Exposures 1 CH 4
An iron bar exposed to a strong magnetic field may become what?
Artificial permanent (An artificial permanent magnet can be created when a ferromagnetic material such as iron is placed in a strong magnetic field. )
What aligns to form magnetic domains?
Atoms (The atoms of magnetic materials are "atomic magnets" or dipoles and, when aligned, form magnetic domains.)
(T/F) A magnet is formed when all of its "atomic magnets" align.
True (A magnetic material can exist in a non-magnetic state when its domains are not aligned. But when they are aligned, the result is the creation of a magnet. )
(T/F) Heating a magnetized iron bar will cause it to lose some or all of its magnetism.
True (Heating a magnetized material allows the domains to move about more freely and causes the magnet to lose its magnetism)
(T/F) With electric fields, positive and negative charges exist separately.
True (One difference between electric and magnetic fields is that electric charges (unlike poles) can exist separately. Objective: Compare and contrast magnetic and electric fields.)
(T/F) The inverse square law applies to both electric and magnetic fields.
True (One of the common characteristics of both electric and magnetic fields is that they both vary inversely as the square of the distance (inverse square law). )
(T/F) Tapping an iron bar against a solid object in a magnetic field will help magnetize that material.
True (Tapping a magnetic material in a magnetic field actually jars some of the domains into alignment.)
According to the laws of magnetism, how many poles will an atomic magnet have?
Two poles at this level (According to the laws of magnetism, no matter what the level, all magnets have two poles. Objective: Explain the laws of magnetism.)
earth has a ____ magnetic field
Very small
Right hand thumb rule for electromagnetism: thumb indicates direction of: fingers indicate direction of:
current magnetic field lines (if the thumb points in the direction of actual electron flow, then a left-hand thumb rule must be used to show the direction of the magnetic field lines of force.)
what can generate a magnetic field?
electrical current
the flux density can be increased further still by adding a ferromagnetic core, this configuration is called:
electromagnet
temporary magnets produced by moving currents
electromagnets
what are used as remote control devises in a circuit breaker, and in temporary locks
electromagnets
Root mean square (rms) values of the total voltage and amperage in an alternating current are _____ (different or equivalent) to the effect that would be produced in a direct-current resistance by the same factors.
equivalent.
Simply magnetic; materials such as iron, cobalt, and nickel are highly permeable and greatly susceptible to induction.
ferromagnetic.
both Solenoids and electromagnets demonstrate magnetic properties only while electric current is:
flowing.
the stronger magnetic field, the greater # of flux lines:
flux density
the motor principle is also used in meters:
galvanometers for direct current, when permanent magnets are used, to indicate current. dynamometers for alternating current, when electromagnets are used. being phased out by digital meters, which provide numerical indications of current.
fleming's right-hand ___ rule (motor, solenoid, generator) states that if the thumb points in the direction the conductor (or armature) is moving and the index finger points in the direction of the magnetic lines of force field, then the middle finger will indicate the direction of the current
generator
device that converts mechanical energy to electrical energy using faraday's discovery of moving lines of flux in relationship to a conductor to induce current
generator-converts mechanical energy to electrical energy
When current supply reverses, the north and south poles will induce an opposing potential difference, attempting to induce against the incoming supply of electrons. this tendency of an alternating current is called:
inductive reactance. measured in ohms of resistance
force between two magnetic fields directly proportional to product of their magnitudes & inversely proportional to *square* of distance between them.
inverse square law
How are permeability and retentivity related?
inversly
what are the components of force fields?
lines of force lines of flux magnetic field
atoms with electrons in magnetic moment in the same direction creates magnetic field:
magnetic dipoles
Groups of atoms that exhibit a net magnetic field in a distinct direction are known as:
magnetic dipoles or magnetic domains
what happens when a non magnetized iron bar is brought into a external magnetic field? (the dipoles of the iron bar align themselves with the lines of force)
magnetic induction
regions of magnetism always exist as dipole. no matter how small it gets. what are these regions called?
magnetic poles
Charged particle in motion, magnetic field perpendicular to the motion
magnetism
Inverse square law applies to?
magnetism electric field gravity.
continuing this switching of current flow results in the conductor continually being simultaneously repelled and attracted in a circle, thus turning a shaft and supplying the ____ motion
mechanical
fleming's right-hand ____ rule (generator, motor, solenoid) states that if the index finger points in the direction of the magnetic lines of force field and the middle finger points in the direction of the conventional current (left hand if electron flow), the thumb will indicate the direction the conductor will move
motor
a device that is supplied with electrical current to produce mechanical motion is called a:
motor. operate on the same principles as generators, but in reverse.
