Chapter 24 Magnetic Fields Magnet A substance that

Chapter 24 Magnetic Fields

Magnet • A substance that has polarity

Polarity • Charge separation that results in one end being positive & the other end being negative

Magnets • The ends are called the north & south poles

Magnets • North pole = (+) • South pole = (-)

Magnets • Opposite poles attract & like poles repel

Some metals can become temporary magnets by bringing them close to a strong magnet

Most Permanent magnets are made of ALNICO, an alloy of Al, Ni, & Co

Very strong, but expensive permanent magnets are made of neodymium

Magnetic Field • Space where attractive & repulsive forces act around a magnet

Magnetic Field • Force fields similar to gravitational & electric fields

Magnetic Flux • The number of field lines passing through a surface

Field Strength • Magnetic field strength is proportional to the flux per unit area

A temporary magnet concentrates magnetic field lines and is attracted to a permanent magnet

A temporary magnet repels magnetic field lines and is repelled from a permanent magnet

Electromagnetism • Electric current generates a magnetic field & vice versa

Hans Christian Oersted • First to observe electromagnetic properties

Electromagnetism • Electric field lines & magnetic field lines are perpendicular

First Right-Hand Rule • Explain • (page 497)

Passing a current through a wire wrapped around a piece of metal generates a magnetic field

Electromagnet • Magnet generated by passing a current through a coiled wire

Second Right. Hand Rule • Explain • (page 498)

Magnetism at the atomic level • Results from magnetic fields of electrons

Domain • A group of about 20 10 atoms acting together electromagnetically

Domain • Each domain acts like a dipole (polar unit)

Magnitism • Magnetism occurs when domains are aligned

Passing a current through a wire in a magnetic field exerts a force

Third Right-Hand Rule • Explain • (page 503)

Magnetic Induction (B) • Strength of a magnetic field

Magnetic Force • Proportional to current, field strength, & length of the wire

Magnetic Force F = BIL

Magnetic Induction (B) B = F/IL

Magnetic Induction (B) Measured in teslas (T)

Tesla (T) T = N/Am

Galvanometer • Device used to measure very small currents

Galvanometer • Passing current through a looped wire in a magnetic field creates a force causing the wire to rotate (page 505)

Galvanometers • Use 3 RHR to force a needle to move as current passes through a MF

Galvanometers • Can measure currents as small as -6 10 A

Galvanometers • Cannot rotate more o than 180 or more o than 90 from parallel to B

Electric Motors • Must be able to o spin 360 • Explain (page 506)

Electric Motor Force F = n. BIL

F = force n = # of loops B = magnetic field strength I = current L = length of wire loop

Force on a single charged particle F = Bqv

F = force B = Field strength q = charge v = velocity

FORMULAE • Magnetic Force F= BIL • Electric Motor Force F=n. BIL • Force of single charged particle F=Bqv