EEE1012Introduction to Electrical &

Electronics EngineeringChapter 8: Magnetism

by Muhazam Mustapha, October 2010

Learning Outcome

• Be able to utilize and understand the concepts and formula of magnetism

• Be able to utilize and understand some of the processes and formula of electromechanics

By the end of this chapter students are expected to:

Chapter Content

• Units and Formula of Magnetism

• Units and Formula of Electromechanical Systems

Magnetism

Magnetism

• Magnetism is a phenomenon that comes alongside electrodynamic phenomenon

• Moving electrons are known to have spin that is theoretized to cause magnetism

• The current (opposite of electron) flow causes magnetic field to form circularly according to right hand grip– Current is in thumb direction– Magnetic field direction is the fingers direction

Magnetism

• Right hand grip rule:

Magnetism

• Right hand grip rule:

Magnetic Flux

• Magnetic flux is the imaginary entity that is considered to form magnetism

• The direction of magnetic flux is the direction of compass aligned with the flux (from magnetic north pole to south pole)

• Units and symbols:– Magnetic Flux: Ф, Wb (Weber)– Magnetic Flux Density: B, Wb/m2 or T (Tesla)– Magnetic Flux Intensity: H, A/m

Magnetic Flux

Magnetic Flux

• Relationship:

A

BdA

AB

LiN

If flux density is constant

Ampere’s Law

Statement:

Integral of vector magnetic field intensity H around a closed path is equal to the

total current inside the path

id lH iHdl If the direction of the closed loop is the same as the field direction

Ampere’s Law

• For a single conductor flowing a current of i, this reduces to:

r

iH

2

Integration along circular path centered at the conductor; same direction as the flux

Basic of Electromechanical Energy Conversion

Lorenz’s Force Law

• For motor action:

f = il×B

• If the vectors l and B are perpendicular,

f = Bli

• Right hand rule:Force

Current

Flux

f = mechanical forcei = currentl = conductor lengthB = flux density

Lorenz’s Force Law

• For generator action:

e = Blv

e = voltagev = conductor speedl = conductor lengthB = flux density