Iron oxide in the ground for long periods of time, dipoles orient in the same direction
natural (iodestones) or earth's crust
the right-hand rule for solenoids the thumb will indicate: the fingers will indicate:
north pole direction of the current
In the case of the negatively charge electrons orbiting the nucleus of an atom, the closed look of the orbit cancels all but the field that is perpendicular to the plane of the motion. This perpendicular magnetic force is called:
orbital magnetic moment
When a charged particle is in motion, a magnetic force field is _____ to the motion that will be created
perpendicular
the coil supplied with a current is called? where as the coil in which the current is induced is called? This describes?
primary coil secondary coil mutual induction
what are the laws of magnification?
repulsion & attraction inverse square law magnetic poles
alternating current is produced when the wire's motion relative to the lines of force is:
reversed
when the current flow is switched by the commutator ring, the magnetic lines of force are ___
reversed
instead of supplying current to the coil in the magnetic field, an induction motor uses a device called a:
rotor consist of bars of copper around an iron core.
the frequency (Hz) of the sine wave is determined by the number of cycles per ____.
second. 1 cps= 1 Hz
when the flow of current supply reverses, the previously established electromagnetic north and south poles will induce an opposing potential difference. (induces the incoming supply of electrons)
self-induction
alternating-current motors use what type of rings
slip rings
what permits the circuit to remain stationary while the armature rotates without breaking the electrical contact between them
slip rings and brushes. each slip ring connects to one end of the armature wire.
If a series of loops are made, creating a coil, the flux density is greatly increased. when current is flowing through this type of coil it is called:
solenoid
these are often used as detent locks on the overhead crane of x-ray tubes
solenoids
a magnetic effect is also established by electrons, the effect created by the movement of electrons moving on their axis is called:
spin magnetic moment
consist of pairs of stationary magnets (or, more commonly electromagnets) arranged around the rotor
stator. the stator must be supplied with multiphase current. the stator electromagnets are energized in sequence
What are the four Faraday laws?
the *strength* of the magnetic field. The *speed* of the motion between lines of force and the conductor The *angle* between the magnetic lines of force and the conductor. The *number of turns* in the conducting coil.
unit of charge potential difference current magnetism
unit of charge- coulomb potential difference- volt current- amp magnetism- tesla
when connected in parallel, it measures potential difference in volts, and is called a:
voltmeter
Direct-current motors use ____ rings
commutator
a single ring that is divided in half, which each half connected to one end of the armature wire
commutator
a direct-current generator uses ___ rings:
commutator rings
what are the 3 ways to induce a electrical current?
*Move the conductor* through a stationary unchanging-strength magnetic field *Move magnetic lines of force* through a stationary conductor with an unchanging strength magnetic field *Vary the magnetic flux strength* from a stationary magnet through a stationary conductor. As the flux strength varies, the lines of force will expand and contract, in effect causing the relative motion necessary *to induce current*
The basic premise of electromagnetic induction is that which of the following move?
1. Magnetic field 2. Conductor (The general principle of electromagnetic induction is that either the magnetic field fluctuates (moves) or the conductor moves. Either of these things will result in a conductor being "cut" by a magnetic field, thus inducing a current.)
commutator rings are required, in order to switch the flow of current when the conducting coil begins to reach a _____ degree postion
180 degree where the lines of force no longer attract or repel one another
The following are four different magnetic fields. If the same coil of wire is passed through each, which will result in the greatest induced voltage? 1T, 1.5, or 2.5T
2.5 T (The strength of the magnetic field is one factor that determines the voltage induced. The stronger the magnetic field, the greater the induced voltage.)
Which of the following conductor angles, in relation to the magnetic field, will produce the greatest voltage?
90 degree angle to the field (The angular relation of the conductor to the field is another factor that determines the voltage induced. The greater the angle, up to 90 degrees (perpendicular), the greater the induced voltage because more coils will pass through the magnetic field per unit time.)
Materials such as beryllium, bismuth, and lead are weakly repelled by all magnetic fields.
Diamagnetic
the factors that govern the effectiveness of Solenoids and electromagnets are the ____of the coil, its ____, and the current passing along the coil
Diameter, length
when conducting wire is looped (U-shaped), that the inside of the loop the magnetic fields from both sides join to _____ the magnetic flux density
Double.
Which type of magnet has many applications in electrical equipment?
Electromagnet (Electromagnets, because they can be turned on and off, have many applications in electrical equipment, and you will see them used in x-ray equipment)
(T/F) Magnetic poles can exist separately from each other and may have only one pole.
False (No matter how small the magnet, it will always have two poles. )
What (law) states that four factors regulate the strength of induced current when magnetic lines of force and a conductor are in motion relative to one another?
Faraday's law
what law makes it possible to determine the direction in which the induced current will flow?
Faradays
Materials strongly attracted to magnets are classified as which of the following?
Ferromagnetic (Those materials that are strongly attracted to magnets are classified as ferromagnetic.)
who first discovered the relation ship between a electrical field and magnets, what year?
Hans Oersted, 1820
This permits a revised version of Ohm's law to be applied for alternating current:
I=V/Z Where I= rms amperage V= rms voltage Z= impedance
what type of motors are used in rotating anode x-ray tubes ,where the target anode is attached to the induction motor rotor inside the glass vacuum tube.
