Module 5

Converting mechanical energy into electrical energy is the purpose of which device?

Generator

Moving a conductor by manual means within a magnetic field is the basic operation of a?

Generator

In which device does a commutator ring serve to feed current through an armature the same direction each time?

Motor

The rotor...

located in the middle of the stators, is made of an iron core surrounded by coils. The rotor itself does not touch the stators and it is not supplied with electric current.

A simple generator will produce what current type?

AC

Transformers operate best with?

AC

Magnetic resonance imaging equipment used for medical imaging operates with a magnetic field of...

0.5 up to 5 tesla (5 is experimental)

The following describes 4 diff coils. Which one, if moved through a magnetic field, would create the least voltage?

10 turns

If the number of coils of a conductor is 40 and the voltage is 110, what will the voltage be if the number of coils is increased to 80?

220

Magnetic Domain

A property of magnets in which the atoms in a small region are all aligned to produce a local magnetic field.

Dipole

A tiny magnetic field created by a single spinning electron.

As a variation of the right-hand rule, if the right-hand rule is to a coil carrying current with the fingers pointing in the direction of current flow, what will the thumb indicate?

Direction of magnetic field

What is the right-hand rule used to determine?

Direction of magnetic flux

A coil of wire is being moved through a magnetic field. If the speed with which it is moved is doubled, what happens to the resulting voltage?

Doubles also

What is the fundamental design difference between a generator and motor?

Electricity is applied to the armature of a motor

An iron bar wrapped with a wire carrying electric current is what class of magnet?

Electromagnet

The direction of the magnetic field lines around a wire carrying a current can be determined using what is called the right-hand rule...

If the thumb of your right hand points in the direction of the current flowing through a wire, your fingertips will point in the direction of the magnetic flux (field lines) around the wire.

Autotransformer

In this transformer, the wire is wound only once around the magnetic core; this winding functions as both the primary and secondary coils and operates on the principle of self-induction. The outside wires (taps) are attached at diff points along the coil on the secondary side, and the induced voltage varies depending on where the connections are made.

moving a bar magnet into a coil of wire will momentarily induce a current to flow through it...

Moving the magnet back and forth produces an alternating current.

The induction motor operates based on what principle?

Mutual induction

When a primary coil induces a current in a secondary coil, which of the following has occurred?

Mutual induction

There are 4 classifications of Matter

Nonmagnetic materials, Diamagnetic materials, Paramagnetic materials, and Ferromagnetic materials.

Which scientist used a compass and a wire carrying electric current to demonstrate and study electromagnetism?

Oersted

Electromagnetism

The movement of electrons in an electric current, which creates a magnetic field.

an electric current is considered a positive flow...

The negatively charged electrons are moving in the opposite direction to the current flow.

T or F: The commutator ring in a generator design briefly breaks contact between the armature and the circuit?

True

The magnetic field created by a current expands and collapses if the current is an...

alternating current

Electromagnetic

consists of an iron bar wrapped with a wire carrying electric current. This creates a temporary magnetic field by the flow of electricity and is only magnetic while electricity is flowing.

Any spinning electric charge (proton or electron) will...

induce a magnetic field.

All those tiny magnetic fields made of millions of individual electrons add up to make...

one bigger magnetic field.

The process of inducing magnetism in ferromagnetic material depends on...

the strength of the magnetic field in which the material is placed.

the inverse square law

the strength of the magnetic field is inversely proportional to the square of the distance.

Most atoms have equal numbers of opposing magnetic fields and...

they cancel each other out.

Most atoms are neutral because...

they have the same number of positive and negative charges.

Physical changes can...

weaken a magnet.

Nonmagnetic Materials

(i.e., glass, wood, plastic) are not affected by magnetic fields.

At what distance would you expect 2 magnets to have the strongest reaction to each other?

1/8 inch

What causes the armature to rotate in a simple motor?

2 magnetic fields trying to align

Step-down Transformer

A device included in the filament circuit to lower the voltage to the filament.

T or F: Lines of magnetic flux traveling in the same direction will attract each other?

False

T or F: Magnetic flux travels from north to south inside a magnet?

False

Transformers are named for their effect on...

voltage.

Magnetism is defined by its ability to attract...

Iron

Tesla

It is named for the American physicist Nikola Tesla.

Transformer

A device that operates on the principle of electromagnetic mutual induction to change the electric potential to a higher or lower voltage; also raises or lowers the current. Transformers are used in this purpose in x-ray equipment circuitry.

Solenoid

A device typically made by positioning an iron or steel core in the middle of a coil of wire; thereby increasing the strength of an electromagnetics magnetic field.

Artificial Permanent Magnet

A magnet that is manufactured. The manufacturing process turns an object into a magnet by inducing an alignment of atoms.

Conductor

A metal or other substance with electrons that are free to produce a current.

Direct-current Motor

A motor in which a commutator ring with rotating contacts or brushes reverses the currents direction in the coils as they rotate in the magnetic field of the permanent magnets. This ensures that the motor keeps turning in one direction.

