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