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

Galvanometers Can measure currents as small as A

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

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

Electric Motor Force F = nBIL

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