physics magnetism

F = I•L•B

B•I•L•sin0

what is a generator, and how does it differ from a motor?

a motor converts electricity to work, whereas a generator converts work to electricity (no power source needed).

how do you induce a current

change the flux

flux definition

magnetic field lines that pass through the center of the wire loops

why will dropping a magnet on a hard surface weaken it?

the domains are jostled out of alignment

magnetic field unit and symbol

unit: tesla, symbol: T

alternating current (ac)

a flow of electric charge that regularly reverses its direction

your classmate says that, if you crank the shaft of a conventional motor manually, the motor becomes a generator. do you agree or disagree and why?

agree; any coil of wire spun in a magnetic field that cuts through magnetic field lines is a generator

how can a piece of iron be induced into becoming a magnet? for example, if you place a paperclip near a magnet, it will itself become a magnet. why?

align the domains with the magnetic fields

where do magnetic fields form?

around magnetic materials (like iron) and also around moving electrical charges

more loops

bigger voltage

how can voltage be induced in a wire with the help of a magnet?

by moving the magnet past the wire or into the coil. the iron has electrons that don't completely cancel out, so if you align the domains of the wire with the coils, it induces the iron wire.

residents of northern canada are bombarded by more intense cosmic radiation than are residents of mexico. why is this so?

charged particles moving downward at polar locations move more nearly parallel to earth's magnetic field lines (less deflection) than particles moving downward in tropical locations.

what is the major difference between electric charges and magnetic poles?

charges can be isolated, whereas poles cannot

what is a magnetic domain?

clusters of aligned iron atoms

what is the shape of the magnetic field that surrounds a current carrying wire?

concentric circles (circles getting bigger and bigger)

according to most geophysicists, what is the probable cause of earth's magnetic field?

currents in earth's molten interior

what is meant by magnetic declination?

difference between geographic north and magnetic north

why do some pieces of iron behave as magnets, while other pieces of iron do not?

domains in some are aligned

every spinning electron is a tiny magnet. since all atoms have spinning electrons, why are not all atoms tiny magnets?

electrons spin in opposite directions, so their fields cancel out

force of magnetic field

f=q•v•β•sinθ

what is so special about iron that makes each iron atom a tiny magnet?

fields of iron's electrons do not entirely cancel out

moving perpendicular to field

greatest force

direct current (dc)

has constant directions

lenz's law

induced magnetic field's direction will oppose change; charges going in one direction want to stay in that direction

two separate but similar coils of wire are mounted close to each other, as shown below. the first coil is connected to a battery and has a direct current flowing through it. the second coil is connected to a galvanometer. how does the galvanometer respond when the switch in the first circuit is closed? when the current is steady after the switch is closed? when the switch is opened?

induction occurs only for a change in intercepted magnetic field. pulse occurs when switch in the first circuit is closed and current in the coil increases from zero. when current in first coil is steady, no current induced in secondary; galvanometer reads zero. the needle swings in opposite direction when switch is opened and current falls to zero.

what role does earth's magnetic field play in cosmic ray bombardment?

it deflects incoming charged cosmic rays

field lines magnetic field

magnetic field is strongest where lines are closer together; flow from north to south in a magnet

induced magnetic field defintion

magnetic inertia; opposes change

a magnet moved into a coil of wire will induce voltage in the coil. what is the effect of moving a magnet into a coil with more loops?

more coils = greater induced voltage

what must a charged particle be doing in order for it to experience a magnetic force?

moving across magnetic field lines

magnetic field definition

moving charges warp the space around it, and create a magnetic field around the charge

what are magnetic pole reversals and what evidence is there that the earth's magnetic field has undergone pole reversals throughout its history?

n changes to s, s to n; magnetism found in rock strata

moving parallel to field

no force

magnetic poles are always paired

north pole and south pole

how do magnetic poles interact?

opposites attract; likes repel

in what direction relative to a magnetic field does a charged particle travel in order to experience maximum magnetic force? minimum magnetic force?

perpendicular to the field lines; parallel to the field lines

larger charges result in

proportionally larger forces

larger magnetic fields result in

proportionally larger forces

larger velocities result in

proportionally larger forces

if you place a chunk of iron near the north pole of a magnet, attraction will occur. why will attraction also occur if you place the iron near the south pole of the magnet?

the attraction is due to inducing opposite polarity. north induces south; south induces north. (similar to electric charge induction and charge polarization)

a magician places an aluminum ring on a table, underneath which is hidden an electromagnet. when the magician says "abracadabra" (and pushes the switch that starts current flowing through the coil under the table), the ring jumps into the air. explain her trick.

the changing magnetic field produced when current flows induces current in the aluminum ring, which in turn generates a magnetic field that opposes the field produced by the magnet beneath table. the ring momentarily becomes a magnet that is repelled by the hidden magnet.

since magnetic electric charges make magnetic fields

the induced current will have an induced electric field

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?

the wire is aligned with the magnetic field (parallel). in order to experience a force, the wire must be at a nonzero angle to the field. the maximum force occurs at an angle of 90º to the field

when a strip of magnetic material variably magnetized, is embedded in a plastic credit card that is moved past a small coil of wire, what happens in the coil? what is the practical application of this?

voltage is induced in the coil; a credit card reader

a strong magnet attracts a paperclip to itself with a certain force. does the paperclip exert a force on the strong magnet? if not, why not? if so, does it exert as much force on the magnet as the magnet exerts on it? defend your answer.

yes; the forces are equal and opposite, in accord with newton's third law

if a car made of iron and steel moves over a wide closed loop of wire embedded in a road surface, will the magnetic field of earth in the loop be altered? will this produce a current in the pulse? can you think of a practical application of this?

yes; yes; triggering automobile traffic lights

right hand rule and left hand rule

(think of x y and z axis)