RT 205 Electromagnetism II Flashcards
Faraday’s Law: Methods to induce a current:
- Moving a permanent magnet into and out of a coil of wire also induced a current in the wire while the magnet was in motion.
- Moving a conductor near a stationary permanent magnet caused a current to flow in the wire, too, as it was moving.
- Made it possible to determine the direction of the induced current flow.
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Four factors of Faraday’s Law: The magnitude of the induced current depends on four factors.
- The strength of the magnetic field
- The velocity of the magnetic field as it moves past the conductor
- The angle of the conductor to magnetic field (lines of flux)
- The number of turns in the conductor
Lenz’s Law
An induced emf generates a current that induces a counter magnetic field that opposes the magnetic field generating the current. Name the law.
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The production of an electromotive force (emf) or voltage in an electric circuit caused by a changing magnetic flux in a neighboring circuit
Mutual Induction
Property whereby an electromotive force is induced in a circuit by a variation of current in the circuit itself
Self Induction
Opposition to the flow of AC current produced by an inductor; measured in ohms and varies in direct proportion to frequency
Inductive Reactance
Fleming’s Right Hand Generator Rules
Thumb: points in direction of conductor (armature) moves
Index finger: points in the direction of magnetic lines of force
Middle finger: Indicates the direction of conventional current flow
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Converts mechanical energy into electrical energy
Dynamo (Generator)
How is electricity produced in a dynamo?
From magnets whirling inside of coils of wire in the generator core.
Components of a Generator
Moving part of magnetic device consisting of one or more coils that are electrically connected to create a rotational section of a generator
Armature (Conductor)
Components of a Generator
Means of producing an electrical connection through a rotational assembly
Slip Rings
Components of a Generator
Conducts current between rotating stationary parts of a generator or motor
Brushes
Produced when wires motion relative to the lines of force is reversed
Alternating Current
1 Cycles per second (cps)= 1 Hz
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U.S. Generators utilize how many Hertz?
60 Hz (or 120 Changes per second)
Components of a Generator
A single ring that is divided in half, with each half connected to one end of the armature wire (Replaces pair of slip rings, produced direct current, keep current flowing in the same direction)
Commutator Ring
Converts electrical to mechanical energy
Motors
Fleming’s Left Hand Motor Rule
Thumb: Movement of Conductor on Rotor
Index: Magnetic lines of force field
Middle: Current or electron flow
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What type of rings do AC motors use?
Slip Rings
What type of rings do DC motors use?
Commutator rings
Types of motors
Synchronus Induction
Induction motor electromagnets that turn the anode; Supplied with multiphase current
Stator
Types of motors
Synchronus Induction
A hollow copper cyclinder or cuff that is attached to the anode disk by a molybdenum shaft (Used in rotating anode x-ray tubes)
Rotor
Measures Direct Current (Use permanent magnets)
Galvanometers
Measures Alternating Current (Use electromagnets)
Ammeter
Measures connected in parallel (Measure potential difference)
Voltmeter
A device in which two coils are placed near one another without electrical connection (The number of turns in the coils differs, causing a change in current in the secondary coil; Serves to either increase or decrease the voltage)
Transformers
Three causes of loss of efficiency in transformers:
First cause:Copper loss (I^2R loss)
1. Resistance in the wires (minimized by using low resistance wire.
2. Large diameter copper (Minimized by using high voltage and low amperage)
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Three causes of loss of efficiency in transformers:
Second cause: Hysteresis loss (lagging loss)
1. Results from energy expended as the continually changing AC current magnetizes, demagnetizes, and remagnetizes the core
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Three causes of loss of efficiency in transformers:
Third cause: Eddy current loss
1. Currents that oppose the magnetic field that induced them (laminating the core reduces this loss)
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Accumulates and stores an electrical charge (Two oppositely charged metal plated separated by dielectric)
Capacitors
A material that can sustain an electric field but does not conduct electric current
Dielectric
Capacitor Formula: C= Q/V C= capacitance of the capacitor Q= charge on one of the plates of the capacitor V= voltage across the capacitor
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What is capacitance measure in?
farads (F)
1F= 1Coulomb/Colt
This means how many coulombs of charge can be stored in a capacitor per volt in the power source
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The process of converting alternating current into a unidirectional current, by removing or inverting that part of the wave laying on one side of the zero amplitude axis
Rectification
A solid-state switching device for semiconductors to convert AC current in one of two directions controlled by an electrode
(Thyristor or silicon-controlled rectifier (SCR))
Solid-state diodes
A device that allows current to flow in one direction only (Produced by sandwiching n-type and p-type crystals
Diode
A cathode and anode separated so that electrons can only flow from cathode to anode
Vacuum tube type diode
Flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. The effect increases dramatically with increasing temperature (1000- 3000 K)
Thermionic Emmission
Another name for Thermionic emission?
Space charge cloud
Protects from current that can damage equipment?
Rectification
Rectifying process
Passes only one-half of each incoming sinusoid, and does not pass the opposite half cycle
Half-wave Rectification
Rectifying process
Passes the positive half and inverts the negative half cycle of the input sinusoid so that the output contains two half sine pulses for each input cycle
Full-wave Rectification
Main Circuit Parts of an x-ray machine:
The switch that generates the power to the x-ray tube
Main Switch
Main Circuit Parts of an x-ray machine:
A remote control device that permits current flow through the circuit
Exposure Switch
Main Circuit Parts of an x-ray machine:
Device used to end the exposure at an accurately measured preset time
Timer
Main Circuit Parts of an x-ray machine:
Where the alternating current comes form to power the circuit
Main breaker
Main Circuit Parts of an x-ray machine:
This is where you adjust the kVp for the exposure
Autotransformer
Main Circuit Parts of an x-ray machine:
This transformer bumps the voltage up so that the x-ray tube has very high voltage to make the electrons have enough energy to form x-rays
High-voltage step-up transformer
Main Circuit Parts of an x-ray machine:
This makes the current only go in one direction through the x-ray tube
Four-diode rectification circuit
Main Circuit Parts of an x-ray machine:
This variable resistor adjusts the current going to the filament
Filament circuit variable resistor
Main Circuit Parts of an x-ray machine:
This transformer steps the voltage down and therefore the current up.
Filament step-down transformer
Main Circuit Parts of an x-ray machine:
This is where the x-rays are created
X-ray tube
Main Circuit Parts of an x-ray machine:
This rotates the anode
Rotor Stator