Electric Motor

A motor in which current is supplied to create a magnetic field around the coils, which are moved by the magnetic field of the stronger permanent magnets surrounding the coil. This motion makes the motor turn.

Natural Magnet

A permanent magnet, known as a lodestone; a rock with a natural magnetic force acquired from the earth's magnetic field. A lodestone remains magnetic unless something happens to change its alignment of electrons.

A commutator ring in a generator design is attached to which of the following?

Armature

According to the laws of magnetism, how will the north pole of one magnet react to the south pole of another magnet if placed very close together?

Attract

In this type of transformer, there is only one winding of wire around the magnetic core (not to be confused with a shell type which has TWO windings). This winding is used as both the primary and secondary coil. The outside wires are attached at different points along the coil, and the induced voltage varies depending on where the connections are made.

Autotransformer

Which transformer design operates by self-induction?

Autotransformer

Which scientist formulated a law that explains a principle of electromagnetic induction?

Lenz

If this circle with a dot in the center represents a wire carrying electric current toward you, which of the following is true?

Magnetic flux lines flow counterclockwise

Basic transformer operation is based on what principle?

Mutual induction

Lodestones fall under what type of magnet?

Natural Magnets

The three basic types of magnets

Natural magnets, artificial permanent magnets, and electromagnet.

What is the unique electron characteristic of magnetic materials?

They all orbit in predominately one direction.

Autotransformers are important in x-ray equipment...

They supply voltages at different levels to the circuits in the x-ray machine.

T of F: The north and south ends of an electromagnet change each time an AC changes direction?

True

T or F: Depending on the application of the right-hand rule, the thumb can indicate either current flow or direction of the magnetic field?

True

What is the purpose of transformers?

to transform (increase or decrease) electric potential (voltage) or current. The change in voltage and current is an inverse relationship. As voltage is increased, current will decrease, and vice versa.

If we expose this iron bar to a strong magnetic field...

we cause the domains to align with this external field creating a magnet of the iron bar.

The stator...

is made of stationary electromagnets arranged in pairs around the rotor.

Cobalt and nickel

refer to these elements in their pure form

The two most common types of transformers are...

the closed-core transformer and the shell transformer.

the more coils cut by the magnetic field...

the greater the induced voltage.

The induction of a "back" current within the same coil is called?

Self-induction

The external magnets of an induction motor are called?

Stators

What are the 2 major parts of the induction motor?

The stator and the rotor.

The physical motion of tapping the material will help jar the atoms into...

alignment when in a magnetic field.

Who discovered that moving a conductor, such as a wire, through a magnetic field induces a current to flow in to that wire. This is called electromagnetic induction...

the British scientist, Michael Faraday

Ferromagnetic Materials

(i.e., iron, cobalt, nickel) are those strongly attracted to magnets.

Paramagnetic Materials

(i.e., platinum, gadolinium, aluminum) are those weakly attracted to magnetic fields.

Diamagnetic Materials

(i.e., water, mercury, gold) are weakly repelled by magnetic fields.

The average magnetic field strength of the earth is about...

5 X 10-5 T (0.00005 T)

similarities and differences between the principles of both magnetic fields and electric fields

A 2nd principle is that all magnets have both a north and a south pole. This property is different from electric fields, in which a positive or negative electrical charge can exist by itself.

Armature

A coil of wire that rotates inside a magnetic field to produce an electric current. The more turns of wire in the coil, the higher the voltage induced in the wire.

Electromagnetic Induction

A current that is induced to flow in a wire by moving the wire through a magnetic field or by moving a magnetic field through the wire, or by varying the strength of the magnetic field.

Step-up Transformer

A device in the primary circuit that raises voltage to the kilovolt level needed to power the x-ray tube. A very high voltage is needed to produce x-rays. The primary coil is in the primary circuit, the secondary coil in the secondary circuit.

Autotransformer

A device that raises or lowers voltage in the primary circuit, depending on the setting chosen on the machines control panel for the kilovolt peak voltage (kVp).

Electric Generator

A generator that produces an electric current by rotating loops of wire through a fixed magnetic field.

Polarity

A term referring to the north and south poles of a magnetic field.

Closed-core Transformer

A type of transformer in which the coils are wound around a square or circular core to provide a continuous path for the magnetic field; it is insulated to help contain and direct the magnetic force lines.

Iron

A very common element used for magnets and utilized in magnetic fields.

Lodestones

Are thought to have gained their magnetism from the earth's magnetic field. The ancient Greeks first found such magnetic rocks in a region then called Magnesia, for which magnets are named. They are permanent magnets in that, unless something happens to change their arrangement of electrons, they will remain magnetic.

Water is magnetically classified as which of the following?

Diamagnetic

Nickel

Does not exhibit strong magnetic properties bc it only contains 25% nickel and the rest is copper.

Increasing the strength of the magnetic field will also proportionately increase the voltage...

