Draw the magnetic field between two opposite poles.

How will the north pole of a compass point if placed at points A-D? What dir. is the B-field at A-D?How would the picture change if N became S and v.v.?

B

C

N SA>

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>

>

D

Draw the magnetic field between two N poles.

How will the north pole of a compass point if placed at points A-D? What dir. is the B-field at A-D?

How would the drawing change if it were two S poles?

A

B

C

N N>>

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> D

NSq

B: __________ __________

A: a wire________ w/ current

magnet

C: wire with________________________

The charges in ____________________ experience

a _________________ force Fmag.

vv

force on a magnet

force on a moving charge

at restmovingcharge

no currentbut moving

all 3 cases

magnetic

q

III. Electromagnetic Induction.

Oersted: Moving charge (I) exerts a _____________________.

N’s 3rd law: A magnet exerts a __________________________ .

Magnitude (strength) of Fmag:

Fmag = ________________, is angle between v and B.

Notice: If = 0, then Fmag = _______ .

Direction of Fmag.

Fmag is _______________________ to v and B.

z

x

y

For any charge q moving with a velocity v through a B:

qvB sin

perpendicular

0

Ex: A charged particle moves at different angles to B. Assume v is the direction of the charge's motion.

v

BFmag

z

x

y

v

BFmag

z

x

yv

B

= _____ = _____ = _____

Fmag = _______ Fmag = _______ Fmag = _______

900 450 00

max. med. min.

Fmag=0

Ex: The force between 2 current-carrying wires is used

to define the ________________:

1 ______________ = the amount of current in two infinite

wires of negligible diameter separated by a distance

of _________________ that will produce a magnetic force of

_______________________ per meter of length.

Note: The force is ___________________ when the current

is in same direction in both wires.

>

>

Fmag

FmagI

Iwire 1

wire 2

ampere

ampere

1 meter

2 x 10-7 N

attractive

Electromagnetic Induction:“______________ motion between a conductor and a B fieldinduces (creates) a ___________________ in the conductor.”

Case C (again): A wire conductor moved in a B field or __________________________________

NS

Fmag causes the ______________________________________This ___________________________ an electric field in the wire, which results in an _______________________________or _________________________between the ends of the wire.

the magnet could be moved

electrons to move to one end of the wire.induces (or sets up)

induced potential difference,induced voltage

potential differenceRelative

E

N S

Ex 1. A wire moved between two magnets. Its velocity v is perpendicular to B: = ______

v

v

The wire "cuts" _____________________ the most B lines

The angle between v and B is _______ , so Fmag is ________.

____________ potential difference V is induced in the wire.

In symbols: v B

Because the strength of the _________________ depends on the angle between the __________________ and the B field,the amount of induced ______________________ also does.

magnetic forcev of the chargepotential difference

900

directly through

Maximum

max. V

900 max.

N S

Ex 2. A wire moved at an angle: < <

v

v

The wire cuts ________________B field lines.

Because the angle between v and B is ____________

Fmag is ____________________

_______ V is induced in the wire than in previous case.

some

Less

90000

not a max.,

less than max.

N S

Ex 3. A wire moved parallel to B: =

vv

||

00

The wire cuts ________________B field lines.

Because the angle between v and B is ____________

Fmag is _____________

_______ V is induced in the wire.

In symbols: v B

none of the

No

zero

zero

min. V (=0)

Notice that in all three cases above, a ________________________________ was set up that is a result of the________________________ between the wire and B field.But unless the wire is attached to a circuit, _____________________________ .

Caseangle between

v and B (0)

induced potential

difference

1

2

3

In sum:

0

90

between 0-90

max.

min.

in between

potential

difference

relative motionno current

will flow

Electromagnetic devices use magnetism and electricity:

1. motors (based on Case _____ from first slide)

A ___________ in wire experiences a force due to B.

If that force can be made to ____________________,

then you can transform:

Another example of this is a ___________________

It is a ______________________ that is attached to a paper cone. When current passes through the wire,the magnetic force makes the paper cone move.

