Chap 4 Electromagnetism
If a transformer is supplied with 16 volts and 4 amperes, the output current from this transformer with an output voltage of 1200 volts would be
.05 amperes
American generators operate at
60 Hz
How many times does an AC current change direction in a single minute?
7,200
For a simple AC generator, the value of the induced voltage in the armature loop is maximum when the orientation of the armature as compared to the magnetic field is
90 degrees
a series of easily remembered aids to help with the relationship between electricity and magnetism
Fleming's hand rules
results from the inherent resistance to current flow that is found in all conductors; power lost from resistance is proportional to the square of current; sometimes called copper loss
I^2R loss
A simple DC generator has essentially the same construction as an AC generator except that a DC generator employs the use of
a commutator
A transformer with more secondary windings than primary windings has
a greater secondary voltage
arrangement of two coils of wire in proximity to facilitate induction
air- core transformer
a device used to measure current connected in a series; measured in amps
ammeter
a coil of wire that acts as aconductor
armature
manufactured from steel alloy called alnico, composed of aluminum, nickel, and cobalt
artificial permanent magnet
a transformer that automatically sets by adjustments
autotransformer
a device, attached to slip rings, that allows the circuit to remain stationary while the armature rotates without breaking the electrical contact between them
brush
All of the following are true of induction motors EXCEPT a. They use multiphase current and can turn at varying rpm. b. Motor power can be regulated by the characteristics of the electromagnets that make up the stator c. Their design is inherently weak with regard to power d. They are used to spin the x-ray tube anode disk
c. Their design is inherently weak with regard to power
All of the following are true of transformers EXCEPT a. They have no moving parts b. They work on the principle of mutual induction c. They work most efficiently on pulsating DC d. They are designed to regulate voltage
c. They work most efficiently on pulsating DC
A diode electron tube such as a valve tube
can be used for rectification
An induced current in a wire loop
can result only from an alternately expanding and contrasting magnetic field
An electrical device that is designed to store charge momentarily after charging is a
capacitor
a device capable of accumulating and storing an electrical charge
capacitor
arrangement of two coils of wire each filled with an iron core in proximity to facilitate induction that converges the inside and outside lines of force through the core
closed-core transformer
the energy that causes reorientation of the magnetic dipoles
coercivity
a single ring that is divided in half, with each half connected to one end of the armature wire
commutator ring
A rectifier
converts AC to DC
Electrons move downward in a vertical wire. The direction of associated magnetic field directly around the wire is
counter clockwise
All of the following are true of autotransformers EXCEPT a. They are considered a variable transformer b. The primary and secondary coils are in series c. The primary and secondary windings share a common coil d. They are effective in controlling voltage on the high voltage side of circuit
d. They are effective in controlling voltage on the high voltage side of circuit
materials weakly repelled by all magnetic fields
diamagnetic
the insulation between two plates in a capacitor
dielectric
a rectifying semiconductor made by sandwiching p-type crystal with an n-type to form a p-n junction
diode
used to measure alternating current when electromagnets are used
dynamometer
result of currents opposing the cause that produced them
eddy current loss
A magnetic field is produced by
electric charges in motion
A motor is a device that converts
electrical energy into mechanical energy
temporary magnet produced by moving electric current
electromagnet
a device used to protect the radiographer from electric shock by isolating control buttons on the x-ray console from the actual circuit in which high voltage is flowing
electromagnetic relay
a stator consists of
electromagnets
the unit of capacitance
fared(f)
materials that are highly permeable and susceptible to induction
ferromagnetic
determined by field strength and the arc in which the lines of flux are located
flux density
Conventional current flows
from anode to cathode
the conversion of the opposing half of the incoming electron flow to always move in the same direction, instead of discarding half the cycle
full-wave rectification
used to measure direct current when permanent magnets are used
galvanometer
the unit used for measuring magnetic flux density
gauss (g)
a device that converts mechanical energy to electrical energy using moving lines of flux in relationship to a conductor to induce current; also known as a dynamo
generator
suppressed rectification resulting from only half of the incoming alternating current being converted to pulsating direct current; called self- rectification
half-wave rectification
results from energy expended as the continually changing AC current magnetizes, demagnetizes, and remagnetizes the core material; also called lagging loss
hysteresis loss
the ability of an alternating current to switch directions, causing the opposing potential difference to induce against the incoming supply of electrons; measured in ohms of resistance
inductive reactance
The magnetic flux through a wire loop
