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 S A > > > > > > > > > > > > > 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 > > > > > > > > > > > > > > > > D

N S qq B: __________ __________ A: a wire ________ w/ current magnet C: wire with ____________ The charges in ____________________ experience a _________________ force F mag. v v force on a magnet force on a moving charge at rest moving charge no current but 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 F mag : F mag = ________________,  is angle between v and B. Notice: If  = 0, then F mag = _______. Direction of F mag. F mag 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 B F mag z x y v B z x y v B  = _____ F mag = _______ max. med.min. F mag =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. > > F mag I I wire 1 wire 2 ampere 1 meter 2 x N attractive

Electromagnetic Induction: “______________ motion between a conductor and a B field induces (creates) a ___________________ in the conductor.” Case C (again): A wire conductor moved in a B field or __________________________________ N S F mag 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 difference Relative 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 F mag 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 force v of the charge potential difference 90 0 directly through Maximum max. V 90 0 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 ____________ F mag is ____________________ _______ V is induced in the wire than in previous case. some Less not a max., less than max.

N S Ex 3. A wire moved parallel to B:  = v v || 0 The wire cuts ________________B field lines. Because the angle between v and B is ____________ F mag is _____________ _______ V is induced in the wire. In symbols: v B  none of the No 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, _____________ ________________. Case angle between v and B ( 0 ) induced potential difference In sum: 0 90 between 0-90 max. min. in between potential difference relative motion no 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 mechanical

Simple DC motor Instead of permanent magnets, you can use the current from the battery to create electromagnets to provide the B field. v B F v B 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 F mag pushes the ____________ to the ends of the wire, but ___________________unless the wire is ______________ __________________ C electricalmechanical N S v electrons no charge flows connected to a circuit: With a complete circuit, there is ______________, and _____________ energy  ______________ energy current

A simple AC generator: Instead of permanent magnets, you can use some of the output current to create electromagnets to provide the B field.

v B field has a constant direction, so F mag depends on the direction of v: turn counter- clockwise F The electromagnetic force pushes charges out the "short" wire v F B B

v Now coil has turned so that it is vertical: turn counter- clockwise v No force on electrons or induced voltage because v and B are parallel (or anti- parallel) B B

v Now coil has made another ¼ turn or so… turn counter- clockwise F The electromagnetic force pushes charges out the long end –in other words…in the opposite direction!!! v F B B

Now imagine looking straight down the rings Then you would see something like this: And, as the coils were turned, it would look like:

I Direction of induced current: t I t I t I t B always left This is how AC is m a d e !

Electrical motors and generators are basically the _______ devices—they have _________ that turn in _____________: same wiresB fields motorgenerator ________________ in ________________ out _______________ in ______________ out electric 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 a wire through a B field to induce a voltage, you can also change the B field near the wire by ______________________ moving the magnet magnetic B 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 N 2 ___ N 1, then voltage is ___________________________. AC primary B 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 = P in = V in I in = V in I in = Step down: Step up: V out I out V out I out P out V out I out Power out stepped up I2RI2R stepped down Energy is neither _______________ nor _______________ : createddestroyed

More than meets the eye….

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 down electromagnetic waves electric magnetic changing the other field and vice versa at the speed of light x-rayselectromagnetic 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 electrons frequency waves E & M