Magnets review

For QM - mainly dealing with movement of charges in magnetic fields

Magnetic field lines point from ___ to _____

north to south

The force 1 magnet exerts on another can be described as: the interaction between ____ and ______

1 magnet and the field of another

Uniform vs non-uniform field - which one changes

uniform does not change at any point, non-uniform changes point to point

uniform vs non uniform field - describe gradient

uniform field gradient = 0

nonuniform field has nonzero spatial gradient

For moving charges at fixed speeds in uniform field: describe the magnetic force the particle experiences

magnetic force of constant magnitude, results in simple motion like circle or helical

for charges and magnetic dipoles moving in non-uniform field - describe force and trajectory of charges

force varies with position, trajectory becomes more complex and can involve changes in speed/direction of motion

an electric current produces a ______

magnetic field

magnetic field lines produced by current in straight wire look like ___

concentric circles with the wire at the center

for straight wire: strength of magnetic field generated is proportional to ___ and inv to ___

prop to current

inv prop to distance from wire

for circular loop of wire - what happens to the field inside the loop

strength of field is prop to ___ and inv to ____

concentrates B inside the loop

prop to current and # of loops, inv to radius of loop

a current loop behaves like a ______

small magnetic dipole with magnetic moment mu = IA

current loop in uniform B = describe net force and torque, and why

zero net force but yes net torque

opposite sides of loop feel equal and opposite forces, so no translation, but yes rotation

current loop in non-uniform B = describe net force and torque, and why

yes net force and yes torque

when B varies over loop, forces on different parts no longer cancel, loop is pulled towards regions of stronger field when mu has component along field gradient

A magnet exerts a force on current carrying wire: direction of force is _____ to direction of current and ____ and direction of B

perpendicular, perpendicular

right hand rule for magnet exerting a force on current carrying wire (F = IL x B)

fingers first go in direction of ___

curl in direction of ____

thumb shows ____

current

magnetic field

force

For magnet exerting a force on a current carrying wire - when is force zero, and when is force max

force is zero when current is parallel with field

force is max when current is perp with field

Freely moving electric charged particles (not in wire) experience ____ when passing thru B

a force when passing thru B

Right hand rule for force on positive charge (F = qv x B)

fingers point in direction of velocity

curl fingers in direction of B field

thumb shows force

use left hand or switch sign for negative particle

for force on charge from B field: when is it zero and when is it max

max when direction of velocity is perpendicular to B field

zero when velocity parallel to B field

magnetic moment is a vector that measures ____ and in what direction it wants to ____

how strongly

an object wants to align with a magnetic field

magnetic dipole moment tells you ____ of object’s magnetism and _____ of its equivalent tiny bar magnet

strength

orientation

a current loop behaves like a tiny dipole with magnetic moment pointing from ___ to ____ inside magnet

south to north

when current loop is placed in external B, it feels _____ that tends to ______

torque T that tends to rotate it so that magnetic moment lines up with B

Lorentz electric component (qE) - acts in direction of ____ for ___, opposite for _____

Can change ____ of particle and ____

E, positive, negative

speed, do work

Lorentz magnetic component (qv x B): acts in which direction

How much work does it do, and what does it do to the trajectory

acts perpendicular to both v and B

does no work, can only change direction, not speed

causes path to curve

Lorentz force right hand rule

point finger in direction of v

curl towards B

thumb shows direction for positive charge, reverse for negative

for lorentz force, when is force max and when is it zero

force is max when v is perpendicular to B

zero when v is parallel to B