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RADR-2209 U3 Magnetism, Transformers, & Current Trace.
Terms in this set (117)
In reference to Magnetism, the earth is a natural __________?
hard steel and alloys
Artificial magnets are usually made of what type of material?
basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets
the measure of the ability of a material to support the formation of a magnetic field within itself
term for the production of
voltage and current in a conductor whenever a magnetic field is passed over the conductor or if
the conductor is passed through a magnetic field
Sometimes when a strong magnet is placed alongside a non magnetized but
magnetically permeable material, the non magnetized material can become a magnet
(The strength of the magnet will dictate the amount of flux
associated with a magnet)
refers to the magnetic field that is associated with magnets (lines of force)
the ability of a material to remain a magnet
metals that are only slightly magnetic
materials that are actually repelled by
Pole in a magnet
Any magnet will have two of these, a north and a south ________
perpendicular to the
direction of motion
An electron moving in a specific direction
will generate magnetic lines of force in what direction?
the science that studies the relationship between electricity and magnetism
This unique property of expanding lines of force when the electric current is turned on and the
collapsing of the lines of force when the current is turned off is also responsible for another
electrical property known as
solenoid or a helix
An electric coil is a device that is sometimes referred to as a
Each loop of a coil is called a "____" and the more
these there are, the greater the magnetic flux
The purpose of using this material is to intensify the magnetic flux even more
When an "_________________________" is used the
current and the magnetic field reverses itself rapidly many times per second.
A conductor must move across (cut) a magnetic field or
a magnetic field must move across (cut) a
To produce a pulse of voltage:
• Speed of the moving conductor
• Strength of magnetic field
• Angle of the cut
• No. of turns in the coiled
Factors That Determine The Level of Voltage
If there is no motion between the magnetic field and the conductor, there will be no production
of voltage and current in the conductor. T/F
Device that produces alternating
A device that maintains the same rotational speed is called a
One generator armature revolution is how many cycles
1 cycle = how many hertz
60 positive and 60 negative cycles for a total of 120.
In 1 sec. with 60 Hz (AC) current there are how many positive and negative cycles
U.S. households use how many Hz current?
Voltage, emf (electromotive force)
potential difference has two other terms that can be used interchangeably
When this is produced by direct current (DC), it is
referred to as ____ ___ because the voltage that is produced is going in the reverse direction and
opposes the forward flow of the electron current
the electrical phenomena that occurs when alternating current (AC)is used in a circuit which has a coil. (Opposition to flow as moving back and forward)
inductive reactance (XL)
The term _________ _________ is a type of resistance that is generated by a coil that is in an AC circuit
Batteries produce this type of power
the most efficient type of electrical current is
False. Begins to decline steadily, but not instantly. ( example: when you let off the gas in your car, it doesn't come to an immediate stop. It has to slow down first. This also goes for the "break" phase of electricity)
When the electric current is turned off (Break phase), the voltage amplitude begins to decline instantly. T/F
During the _____ phase, as the voltage climbs the
magnetic field will also increase and expand in size around the coil
The property that coils have to produce this type of resistance is called inductance and
the unit of inductance is the
step up transformer ( high voltage, or high tension transformer)
________ ____ _________________ is an electronic device
that increases voltage from one level to a higher level
_________ can increase volts to kilovolts
is a process where one coil of a transformer produces a magnetic field that
causes a pulse of voltage and current to be generated in the secondary coil of the transformer.
air-core and open-core transformers
The problem with these two transformers is that the magnetic flux leaks out of the ends of the transformers and it loses energy and efficiency
closed core and shell-type transformers
The conductor or coils are wrapped around an iron square which gives the magnetic flux a solid path to flow and these transformers are much more efficient and lose less power than the air-core and open-core transformers
transformer law equation
Vs = Ns
Vs= voltage in the secondary
Vp= voltage in the primary
Ns= number of turns in the secondary coil
Np= number of turns in the primary coil
False. The current will always be
stepped down on the secondary side of the transformer.
