IB Physics 2 Electromagnetic Fields and Induction

What is the cause of magnetic fields

moving electric charges

Charge flows from _____ to ______ inside a magnet, and ______ to ______ outside a magnet

South, North, North, South

Dot

Out of page

X

into page

B = (definition and units)

Magnetic field, T (tesla), N/Am

Right hand rule for a straight wire

thumb in direction of current, fingers curl in direction of B

Right hand rule for a wire loop/solenoid

thumb in direction of B (north), fingers curl in direction of current

Right hand rule for a force on a current bearing wire

thumb points to current, fingers point to B, palm is the force (pushing direction) (hand flat)

Right hand rule for a moving charged particle

+right hand

-left hand

thumb is velocity, fingers are B, palm is force

Moving charged particle formula=

Fb=Bqvsin(theta)

For two charged wires, like currents____ and opposite currents ____

attract, repel

Magnetic force on one wire =

F=BILsin(theta)

Formula for magnetic force per unit length between two wires

F/L = μ (I1 x I2)/2πr)

μ =

permeability of free space, 4π x 10^-7 N/A²

F=

BIL, B(ε/R)L

B = (formula)

μI/2πr

A charged particle will follow a _____ path in a magnetic field because…

circular, the magnetic force is always perpendicular to the velocity

The magnetic force does no work on a charged particle since…

the magnetic force is always perpendicular to the motion

Fin =

mac (mass x centripetal acceleration)

qvB =

mv²/r

r =

mv/qB

qV = ½ mv²

for speed as a proton enters a magnetic field

A mass spectrometer is

an analytical tool useful for measuring the mass-to-charge ratio

A mass spectrometer works by

ionizing a sample to create charged particles, accelerating them with an electric field, deflecting them using a magnetic field based on their mass-to-charge ratio, and detecting their positions to produce a mass spectrum

v (speed) = (spectrometer)

E/B (electric field/magnetic field)

emf can be induced in a conductor by

moving a conductor through a magnetic field, and changing the magnetic flux through the conductor

V = (for induction)

V = (for induction in a coil of wire)

BLv

NBLV (N=number of loops)

For two opposing forces:

F=

V=

I=

Fb=

Fapp=

qvB

BLv

BLv/R

BIL

B²L²v/R

Magnetic flux (definition, symbol, units)

number of field lines, Φ phi, Wb (webber, Tm²)

Φ=

BA, BAcos(theta)

Magnetic Flux Density (magnetic field)

number of field lines per unit area, B, T

Magnetic Flux Linkage (definition, formula, units)

product of magnetic flux through a coil of wire and the number of turns of the wire

NΦ=NBAcos(theta)

Wb

Faradays Law

An induced emf is proportional to the rate of change of the flux linkage

emf= -change in (NΦ)/t

An emf vs t graph is made from a Φ vs t graph by

graphing the negative derivative (graph slope but opposite)

Lenz’s Law

the direction of an induced emf is such that it produces a magnetic field whose flux opposes the flux change that induced it

ie: an induced voltage will keep the flux constant

Lenz’s Law is a statement of

conservation of energy: the magnetic force on the current must oppose the motion, or energy would be created

AC generator’s basic principle

Rotating a coil of wire in a magnetic field causes an alternating emf (and current) to be induced in the coil as the magnetic flux linking the coil changes

Max flux in an AC generator happens…

Max emf in an AC generator happens…

…when the normal line to the coil plane is parallel with the field

…when the normal line to the coil plane is perpendicular to the field

Doubling the rate of an AC coil’s rotation

doubles the magnitude and frequency of the induced emf