A

______________ energy _______________ energy

turn a coil of wire

electrical mechanical

speaker

coil of wire

electrical

sound

current

______________ energy _______________ energy______________ energy _______________ energy _______________ energy

mechanical

Simple DC motor

Instead ofpermanentmagnets,you can use the current from thebattery tocreateelectromagnetsto provide theB field.

v

B

F

vB

F

Side view of motor case:

Simple speaker:

House Speaker:

2. generators (based on Case _____ from first slide)

When a wire with no current is moved, the Fmag

pushes the ____________ to the ends of the wire, but

___________________unless the wire is ______________

__________________

C

electricalmechanical

N S

v

electronsno charge flows connected

to a circuit:

With a complete circuit, there is ______________, and

_____________ energy ______________ energy

current

Asimple AC generator:

Instead ofpermanentmagnets,you can use some of the output current to createelectromagnetsto provide theB field.

v

B field has a constant direction, so Fmag dependson the direction of v:

turn counter-clockwise

F

The electromagneticforce pushes chargesout the "short" wire

v

F

B

B

v

Now coil has turned so that it is vertical:

turn counter-clockwise

v

No force on electronsor induced voltagebecause v and Bare parallel (or anti-parallel)

B

B

v

Now coil has made another ¼ turn or so…

turn counter-clockwise

F

The electromagneticforce pushes chargesout the long end –inother words…in theopposite direction!!!

v

F

B

B

Now imagine lookingstraight down therings

Then you would see somethinglike this:

And, as the coilswere turned, itwould look like:

I

Direction of induced current:

t

I t

I t

I t

B always left

This

is

how

AC

is

made!

Electrical motors and generators are basically the _______

devices—they have _________ that turn in _____________:

same

wires B fields

motor generator

________________ in

________________ out

_______________ in

______________ out

electric energy

mech. energy

mech. energy

electric energy

3. Credit cards have a unique ____________ strip. Moving the card changes the __________ in the ATM.This induces a unique ____________ in a coil in the ATM.

4. Guitar pickups are coils wrapped around ___________.When a ____________ guitar string vibrates, it changes the __________ of the magnet. This induces a _______________ in the coil which is amplified and sent to a _____________ . .

Instead of moving awire through a B fieldto induce a voltage, you can also change the B field near the wire by______________________moving the magnet

magneticB field

voltage

magnets

B field

steel

voltage

speaker

5. Transformers two ________________ wrapped around the same

____________:iron

core

A. ______current in _______________ coil causes…B. …the __________ at ________________ coil to change…C. …which induces a ______________________________ in the _________________ coil.

If N2 ___ N1, then voltage is ___________________________ .

If N2 ___ N1, then voltage is ___________________________ .

AC primaryB field secondary

potential difference (voltage)secondary

wire coils

iron core

stepped up (increased)stepped down (decreased)

><

Voltages are ____________________ for long-

distance

transmission because less heat or ________ energy

is lost. Once they reach their destination, they

are _____________________ for safe use.

Power in =

Pin =

VinIin =

VinIin =

VinIin =

Step down:

Step up:

VoutIout

VoutIout

Pout

VoutIout

Power out

stepped up

I2R

stepped down

Energy is neither _______________ nor _______________ :created destroyed

More than meets theeye….

6. In antennas: -________________are accelerated _________________-As a result, ________________________ radiation is emitted from the antenna as ____________.-The radiation is made up of: 1/ an ____________ field and 2/ a _____________ field

As they move, the fields are constantly________________ . As one field changes, it induces _______________________________ .These waves move out _____________________________ . Radio waves, __________________and ___________ are all forms of ___________________ _________________ and travel at the speed of __________ .

electrons up and downelectromagnetic

waves

electricmagnetic

changingthe other field and vice versa

at the speed

of lightx-rays electromagnetic

visible light

radiation light

This is an example of electromagnetic ________________ .

In this way, __________ waves can transmit ___________

by means of their _______________ through a vacuum.

induction

When these fields reach an antenna, the fields

force the _________________ in the antenna to accelerate

at the exact same _______________ .

Cell phones and microwave ovens also transmit

energy by means of electromagnetic ____________.

energy

fields

electronsfrequency

waves

E & M