When voltage is stepped up on the secondary side of the transformer, the current will always be
stepped up on the secondary side of the transformer. T/F
Copper loss /I^2R Loss
This describes the simple resistance of copper or the conductor material that is used in
This occur as a result of currents opposing the cause that produced them and happen in
conducting material when there are constantly changing magnetic fields and also tend
to cause a loss of efficiency and they also create a voltage drop
This occurs because energy is expended as the AC current repeatedly magnetizes and demagnetizes
This is responsible for providing variable
voltage to the primary coils of the step up transformer and it allows the radiographer to control changes in kVp
This is defined as the conversion of standard alternating current (AC) into pulsating
direct current (DC)
property of an x-ray tube which means that it acts as a valve permitting the flow of current in only one direction, from the cathode to the anode
rectification system known as thermionic diode
a valve tube that has a filament and an anode (older of the systems)
Half-wave rectification tube
Type of Valve tube:
Electron flow during positive half cycle/
negative half cycle is suppression
Normal voltage drop of 1.5 kVp
solid state rectifiers
These are devices that are made of materials that are semiconductors and they work much more efficiently than valve tubes
Adding arsenic to silicon forms this type of silicon (solid state rectifier)
__________ is added to silicon to produce P-type silicon P-type silicon accepts electrons (solid state rectifier)
Solid state rectifiers
The p-type and N-type solid state devices are otherwise known as _________
One important observation is the fact that
the P-type silicon is contacting the cathode (N-type) . The point of contact is the _____ junction
False. Heat will not allow to make large exposures on S-Rec. x-ray tube
Because of the buildup of heat by the anode, the self-rectified x-ray tube will be able to make large exposures. T/F
True. Rectifiers will reduce heat load on circuit.
Placing the rectifier (Fig 2-1 R) between the x-ray tube and point Y will strategically help suppress the voltage and current as it moves from point Y toward the x-ray tube. T/F
With half-wave rectification of 60 Hz AC, there
are 60 positive pulses transmitted per second while 60 negative pulses are suppressed. T/F
because the negative pulses of voltage and current are always suppressed with half-wave rectification
Even when there are one or two rectifiers in HWR, 50% of the exposure is still wasted. Why?
Full rectified given the four rectifiers
This unit is a what type of rectification (Full, half,self) ?
Solid state rectifiers
This unit has what type of rectifiers (Look a the triangular shape diode)?
Positive half cycle. It produces the first up wave.
This image depicts what cycle as the current is produced? (look at the direction of travel.)
Negative half cycle. The polarities of X and Y have changed as compared to positive half. This produces the second wave
This image depicts what cycle as the current is produced? (look at the direction of travel.)
If a complete cycle is 1/60 of a second than that means that 2 waves equal 1/60 sec and one wave is 1/120th sec.
4 x 1/120sec = 4/120th or 1/30th of a second.
So it took 1/30th sec to produce example 1
and example 2: 1/20th sec to produce
In this 60Hz AC current, how long did it take to produce example 1 and example 2 in seconds?
The synchronous timer is a special type of motor that drives a shaft at 60 revolutions per second
(rps). The minimum exposure time possible with the synchronous timer is
electronic timer (Can create exposure times as fast as 1 ms)
The most sophisticated and most accurate timer in use today is the
This timer monitors the tube current
Which statement below is most closely associated with the term "electromagnetic induction"?
a. This term defines how magnetic flux is intensified
b. This describes how "magnetism" expands and collapses in a coil during the "on-phase"
c. This describes how the resistance of conductors will influence current and voltage drops
d. This term describes how an electric current/voltage is generated in a conductor by magnetism
The speed of the moving magnetic field.
The angle of the cut between the magnetic field and the conductor.
The intensity or number of the lines of force in the magnet.
According to Faraday's Law, which factors will influence the amount of current generated by a moving magnetic field as it interacts with a stationary conductor?
An EMF will be generated in the conductor during the expansion of magnetism
What happens if a magnetic field expands in the presence of a stationary conductor?
decreasing the diameter of the conductor used for the coils.
increasing the length of the conductor.
Copper losses in a transformer will increase under the following condition:
An element that is "diamagnetic" is
Self Induction occurs when expending magnetism generates a current/voltage pulse in the
opposite direction of the primary voltage in a coil.
