The Nature of Magnetism Flashcards by Colette Raina Sendaydiego

The phenomenon of magnetism was discovered by the _____ about _______.

Chinese, 2637 B.C.

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The magnets used in the primitive compasses were called ________ or _______.

lodestones, leading stones

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What are the crude pieces of iron ore called lodestones?

magnetite

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Lodestones are classified as what type of magnets?

natural magnets

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What is the only other natural magnet aside from lodestones?

the earth itself

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What are all other magnets made by humans known as?

artificial magnets

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These are those materials which are attracted or repelled by a magnet and which can be magnetized themselves.

magnetic materials

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most common magnetic materials

iron and steel

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those of hard magnetic materials that retain their magnetism when the magnetizing field is removed

permanent magnets

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one that has no ability to retain a magnetized state when the magnetizing field is removed

temporary magnet

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Classifications of Magnetic Materials based on applications

Ferromagnetic materials, Paramagnetic materials, Diamagnetic materials

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Classifications of Magnetic Materials based on strong magnetic properties of iron

magnetic, nonmagnetic

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includes iron, steel, nickel, cobalt, and commercial alloys

ferromagnetic materials

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nonmagnetic materials that have ferromagnetic properties of iron

ferrites

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A common application of a ferrite is a ferrite core in the coils for __________.

RF (radio-frequency) transformers

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range of permeability of ferrites

50 to 3000

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includes aluminum, platinum, manganese, and chromium

paramagnetic materials

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relative permeability of paramagnetic materials

slightly more than 1

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includes bismuth, antimony, copper, zinc, mercury, gold, and silver

diamagnetic materials

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relative permeability of diamagnetic materials

less than 1

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two points of a magnet opposite each other

north pole, south pole

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force that exists arounds the magnet invisible to the naked eye

magnetic field

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the ______ the magnet, the greater the number of lines of force and the ________ the area covered by the filed

stronger, larger

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What does the direction of the lines outside the magnet shows?

path a north pole would follow in the field

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What do you call an entire group of magnetic field lines which flow outward from the north pole of a magnet?

magnetic flux

What is the symbol for magnetic flux?

Greek lowercase letter phi

What is the SI unit of magnetic flux?

weber (Wb)

1 Weber = n magnetic field lines n = ?

1 x 10^8

What is the symbol for magnetic flux density?

What is one weber per square meter called?

tesla

It is the magnetic flux per unit area of a section perpendicular to the direction of flux.

Magnetic Flux Density

SI unit of magnetic flux density

tesla (T)

When was the relation between magnetism and electric current discovered?

1819

Who discovered that an electric current flowing through a conductor produced a magnetic field around that conductor?

Danish scientist Oersted

A _____ current will produce many lines of force extending far from the wire, while a _____ current will produce only a few lines close to the wire.

high, low

Every section of the wire has the field of force around it in a plane _______ to the wire.

perpendicular

What is a convenient way to determine the relationship between the flow of current in a conductor and the direction of the magnetic lines of force around the conductor?

right-hand rule

two results of bending a straight conductor into the form of a single loop

magnetic fields are denser inside the loop, all lines inside the loop are aiding in the same direction

When is a coil of wire conductor formed?

more than one loop or turn

What is the symbol for magnetomotive force?

SI unit for magnetomotive force

ampere-turns (At)

The _____ of a magnetic field in a coil of wire depends on how much current flows in the turns of the coil.

strength

The more current, the ______ the magnetic field.

stronger

The more turns, the more ______ are the lines of force.

concentrated

the product of the current times the number of turns of the coil

magnetomotive force

formula of magnetomotive force

F = NI

formula of magnetic flux density

B = Φ/A

concentration of lines of forces; depends on how long the coil is

magnetic field intensity

If a coil with a certain number of ampere-turns is stretched out to twice its original length, the intensity of the magnetic field will be ________.

half as great

symbol of magnetic field intensity

formula of magnetic field intensity

H = F/l

also known as BH curve

flux-field curve

used to show how much flux density results from increasing the amount of field intensty

flux-field curve

it is the ratio of flux density to field intensity

permeability

unit of permeability

Tm/At

The average value of permeability is measured at the point where the ______ is first established

knee

permeability of air

4π x 10^-7 Tm/At

What is the opposition to the production of flux in a material called?

reluctance

symbol for reluctance

it is inversely proportional to permeability

reluctance

iron has high permeability and therefore ____ reluctance

low

air has ______ permeability and hence has high reluctance

low

formula of reluctance

R = l/µA

states that if a conductor "cut across" lines of magnetic force, or if lines of force cut across a conductor, an emf or voltage is induced across the ends of the conductor

Principle of Electromagnetic Induction

When was the principle of electromagnetic conduction discovered and who discovered it?

1831, Michael Faraday

The most important application of relative motion between conductor and magnetic field is made in _________.

electric generators

In a DC generator, how are fixed electromagnets arranged?

in a cylindrical housing

Since the conductors are in series in the coil, the induced voltages add together to produce the _______ of the generator.

output voltage

According to ________, the value of the induced voltage depends upon the number of turns of a coil and how fast the conductor cuts across the lines of force or flux.

Faraday's Law

states that an induced voltage always has such a direction as to oppose the change in magnetic flux that produced it

Lenz's Law

Three Factors determining Induced Voltage

amount of flux, number of turns, time rate of cutting

The more the lines of force that cut across the conductor, the _____ the value of induced voltage.

higher

The more turns in a coil, the ______ the induced voltage.

higher

The faster the flux cuts a conductor, or the conductor cuts the flux, the _______ the induced voltage because ______ lines of force cut the conductor within a given period of time.

higher, more

Formula for Faraday's Law and Lenz's Law

ε = N(ΔΦ/Δt)