III. Electromagnetic Induction. Oersted: Moving charge (I) exerts a _____________________. N’s 3rd law: A magnet exerts a __________________________ . force on a magnet force on a moving charge magnet Dq S N v v A: a wire ________ w/ current q at rest C: wire with ____________ B: __________ __________ moving charge no current but moving The charges in ____________________ experience a _________________ force Fmag. all 3 cases magnetic

For any charge q moving with a velocity v through a B: Magnitude (strength) of Fmag: Fmag = ________________, q is angle between v and B. Notice: If q = 0, then Fmag = _______ . Direction of Fmag. Fmag is _______________________ to v and B. qvB sinq perpendicular Ex: A charged particle moves at different angles to B. Assume v is the direction of the charge's motion. 450 900 00 q = _____ q = _____ q = _____ z x y z x y z x y Fmag=0 Fmag B B B Fmag v v v max. med. min. Fmag = _______ Fmag = _______ Fmag = _______

> > Ex: The force between 2 current-carrying wires is used to define the ________________: ampere I > wire 1 Fmag Fmag I > wire 2 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. ampere 1 meter 2 x 10-7 N attractive

Case C (again): A wire conductor moved in a B field the magnet could be moved N S E Fmag causes the ______________________________________ This ___________________________ an electric field in the wire, which results in an _______________________________ or _________________________between the ends of the wire. electrons to move to one end of the wire. induces (or sets up) induced potential difference, induced voltage Electromagnetic Induction: “______________ motion between a conductor and a B field induces (creates) a ___________________ in the conductor.” Relative potential difference

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 Ex 1. A wire moved between two magnets. Its velocity v is perpendicular to B: q = ______ 900 v N S 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  directly through 900 max. Maximum max. V

Ex 2. A wire moved at an angle: < q < 00 900 v N S 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 not a max., less than max. Less

Ex 3. A wire moved parallel to B: q = 00 v v N S 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 zero zero No || min. V (=0)

induced potential difference 1 2 3 In sum: angle between Case v and B (0) induced potential difference 1 2 3 90 max. between 0-90 in between min. potential 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, _____________ ________________ . difference relative motion no current will flow

Electromagnetic devices use magnetism and electricity: 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: A current turn a coil of wire ______________ energy  _______________ energy electrical mechanical 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. speaker coil of wire ______________ energy  _______________ energy  _______________ energy ______________ energy  _______________ energy electrical mechanical sound

Simple DC motor Instead of permanent magnets, you can use the current from the battery to create electromagnets to provide the B field. F v B B v F

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 electrons no charge flows connected to a circuit: N S v current With a complete circuit, there is ______________, and _____________ energy  ______________ energy mechanical electrical

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

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

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

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

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

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

Electrical motors and generators are basically the _______ devices—they have _________ that turn in _____________: same wires B fields motor generator ________________ out mech. energy electric energy ______________ out _______________ in mech. energy ________________ in electric energy

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 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 _____________ . . magnetic B field voltage magnets steel B field voltage speaker

5. Transformers  two ________________ wrapped 5. Transformers  two ________________ wrapped around the same ____________: wire coils iron core iron core AC primary ______current in _______________ coil causes… …the __________ at ________________ coil to change… …which induces a ______________________________ in the _________________ coil. B field secondary potential difference (voltage) secondary If N2 ___ N1, then voltage is ___________________________ . > stepped up (increased) < stepped down (decreased)

VoutIout VinIin = created destroyed Energy is neither _______________ nor _______________ : Power in = Pin = VinIin = Power out Pout VoutIout Step up: VinIin = VoutIout VoutIout Step down: VinIin = Voltages are ____________________ for long-distance transmission because less heat or ________ energy is lost. Once they reach their destination, they are _____________________ for safe use. stepped up I2R stepped down

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 visible light x-rays electromagnetic radiation light

This is an example of electromagnetic ________________ . In this way, __________ waves can transmit ___________ by means of their _______________ through a vacuum. induction E & M energy fields 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 ____________. electrons frequency waves