When a coil is connected to either alternating current or direct current, a property
known as "self-Induction" occurs. The following statements describes best what self
As you are aware, when an electric current is being transmitted through a conductor, a magnetic field
is also generated along with the current/voltage. Based on Flemings rules (both the right hand and
left hand rules), which one of the following statements below is true?
a. If the current/voltage are steady, the magnetic field does not exist
b. If the current/voltage are AC, then the magnetic field develops "parallel" to the conductor
c. If the current/voltage is DC, then the magnetic field only exists parallel to the conductor
during the "make phase".
d. If the current/voltage are AC, then the magnetic field expands & contracts perpendicular to
Based on how electricity is generated, identify those conditions below that would generate voltage and current in a conductor.
1. Pulsating or varying the flux density of magnetism around a conductor.
2. Maintaining a steady magnetic field around a conductor.
3. Move the conductor at right angles through the magnetic field.
If alternating current has a frequency of 60 Hz, how many total pulses will this current exhibit in 1
During the "make" and "break" process of DC,
1. There is no magnetism present during the "on" phase.
2. The magnetism expands during the make phase.
3. Magnetism will collapse during the break phase.
not generate any Voltage
A steady magnetic field in the presence of a conductor will:
The voltage/current produced in the secondary coil of a transformer produces magnetism
that also generates an emf in the primary coil simultaneously. This is known as?
AC current passing through a coil
The term Inductive Reactance is caused by
The vertical Locks on the x-ray tube and collimator are components in the x-ray machine that make use of electromagnetism. T/F
Metals that are strongly attracted by magnets
Ferro-magnetic materials are
The electrical process of converting AC to pulsating DC
What is the best statement that describes or best defines the term "rectification" as used in
The amplitude refers to the height or peak of the voltage pulse
When describing an AC sine wave, what are we referring to when you describe the "amplitude"?
The normal resistance of the metal that is used in the coils of a transformer.
The electrical efficiency loss that results when the constantly changing magnetic fields affects
the core of a transformer.
Identify the factors which can reduce the "efficiency" of a transformer.
the spinning motion of an electron as it "orbits" around the nucleus of an atom
A magnetic dipole is generated by:
Insulate electrically and Help prevent the transformer from overheating
Transformers used in radiology equipment are characterized by having the primary and secondary coils immersed in oil. What is the purpose of this oil?
When coils are used in AC circuits, they perform functions such as generating a strong
magnetic field and also causing a reverse voltage which opposes the primary flow of the current
and voltage. This electrical process is called:
The gauss and Tesla.
Magnetic Flux Density may be measured by:
and shell type
The most common type of high tension transformer used in Radiology today is:
As you are aware, the primary coils of a "step-up" transformer are provided with a specific
amount of voltage and current. This combination of current and voltage may also be expressed
as "power" in watts. Assuming 100% efficiency, what would the power in the secondary
coils be if the primary voltage and current is 250 V at 40 amps?
If the transformer is a "step down" transformer, the voltage in the secondary coils will be
lower than in the primary coils and the current in the secondary will be higher than in the
helix, solinoid, or electric coil ( all the same)
The term "bucking EMF" is an expression of what happens in the following electrical device in an
The type of rectification that is least efficient in an x-ray system is:
What does the highest point in the sine wave represent?
In one half second (.5sec 60Hz), how many negative pulses will be generated?
8.3 mS or 1/120th
If two pulses are generated in 16.6 mS or 1/60TH of a second, how long does it take to generate one pulse?
one pulse is 8.3 mS
100mS/8.3mS= 12.05 or 12
Calculate the number of x-ray pulses that will be generated in 100 Ms. (FWR 60 Hz AC)
High Voltage Transformer and
Filament or step-down transformer
The operating principle known as "mutual induction" occurs with the
The operating principle known as "self-induction" occurs in the
Number of lines of force is measured by the "SI" unit known as
1. main breaker
2. exposure switch
4. timer circuit
5. High voltage step up transformer
6. 4 diode rectification system
Step-down filament transformer
Step up transformer
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