-6 ms)
AEC Backup Timer overrides and terminates exposure at ____ ? 6 sec or 600 mAs
Which AEC used a Fluorescent screen and Photomultiplier Tube to charge a capacitor to terminate exposure? Phototimer
What amperage does the mA selector supply to the tube? 3-6 amps
What converts AC to DC? Rectifier (Diode, SCR) Usually 1-4+ used
In the Xray Tube Circuit, what provides a constant turns ratio to make kVp? Step Up Transformer (Fixed High Voltage) Ex. 500:1 Gives 40-150 kVp
Which type of timer is used with falling load or battery powered portables? mAs Timer
What does a mAs Timer monitor to end exposure? Time & mA for mAs
Electronic Timer uses __________ and is accurate down to _____ ? Capacitors, 1 ms
Which timer is synchronized to the Electrical Waveform? How is time measured? Synchronous Motor, 1/120 sec = 8 ms
What reads incoming Voltage and Displays expected kVp Output? kVp Meter
Primary Voltage of High Voltage Transformer comes from? Secondary Voltage (Vs) of Autotransformer becomes Primary Voltage (Vp) of High Voltage Transformer
What adjusts for changes in voltage supplied to the generator? Line Compensator
3 Phase 6 Pulse Ripple? 3 Phase 12 Pulse Ripple? 13%, 3%
Converts AC to PULSED DC Current? Rectification
High Frequency Generator Ripple? <3%
Full Wave Rectification (FWR) uses how many diodes? Produces how many pulses? FWR 4 Rectifiers 120 pulses/sec
Half Wave Rectification (HWR) uses how many diodes? Produces how many pulses? HWR 1 Diode/Rectifier 60 pulses/sec
Converts 60 Hz AC to HiFreq pulsed DC... Hi-Freq Generator -
2 Connection Types for Three Phase Power? Delta and Wye (Y)
Diode that only allows electron flow in ONE Direction Rectifier
Turns Ratio Ns/Np
Voltage is Directly related to Turns Ratio T/F? True Ns/Np=Vs/Vp
Amperage is Directly related to Turns Ration T/F? False - Inversely Ip/Is=Ns/Np
VpIp = VsIs Current related to Voltage = Power conserved
Rotor Located in Anode Stem tries to align to STATOR's electromagnets
Sequential Activation STATOR's electromagnet pairs fire opposite in circle
Anode Rotation Rate? 3,500-10,000 rpm
Generator Convert Mechanical Energy to Electric Energy
Motor Electricity supplied creates Mechanical Energy
Mutual Induction Varying Electric current flows thru Electromagnet of Primary coil will INDUCE similar current in Secondary coil
Faraday's Law Electric Current induced in Circuit if some part in changing Magnetic Field
Total Current in Parallel Circuit It = I1+I2+I3
Total Voltage in Parallel Circuit Vt = V1 = V2 = V3
Total Resistance in Parallel Circuit 1/Rt = 1/R1 + 1/R2 + 1/R3
Rt in Parallel Circuit is always Less than ___ ? Rt < Any individual R
Total Resistance in Series Circuit Rt = R1 + R2 + R3
Total Current in Series Circuit It = I1 = I2 = I3
Total Voltage is a Series Circuit Vt = V1 + V2 + V3
kilowatt formula kW = (kV x mA)/1,000
Insulator (example) Does not allow electron flow (Glass)
Conductor (example) Electrons flow easily (Copper)
Semiconductor (example) Electrons flow in ONE Direction (Silicon)
Superconductor (example) Conduct w Less Resistance at LOW temps (Titanium)
Electric Current flows from ____ to ____ Current from + to -
Electrons flow from ____ to ____ Electrons from - to +
3 ways to Electrify an Object Friction, Contact, Induction
Coulumb's Law F = k (QaQb/d2) F = Force k = Coulumb's constant
Charges reside on the OUTER surface of ___ ? Conductors
Charges are dispersed evenly throughout ___ ? Insulators
All charges move along conductors T/F ? False - Only Negative
Photon Energy Formula E = hf Where f=frequency, h=Plank's constant
Wave Equation V=fλ Where V always speed of light
Wavelength (λ) of Xrays Xrays 0.1-.5 Angstroms
Autotransformers operate on what principle? Self-Induction
As Voltage _____ Current _____ Increases, Decreases
What transformer is used in the Filament Circuit? Step Down
Step Down transformer is used to? Decrease Voltage, Increase Amperage (Current)
Step Up transformer does what? Increase Voltage, Decrease Current
Transformers do what? Increase and Decrease Voltage (or electric potential) through electromagnetic Induction
Atomic Number (Z) # Protons
Atomic Mass (A) # Protons AND Neutrons
Force that keeps electons bound to shells? Centripetal Force
Created by: RadTechTKD