Electromagnetism 1 & 2

Radi 121

electromagnet

coil or wire wrapped around an iron core that intensifies the magnetic field

solenoid

helical winding of current-carrying wire that produces a magnetic field along the axis of the helix

flux linkage

the interaction of one line of force and one loop of a conductor

permeability

defined as the ability of a material to attract the magnetic lines of force

faradays law

states that electric current cannot be induced in a circuit merely by the presence of a magnetic field, rather, the flux line must be changing

describe hans oersteds discovery

concluded any moving charge also produces a magnetic field

what did hans oersted discover

any moving particle generates a magnetic field

as the conducting wire is looped, the flux density of a solenoid

increases

when a ferromagnetic core is added, as with an electromagnet, the flux density is

increased

when a ferromagnetic core is added, as with an electromagnet, the magnetic field strength

increases

what are three ways in which the strength of the magnetic field lines in solenoids and electromagnets can be increased

1. increasing number of turns or loops

2. by increasing voltage of current flow

3. permeability of the core

where might we find electromagnets

1. detent locks in x-ray

2. circuit breakers and relays

3. slator electromagnets

another name for faradays law

first law of electromagnets

what law must the magnetic field (flux lines or lines of force) must be changing in order to induce electrical current

faradays law

list three ways to create motion between the lines of force and a conductor (wire) include

1. move the conductor through a stationary, unchanging strength magnetic field

2. move the magnetic lines of force through a stationary conductor with an unchanging conductor

3. vary the magnetic flux strength from a stationary magnet through a stationary conductor

what is the magnitude of the included EMF determined by

the number of the flux linkages per second

what happens to the flux density of a solenoid as the conducting wire is looped

increases

what happens when the electromagnet as a ferromagnetic core is introduced

1. enhance permeability

2. dipoles in same direction

3. increase magnetic field strength resulting in a stronger magnetic field.

can electric current be induced in a circuit merely by the presence of a magnetic field

no

what must the magnetic flux lines do in order to induce electrical current

changing

what happens when a conductor cuts across the magnetic flux or when a conductor is cut by a magnetic field

an electromotive force or potential difference is induced in the conductor

what are four factors influencing the magnitude of induced current

1. STRENGTH of magnetic field

2. VELOCITY of the magnetic field as it moves past the conductor

3. ANGLE of the conductor to the magnetic field

4. NUMBER OF TURNS in the conductor

describe strength of magnetic field

stronger magnetic field = greater the number of flux

describe velocity of the magnetic field as it moves past the conductor

faster the conductor is traveling = more flux linkages per second

describe angle of the conductor to the magnetic fields

closer to 90 degrees = more flux linkages per second

describe number of turns in the conductor

greater number of turns in conductor = more flux linkages per second; more EMF

stronger magnetic field =

greater the number of lines of flux

faster the conductor is traveling =

more flux linkages per second

closer to 90 degrees =

more flux linkages per second

greater number of turns in the conductor =

more flux linkages per second; more EMF

lens law

induced current flows in a direction such that it opposes action that induces it

what is lens law also known as

the second law of electromagnetic

right hand thumb rule… along a conductor

thumb: points w/ current flow

fingers: direction of magnetic field

right hand thumb rule… solenoid and electromagnetic

fingers = current

thumb = direction of north pole

right hand generator rule

index finger = magnetic lines of force

middle = current flow

thumb = movement of conductor on armature

left hand motor rule

index finger = magnetic lines of flux

middle finger = current flow

thumb = movement of conductor on rotor

list two items in x-ray circuitry that make use of faradays law

1. transformers

2. slator electromagnets

describe current flow verses electron flow in a circuit

current flow and electron flow are exact opposite of one another

electron flow means opposite of

current flow

when the question is talking about "generator" which hand should you use

right

when the question is talking about "motor" which hand should you use

left

is current a positive or negative

positive

is electron a positive or negative

negative

should you always start at the negative or the positive end

positive (current)

for finding north and south, which hand should you use

right

Where is the North Pole

Left

Label both the electron and current flow

- +

Where is the South Pole

Left

Label both the electron and current flow

- +

In a motor, what is the direction of the electron flow

Away from you

In a motor, what is the direction of electron flow

Away from you

In a generator, what is the direction of electron flow

Toward you

In a generator, what is the direction of the electron flow

Toward you

In a motor, what is the direction of the armature if the current is coming toward you

Up

In a motor, what is the direction of the armature if the current is going away from you

Up

In a generator, the direction of the current is

Toward you

In a motor, the direction of the electron flow is

Toward you

In a motor, the direction of the current is

Away from you

Which way is current flowing

- +

Where is the North Pole

Right

Where is the South Pole

left

If the magnetic field lines are flowing clockwise, what direction is the current flowing along a conductor

Away

If the magnetic field lines are flowing clockwise, what direction is the electrons flowing along a conductor

Toward