Ex: doubling the strength of the magnet will double the induced voltage.

Increasing the coil's speed of motion through the magnetic field also increases the voltage.

Ex: moving the magnet twice as fast will double the induced voltage.

Artificial Permanent Magnet

In this process, a nonmagnetized magnetic material is exposed to a strong magnetic field. This field pushes and pulls the atoms into alignment through the forces of attraction and repulsion.

the voltage induced in a wire also depends on the angle of the motion between the wire and the magnetic field...

Motion of the wire perpendicular to the magnetic field produces more voltage than the motion at an oblique angle bc perpendicular motion cuts through more lines of magnetic force per unit of time.

The magnetic poles are like the top and bottom of a magnet...

No matter how many pieces you cut the magnet into, each piece still has a top and bottom. Each still has a north and a south pole because of the alignment of the atoms. Electric fields do not have this characteristic.

Who is credited with establishing the principle of electromagnetism?

Oersted

Platinum is magnetically classified as which of the following?

Paramagnetic

Like poles of a magnet or charges of electric fields will?

Repel

Like poles of magnets or charges of an electric fields will...

Repel

laws of magnetism

The 1st law is that every magnet, even if it is only one charged particle (proton or electron), has a north and a south pole. The 2nd law is that like poles repel each other and unlike poles attract each other. The 3rd law is the force of attraction (or repulsion) varies directly as the strength of the poles and inversely as the square of the distance between them.

Who established the principle of electromagnetism when he discovered that a compass needle is deflected to a wire that carries a current. When the current is turned off, as expected, the needle then points north to the earth's magnetic pole.

The Dutch physicist, Hans Oersted.

Magnetism

The ability of certain materials to attract iron, cobalt, or nickel.

Magnetic fields always reach from north to south outside the magnet...

The field of a positive charge points out from the charge and the field of a negative charge points into the charge. Again, this is different from electrical charges.

Lenz's Law

The principle that an induced current flows in the opposite direction of the magnetic field change that induced it.

Self-induction

The process that occurs in a single coil of wire when an alternating current flows through it; the flow of electrons in one direction produces a magnetic field that induces a second current to flow in the wire, but in the opposite direction.

T or F: A stronger magnetic field will magnetize a ferromagnetic material more strongly?

True

T or F: Rubbing a ferromagnetic material against a permanent magnet will magnetize that material?

True

When all of the magnetic domains are caused to align, they create...

a magnet. Iron is a good example of this.

Atoms of iron...

have electrons that spin predominately in one direction.

Rubbing the ferromagnetic material against a permanent magnet will...

help bring the atoms into alignment.

increasing the number of coils of wire increases magnetic field strength...

increasing the number of coils in a moving magnetic field proportionately increases the voltage induced in the coils.

A stronger field will magnetize the material more strongly...

it will pull more domains into alignment.

A magnetic field consists of...

lines of force in space called flux.

An iron bar will have...

many magnetic domains.

Alignment

that the spin of the electrons in the atoms is predominantly in the same direction.

In magnetized iron...

the atoms line up in a set way so that all the free electrons spin in the same direction.

In magnetic materials...

the orbital electrons of its atoms spin in predominately one direction.

Heating a magnet or dropping it can knock some of the atoms out of alignment which will...

weaken the magnetic field.

The following describes 4 different coils. Which one, if moved through a magnetic field, would create the greatest voltage?

40 turns (loops)

Magnetic fields have three general characteristics.

1st, the lines of force travel from the south pole to the north pole INSIDE the magnet & from the north pole to the south pole as curved lines in space OUTSIDE the magnet. 2nd, lines of force in the same direction repel each other, and lines of force in opposing directions attract each other. 3rd, magnetic fields are distorted by magnetic materials & unaffected by nonmagnetic materials.

Induction Motor

An AC motor consisting of a rotor and stator. The electromagnets in the stator have a changing magnetic field that causes the rotor within to turn.

Electromagnet

An object that creates a temporary magnetic field through the flow of electricity. It has many applications in electric equipment.

Natural magnets

Are found in the earth and called lodestones. Lodestones are a large piece of magnetite, which is an iron ore.

similarities and differences between the principles of both magnetic fields and electric fields

The 1st principle is that like poles (or charges) repel and unlike poles (or charges) attract. This is true of both types of fields.

Tesla

The SI unit (abbreviated as T) used to measure the strength of a magnetic field. (1 Tesla = 10,000 Gauss)

Magnetic Field

The area around moving charged particles. It exerts a magnetic force on certain kinds of particles within the field.

The inverse square law applies to both electric and magnetic fields.

The force of one pole on another is directly proportional to the product of the magnetic strength of each pole divided by the square of the distance between them. The same is true of electric fields where the intensity diminishes by the square of the distance.

Shell Transformer

The most commonly used transformer; it "traps" the magnetic forces more efficiently in order to induce the strongest possible current in the secondary coil.

Mutual Induction

The phenomenon in which a current in one conductor induces a current to flow in another conductor.