Induction. because magnetic lines of force will pass through glass and a vacuum, the electromagnets can be positioned outside the vacuum tube, thus avoiding interference with the high voltages required to produce x-rays.
Why is AC desirable for mutual induction?
It creates a moving magnetic field. (To have electromagnetic induction we must have either the conductor or the magnetic field move. With AC, a different magnetic field is created each time the current changes direction; this, in effect, creates a moving magnetic field.)
If a magnetic material is placed in the field of a magnet, what happens to that field?
It is distorted. (One of the characteristics of magnetic fields is that they are distorted by magnetic materials. Objective: Discuss the nature of a magnet.)
what law states that induced current flow sets up a magnetic field opposing the action that produced the original current or, simply, that induced current opposes any flux change.
Lenz's Law
Any moving charge produces a:
Magnetic field
If this circle with an "X" in the center represents a wire carrying current away from you, which of the following is true? Magnetic flux lines flow clockwise or counterclockwise.
Magnetic flux lines flow clockwise. (Using the right-hand rule and pointing your thumb away from you, you will see that the flux lines flow clockwise)
An induced magnetic field trying to align with an external magnetic field is the basic principle of operation of which device?
Motor (In an induction motor, the stators (electromagnets) "fire" in opposing pairs and in sequence around a rotor. This induces a current and magnetic field in the rotor. This induced field then attempts to align with the ever changing external field causing the rotor to turn.)
What are the three ways to create the motion between lines of force and a conductor?
Move the conductor, move magnetic lines of force, vary the magnetic flux
Materials such as wood, rubber, and plastic are not affected by magnetic fields and can not be magnetized.
Nonmagnetic
Which scientist conducted experiments demonstrating that a magnetic field created by a flow of electric current was greater than the earth's magnetic field?
Oersted (While all of the scientists listed should be familiar to you for their roles in the physics we study, it was the Dutch physicist Hans Oersted whose experiment demonstrated the nature of this field.)
Materials such as platinum and aluminum, have low permeability and weak attraction to magnetic fields.
Paramagnetic
Gadolinium is useful in MRI because it has which magnetic property?
Paramagnetic (Gadolinium is weakly attracted to magnets, and it is the property that makes it useful as a contrast agent in MRI)
The ease with which a material can be magnetized
Permeability
The ability for a material to remain magnetized.
Retentivity
Magnetism SI unit is: Flux density is measured in: Earth's magnetic field is:
SI unit is: weber (wb) = 10^8 lines of flux Flux density is measured in: tesla and gauss 1 T= 10,000 G = 1 wb/m^2 Earth's magnetic field is: 0.0001 T or 1 G
The type of curve produced by an AC generator.
Sine wave
What piece of the simple generator provides a means for conducting electricity out of the loop?
Slip rings (Because the armature is rotating we need a means of "mobile" contact with the circuit. The slip ring is attached to the armature and slides against brushes attached to the circuit. This creates the moving contact we need to conduct electricity out of the generator.)
The strengths of _____ and _____ is determined by the number of loops (or turns) of wire, the current strength, and the permeability of the core.
Solenoids and electromagnets.
What is the advantage of configuring a wire carrying electric current into a coil (solenoid)?
Strengthens the magnetic field (By coiling the wire, the magnetic flux lines are concentrated and overlap in the center, and the magnetic field is strengthened.)
what type of alternating-current motor have conducting coils that turn at the same speed as the generator armature supplying the current
Synchronous alternating current motors
there are two major types of alternating-current motors
Synchronous alternating current motors Alternating-current induction motors
T/F electromagnetic relays are similar to circuit breakers
T
What atomic characteristic of a magnetic material creates a dipole?
Their electrons spin predominately in one direction. (When atoms have electrons that orbit or spin in predominately one direction, the net effect is an atomic magnet called a dipole.)
Increasing voltage and decreasing current through mutual induction is the function of which of the following?
Transformer (The function of the transformer is to increase or decrease voltage and current. This is done through electromagnetic mutual induction. )
The *south poles* of two magnets are placed 1 millimeter from each other. Which of the following describes the reaction?
Very strong repulsion ( According to the laws of magnetism, like poles repel and unlike poles attract. Further, the strength of attraction or repulsion is inversely proportion to the square of the distance. So the closer these two poles are, the stronger the repulsion.)
apparent total resistance of an alternating current is called impedance, which is represented by what symbol:
Z
the flow occurs in the secondary coil because the primary coil does what?
alternates. this follows the rule that moving lines of force from a varying-intensity current will induce electron flow in a wire.
what type of alternating-current motor utilizes a rotor coil with the exterior magnetic field supplied by several pairs of electromagnets, producing a strong magnetic field, increasing the power of the motor, and permits it to run at a desired speed
alternating-current induction motors
when a meter is connected in series, it measures current in amperes and is called an:
ammeter.
the rotating coil or coils of a dynamo or electric motor.
armature
when heated, has strong magnetic field
artificial permanent (alnico) Ex: Blacksmith