IB Physics D.4

electromagnetic induction

occurs when there is relative motion between a magnetic field and a conductor, inducing an EMF

Electromotive force (EMF)

total energy transferred in the source per unit charge passing through it

magnetic flux density is the same as

magnetic field strength

magnetic flux density

describes how close together the field lines are or how many field lines pass through a particular area

Faraday’s Law

the magnitude of the induced emf is equal to the rate of change of flux

methods to induce magnetic field flux

change B, change area A of loop or surface, or change the relative angle between the loop of wire and field

Magnetic flux linkage

product of magnetic flux and the number of turns in the coil = N * phi

a current-displacement graph will appear as the derivative of

a flux-displacement graph

use the ___ part of a conductor for length (for ex. in BIL)

vertical

the BIL force ___ motion of a moving conductor

opposes

Lenz’s law states

An induced current (and emf) will always act to oppose the change that caused it

label the parts on the above image (left to right)

magnets, coil, steady rate of rotation, magnetic field lines, brushes in continuous contact with the commutator rings, slip rings, alternating potential difference, meter pointer swings from side to side

why is a magnetic flux-time graph sinusoidal for a coil rotating in a constant magnetic field

1. coil perpendicular to B-field = max flux

2. coil parallel to B-field = 0 flux

3. coil perpendicular to B-field in opposite direction = -max flux

4. etc.

why is an emf-time graph sinusoidal for a coil rotating in a constant magnetic field

1. coil perpendicular to B-field = max flux = 0 rate of change = 0 emf

2. coil parallel to B-field = 0 flux = max rate of change = max emf

3. coil perpendicular = 0 emf

4. coil parallel to B-field in opposite direction = 0 flux = -max rate of change = -max emf

an increase in the frequency with which a coil is rotated leads to an ___ in the magnitude of emf

increase (increase in frequency = decrease in t = increase in emf)

current also equals

q/t

changing flux generates ____ and ____

emf, current

denser magnetic field = ____ magnetic flux

higher

for phi = BAcostheta, theta =

degrees the conductor is off perpendicular

reversing a magnetic field changes the ___ of the flux

sign

slope of a flux time graph

emf

sum of emfs =

IR + IR …, is a version of conservation of energy

a generator turns ___ energy into ___energy

mechanical (kinetic), electrical

a motor turns ___ energy into ___energy

electrical, mechanical (kinetic)

know how to derive emf = BvL

!!!

magnetic flux

amount of magnetic field lines that cut perpendicularly through a cross sectional area