A/C, D/C, and Magnetism - Part 1
Earth contains magnetic poles.
True
_______________ materials are either metal or nonmetal materials that cannot be magnetized.
diamagnetic
_______________ materials are metals that are easily magnetized.
ferromagnetic
When a conductor cuts magnetic lines of force, a voltage is induced into the conductor. This principle is called _____.
Electromagnetic induction
When using the left-hand generator rule, the thumb points to the direction of _____.
Thrust
The horsepower rating of three-phase motors and the kilovolt-ampere rating of three-phase transformers are about _____ greater than for single-phase motors or transformers with a similar frame size.
150%
A basic law of magnetism states that unlike poles _____ and like poles _____.
Attract, repel.
Electrons can form spin patterns that _____ the magnetic field of the material.
Cancel
The angular difference between true north and magnetic north is known as the angle of _____.
Declination
If an object is placed in the field of an strong electromagnet connected to an AC line, the object will be _____.
Demagnetized
The direction of induced current can be determined by using the _____ left-hand generator rule.
Fleming
A magnet that produces a magnetic field as long as current is flowing is called a(n) _____ magnet.
Electromagnets
Magnetism can be explained in terms of _____ spin patterns.
Electrons
In three-phase power systems, the delivered power _____.
Never falls to zero
_____ do not require any power of force to maintain their field.
Permanent magnets
Magnetic lines of force are called _____.
Flux
The three substances that form natural magnets are _____.
Iron, nickel, and cobalt.
If current is flowing in a circuit containing an inductor and the power switch is opened, the magnetic filed surrounding the inductor collapses and induces voltage into the inductor, resulting in a voltage spike.
True
Man-made permanent magnets retain their magnetism _____ than natural magnets.
Longer
Lodestone is a name for a naturally occurring magnetic material that is also called _____.
Magnetite
The measure of a material's ability to be magnetized is called _____.
Permeability
The time required for current in an inductor to reach its full Ohm's law value is called the _____ time constant.
R-L
The measure of a material's resistance to magnetism is _____.
Reluctance
The north magnetic pole of a compass needle is attracted to the _____ magnetic pole of the earth.
South
The amount of voltage induced into a conductor depends on the turns of wire, the strength of the magnetic field, and the speed of cutting action.
True
In the English system of measure, magnetic strength is measured in a term called _____."
Flux density
When a magnetic materials molecules are all lined up, and increases in current flow no longer cause increases in magnetic field strength, the material has reached _____.
Saturation
The north pole of a compass needle points in the direction of the south geographic pole.
True
To locate the north pole of an electromagnet, use the _____ hand rule.
left
The amount of magnetism left in a material after the magnetizing force has stopped is called _____.
residual magnetism
If a voltage is being induced into a conductor by electromagnetic induction, reversing the direction of motion of the conductor will _____.
reverse the polarity of the induced voltage
The strength of an electromagnet is primarily proportional to its _____.
ampere-turns
When using the left-hand generator rule, the center finger points to the direction of _____.
Flux
A way of determining the relationships of the motion of the conductor, the magnetic field direction, and the direction of the induced current is by using the _____.
Left-hand generator rule