is maximum when the plane of the loop is perpendicular to the magnetic field
the inherent power loss of electrical conduction through solid wire conductors
is minimized with higher voltage transmission
the force fields that are created when magnetic dipoles orient to create a magnet; also known as lines of force & magnetic field
lines of flux
the force fields that are created when magnetic dipoles orient to create a magnet; also known as lines of flux & magnetic field
lines of force
an object that exhibits a uniformly strong magnetic field
magnet
groups of atoms that their net magnetic field moving in the same direction; also know as magnetic domains
magnetic dipole
groups of atoms that their net magnetic field moving in the same direction; also know as magnetic dipole
magnetic domain
the force fields that are created when magnetic diploes orient to create a magnet; also know as lines of flux and lines of force
magnetic field
A generator is a device that converts
mechanical energy to electrical energy
a device that is supplied with electrical current to produce mechanical motion
motor
The magnitude of force felt by a moving charge through a magnetic field would be LEAST if the charge were
moving directly into the magnetic field & moving directly away from the magnetic field
the result of two coils being placed in close proximity with a varying current supplied to the first coil, which then induces a similar flow in the second coil
mutual induction
The charge carriers are considered to be a negative in a
n-type semiconductor
created when iron oxide remains in the earth's magnetic field for ages, slowly orienting the magnetic diploes in the same direction
natural magnet
An alternately expanding and contracting magnetic field is produced by a. a stationary magnet b. a steady current flowing c. a battery d. none of the above
none of above
materials not affected by magnetic fields and that cannot be magnetized(wood, glass, rubber, plastic)
nonmagnetic
The turns ratio of a transformer is determined by the
number of windings
arrangement of two coils of wire each filled with an iron core in proximity to facilitate induction
open-core transformer
the motion of a charged creates a magnetic force field perpendicular to the motion
orbital magnetic moment
materials that have a low permeability and weak attraction to magnetic fields(aluminum)
paramagnetic
the ease with which a material can be magnetized
permeability
the coil first supplied with the current
primary coil
the process by which alternating current is changed to pulsating direct current
rectification
When using alternating current,
resistance is calculated as impedance (Z) & electrical production can be graphically expressed as a sinusoidal wave
the ability of a material to stay magnitized
retentivity
a hollow copper cylinder or cuff that is attached to the anode disk by a molybdenum shaft
rotor
the coil in which a current is inducted by the primary coil
secondary coil
the ability of alternating current to switch direction, causing a opposing potential difference to induce against the incoming supply of electrons; allows direct current to flow while at the same time hindering alternating current
self-induction
suppressed rectification resulting from only half of the incoming alternating current being converted to pulsating direct current; called half-wave rectification
self-rectification
arrangement of two coils of wire each filled with an iron core in proximity to facilitate induction
shell-type transformer
The material of choice for semiconductors is
silicon
a complex semiconductor useful for high-speed switching of the primary high-voltage x-ray circuit; also known as a thyristor
silicon-controlled rectifier (SCR)
the type of curve produced by an AC generator
sine wave
a device with attached brushes that allows the circuit to remain stationary while the armature rotates without breaking the electrical contact between them
slip ring
a coil consisting of a series of loops, which serve to increase the flux density
solenoid
as more and more electrons build up in the area of the filament, their negative charges begin to oppose the emission of additional electrons
space charge cloud
the magnetic effect created by electrons spinning on their axes
spin magnetic moment
induction motor electromagnets that turn the anode
stator
a device used to decrease the voltage from the primary to the secondary coil
step-down transformer
a device used to increase the voltage from the primary to the secondary coil
step-up transformer
the unit used for measuring magnetic flux density
tesla
The efficiency of a transformer is not affected by
the transformer turns ratio
The process of electrons being emitted from heated metallic surfaces is called
thermionic emission
the ejection of electrons from the surface of the wire to increase heat, causing an electron cloud; also called the space cloud charge
thermionic emission
a complex semiconductor useful for high-speed switching of the primary high-voltage x-ray circuit; also known as silicon controlled rectifier
thyristor
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; this serves to either increase or decrease the voltage
transformer
when the voltage is increased from primary to secondary it is step-up transformer. when decreased from primary to secondary it is calls step-down transformer
transformer law Vs/Vp=Ns/Np
a device used to measure current connected in parallel ; measure potential difference in volts
voltmeter
SI unit to measure magnetic flux
weber(Wb)
A bar magnet and a wire loop move with the same linear velocity and direction. what is the voltage induced in the wire?
zero