yr2 - magnetic fields

• magnetic field strength = M_______ f___ d______

• B= ____/____x_____

• Measured in T____

• magnetic flux density

• B= force / I (current) x L (length)

• Tesla

• Magnetic field lines- Represent the force acting on a f___ i____ north pole

  • they stem from _____ and terminate at the ____

  • proximity relates to _____

• free isolating

  • north , south

  • strength

A ______ charge creates an electromagnetic field

• This charge takes a ______ path in a magnetic field. This is because the force and ________ __ ______ are __________

moving

circular

direction of motion , perpendicular

right hand rule?

• _____ shows the direction of the current in the wire and your _____ , the direction of the magnetic field

thumb , fingers

motor effect?

• when an _____ magnetic field interacts with an _____ one that travel in the same direction.

  • as they are v_____ they “merge” and create a magnetic field around a wire as the magnetic pressure is _____.

external, internal

vectoral , greater

No forces acting upon the wire?

• when the two magnetic fields travel in opposite directions they ____ ___.

  • the magnetic field due to the ____ interacts with the ____ magnetic field

    • this means there is ___ force acting upon the wire so it ___

cancel out

wire, external

no , falls

Flemings left hand rule?

• shows the direction of the _____ acting on a ______ _____ acting on a magnetic field

force , positive charge

B = f/IL equation manipulation

• B = number of ____ _____ per ___ ___

  BA = phi = _______ ____ which is the number of ____ ____ passing through the ______ ___ perpendicular to the ____ ____

• phi = flux which is measured in Wb (_____)

field lines , unit area

magnetic flux, field lines, surface area, surface area

webber

Flux linkage?

• N phi or____ _______ = BANCos theta which is the ____ number of field lines passing through the surfaces that is perpendicular to the surface.

  • measured in Wb ____

flux linkage , total

turns

Faradays Law?

• EMF = - N d__/d_

  • which means the ____ __ _____ of flux linkage OR how quickly we ___ the _____ _____ OR how ______ do the ___ of field lines change

phi, t

rate in change

cut, field lines, quickly, number

Lenz’s Law?

• The negative symbol in faradays law links to how the force ______ must be able to overcome the _____ force to conserve _____ in one direction.

applied , induced , energy

Moving wire in a magnetic field?

• Moving the wire in the magnetic field creates a ____ __ ______ in the upwards (____) sense, therefore all of the ______ fall to the bottom creating a ________ ________.

• The moving wire ____ the magnetic field lines.

• If we place a bulb next to the wire and keep moving the wire then the lines will continue to be cut , creating a continuous ______ ___ so the bulb stays on.

• Once we stop moving the wire , the _____ ___ will stop, the bulb will turn off, and the _____ will stop moving to the bottom and will now wish to ______ the charge in the wire.

• Flemings _____ ___ ___ shows that the force applied is in the right direction however Flemings ____ ____ ___ shows that the force being opposed is in the opposite direction to fulfil _____ ___.

flow of electrons

positive, electrons

potential difference

cuts

induced emf

induced emf

electrons

neutralise

right hand rule

left hand rule

Lenz’s Law

Work done in a moving wire in a magnetic field?

• a force is applied upon some distance

  • W = F X D therefore, W = ___ x _

BIL x S

Faradays law and work done derivation? (1)

• W = F x D

  • F = ___ therefore W = ___S however _= q/t so W = __q_/t

  • W/q = ___/t however W/q = EMF therefore EMF = ___/t

  • /t = V so EMF= __V

BILS , I

BLQS/t

BLS/t , BLS/t

s/t , BLV

Faradays law and work done derivation? (2)

• F = ___ where _ = q/t

  • so F = __q/t

  • however _/t = V

  • F= ___

BIL , I

BLq/t

L/t

Bqv

AC?

• Current flows in ___ _____

  • always generates a constantly ________ magnetic flux

Alternating current

both directions

changing

Transformers

• Used to increase or decrease ______ in the next step by changing the ______ __ ____ in a coil

voltage

number of turns

Induced EMF in transformers

• -n dphi/dt₁ = -n dphi/dt₂

• If we _____ 100 field lines then 100 field lines must also be ___.

induce , cut

Voltage and number of turns

V_{_}/ V_{_} = N_{_}/ N_{_}

V_P/V_S = N_P/N_S

Transformer efficiency

• % = I_- V_- / I_- V_-

  • Increase efficiency- place ___ closer to increase the rate in change in ___ ______ to increase the _______ ___

  • or _____ the ___

    • Reduce heat energy loss- insulate the ___ core with ______ (_________) to reduce (_____) currents flowing to the ___ core

      • Reduce resistivity- use wires with a large ___-_______ ____ as R = __/_

• % = I_S V_S / I_P V_P

  • coils

  • flux linkage , magnetic flux

  • overlap, coils

    • iron , plastic (lamination) , (eddy) , iron

      • cross-sectional area , R = rho x L / A