chapter 9

An ideal transformer has 50 turns in the primary and 500 turns in the secondary. An input of 12 V will produce an output of

120 V (500/50 *12)

The voltage across the input terminals of a transformer is 110 V. The primary coil has 50 loops and the secondary coil has 100 loops. The output is

220 ( 110 * (100/50)

An electronic game requires 6 V for operation. A transformer allows it to be powered from a 120-V outlet. If the primary has 500 turns, the secondary has

25 turns

A current of 4 A exist in the primary coil of a transformer. The voltage across the primary coil is 110 V. What is the power output of the secondary coil?

440 W (110*4)

A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in the secondary coil is

5 A

Magnet A has twice the magnetic field strength of magnet B, and at a certain distance it pulls on magnet B with a force of 50 N. With how much force does magnet B then pull on magnet A?

50 N

The voltage across the input terminals of a transformer is 110 V. The primary coil has 50 loops and the secondary has 25 loops. The output is

55 V ( 110 / (50/25) )

A transformer has an input of 6 V and an output of 42 V. If the input is changed to 12 V, the output would be

84 V

When a current-carrying wire is placed in a strong magnetic field, no force acts on the wire. What orientation of the wire is likely?

Maximum force occurs when the wire is at 90 degrees to the field.

Break a bar magnet in half and each half is

a complete magnet

A galvanometer calibrated to read potential difference is

a voltmeter

When the current in a wire is reversed, the direction of the surrounding magnetic field

also reverses

A transformer requires

alternating voltage

A galvanometer calibrated to read current is

an ammeter

Moving electric charges will interact with

an electric field and a magnetic field

Surrounding every moving electron is

an electric field and a magnetic field

Like kinds of magnetic poles repel while unlike kinds of magnetic poles

attract

Compared with the current in the primary coil of a transformer, the current in the secondary coil

can be greater or less

An electric generator of itself

cannot produce energy, but convert energy of other forms to electric energy

A magnetic force acts most strongly on a current carrying wire when it

carries a very large current or is perpendicular to magnetic field

Transformers use ac so there will be the required

change in magnetic field for operation

Voltage can be induced in a wire by

changing the current in nearby wire, moving the wire near a magnet, and moving a magnet near the wire

The rule for the interaction of magnetic poles is similar to the rule for electric

charges

Magnetic field lines about a current-carrying wire

circle the wire in closed loops

The magnetic field lines about a current-carrying wire form

circles

Electromagnetic induction is employed in

credit cards, ipads, and computers

The magnetic field inside a current-carrying coil increases when

current is increased and the number of loops of wire in the coil increases

An electromagnet consists of a

current-carrying a coil with a piece of iron inside

Earth's magnetic field affects cosmic rays by

deflecting them

Since magnetic force is always perpendicular to moving charges, magnetic force can only change an electron's

direction

Maxwell's counterpart to Faraday's law simply states that

each change in field induces the other

A galvanometer measures

electric current

The rapid alteration of a magnetic field induces

electric field

Which force field can increase a moving electron's speed?

electric field

Faraday's law is the law that describes

electromagnetic induction

When a change of magnetic field occurs in a closed loop of wire,

electromagnetic induction occurs, a voltage is induced in the wire, and a current is made to flow in the loop of wire

What field generation cannot create is

energy

A transformer actually transforms

energy from one value of voltage to another

Power is the rate at which

energy is transferred

Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is

equally huge

Magnet A has twice the magnetic field strength of magnet B and pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is

exactly 100 N

Superconducting electromagnets

exist now

The metal detectors that travelers walk through at airports operate via

faraday's law

The frequency of a generated electromagnetic wave matches the

frequency of vibrating charges

A device that transforms mechanical energy to electrical energy is a

generator

Alternating current is normally produced by a

generator

Compared with the voltage input to a transformer, the voltage output can be

greater or less

Refrigerator magnets

have short range

A magnetic field easily penetrates

human flesh and plastic coatings

The main difference between a generator and a motor involves which terminal is

input and output

Magnetic domains normally occur in

iron

The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a

iron rod

Unlike electric charges, magnetic poles cannot be

isolated

A superconducting electromagnet makes use of

low-resistance coils of wire

The rapid alteration of an electric field induces

magnetic field

Electromagnetic induction occurs in a coil when there is a change in

magnetic field intensity in the coil

Surrounding our planet Earth are

magnetic fields and cosmic rays

A bar magnet that holds a chain of nails illustrates

magnetic induction

A galvanometer is a useful device in electric

meters

Electromagnetic induction was discovered by

michael faraday and joseph henry

A device that transforms electrical energy to mechanical energy is a

motor

Magnetism is due to the motion of electrons as they

move around the nucleus and spin on their axes

The source of all magnetism is

moving electric charge

An iron nail is more strongly attracted to the

north or south pole- no difference

Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a

north pole

If the primary of a transformer were connected to a dc power source, the transformer would have a voltage output

only briefly while being connected or disconnected

When a current-carrying wire in a magnetic field experiences no force it is likely

parallel to the field lines

The minimum magnetic force on a moving electron occurs for motion

parallel to the magnetic field

Maximum magnetic force occurs when electrons move

perpendicular to the magnetic field direction

The intensity of cosmic rays bombarding the Earth's surface is largest at the

poles

The rate at which a transformer transfers energy is called

power

When a magnet is thrust into a coil of wire, the coil tends to

repel the magnet as it enters

The energy source for a generator may be

steam from a turbine, wind, or a waterfall

A topic that most underlies electrical studies and all of physics is

the conservation of energy

Voltage produced by a generator alternates because

the magnetic field that produces it alternates

An iron rod becomes magnetic when

the net spins of its electrons are in the same direction

An electric motor and electric generator differ in

the roles of input and output

When a bar magnet is broken in half, the magnetic strength of each piece is

the same

compared with the power input to an ideal transformer, the power output is

the same

When a magnet is thrust into a coil that has twice the number of loops, the induced voltage is

twice as much

Every magnet contains at least

two poles

An electric motor and electric generator are

very similar devices

A step-down transformer decreases

voltage

Changing the magnetic field intensity in a closed loop of wires induces

voltage and current

The frequency with which a magnet plunges into and out of a magnetic field equals the frequency of the induced

voltage and current

Thrust a magnet into a coil of wire and you'll induce

voltage and current

When a magnet is thrust into a coil of wire, a greater voltage is induced

with faster thrusting motion and with a greater number of loops in the coils

A magnetic field exists in a current-carrying coil of wire

with or without a contained piece of iron

We know that a compass points northward because Earth is a giant magnet. Does the northward-pointing needle point northward when the compass is brought to the Southern Hemisphere?

yes