Magnetism

INTRO Aurora Borealis, or northern lights

People have been aware of magnets and magnetism for thousands of years, in region of Asia

Minor called Magnesia, now part of western Turkey

Magnetic rock, Lodestone or Magnetite

South-pointing spoon of a Han Dynasty (206 BC–220 AD) a device for divination

First real application of magnets was used for navigation

• The compass was used in Song Dynasty China by the military for navigational orienteering by 1040-1044, and was used for maritime navigation by 1111 to 1117

• Chinese mariners the floating needle in a bowl until the 16th-century.

INTROEarly modern dry compass suspended by a gimbal (1570)-freely pivoting needle on a pin

A simple dry magnetic portable compass

A smartphone that can be used as a compassbecause of the magnetometer inside

Magnetometers

• measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space

Todays Application

• giant magnetoresistance (and its applications to computer memory (used to read data in hard disk drives, biosensors..etc)

INTRO

Electric motors • powering refrigerators,

starting cars, and moving elevators- contain magnets

Electric motors

INTRODUCTION

Generators• Generators, whether

producing hydroelectric power or running bicycle lights, use magnetic field

Bike generator

INTRODUCTIONRecycling facilities employ magnets to separate iron

INTRODUCTIONmagnetic containment of fusion as a future energy source

The Energy Source of Tomorrow…/-! ?

INTRODUCTIONMagnetic resonance imaging (MRI)

Japan's maglev train breaks world speed record with 600km/h test run

levitation of high-speed trains

INTRODUCTION

Large Hadron Collider

MAGNETS

MAGNETS

• All magnets attract iron

• magnets may attract or repel other magnets

• all magnets have two poles

• two poles e north magnetic pole and the south magnetic pole

• (or more properly, north-seeking and south-seeking poles, for the attractions in those directions).

UNIVERSAL CHARACTERISTICS OF MAGNETS AND MAGNETIC POLES

• like poles repel and unlike poles attract.

• (Note the similarity with electrostatics: unlike charges attract and like charges repel.)

• impossible to separate north and south poles in the manner that + and − charges can be separated

MISCONCEPTION ALERT: EARTH’S GEOGRAPHIC NORTH POLE HIDES AN S• Earth acts like a very large

bar magnet with its south-seeking pole near the geographic North Pole

• Confusion - “North Pole” has come to be used (incorrectly) for the magnetic pole that is near the North Pole. Thus, “North magnetic pole—it should be called the South magnetic pole.

• The north pole of a compass needle is a magnetic north pole. It is attracted to the geographic North Pole, which is a magnetic south pole (opposite magnetic poles attract)

Magnetic atoms have both a north pole and a south pole, as do many types of subatomic particles, such as electrons,

protons, and neutrons.

• North and south poles s occur in pairs.

• Attempts to separate them result in more pairs of poles.

• Continue to split the magnet, an iron atom with a north pole and a south pole—these, too, cannot be separated

Section Summary

• Magnetism is a subject that includes the properties of magnets, the effect of the magnetic force on moving charges and currents, and the creation of magnetic fields by currents.

• There are two types of magnetic poles, called the north magnetic pole and south magnetic pole.

• North magnetic poles are those that are attracted toward the Earth’s geographic north pole.

• Like poles repel and unlike poles attract.

• Magnetic poles always occur in pairs of north and south—it is not possible to isolate north and south poles.

Ferromagnets

• ONLY iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects called ferromagnetic, after the Latin word for iron, ferrum

neodymium

• Ferromagnetic materials can also be magnetized themselves—can be induced to be magnetic or made into permanent magnets.

The regions within the material called domains act like small bar magnets

• An unmagnetized piece of iron-randomly oriented domains

• Individual atoms are aligned within domains; each atom acts like a tiny bar magnet.

Demagnetizing • demagnetized by hard

blows (hitting it with a hammer) or by heating it in the absence of another magnet.

Demagnetizing

Electromagnets

• Danish scientist (1777–1851)a compass needle was deflected by a current-carrying wire

• Electromagnetism is the use of electric current to make magnets

• Temporarily induced magnets are called electromagnets

• wrecking yard crane, particle accelerator, medical imaging machines

• Iron filings near (a) a current-carrying coil and (b) a magnet act like tiny compass needles, showing the shape of their fields.

• impossible to separate north and south magnetic poles

• magnetic monopoles, are not observed

No magnetic monopoles

• Space surrounding a mass has gravitational field

• Space surrounding a charge body has electrical field

• Magnetic field is the alteration of the motion of a charge

• A charged body has both electric field and magnetic field

• Greater the speed of charged body, grater the magnitude of surrounding magnetic field

• A magnetic filed is produced by electric charge in motion

Electric current is the source of all magnetism Magnetic field lines

Section Summary

• Magnetic poles always occur in pairs of north and south—it is not possible to isolate north and south poles.

• All magnetism is created by electric current.• Ferromagnetic materials, such as iron, are those that exhibit strong

magnetic effects.• The atoms in ferromagnetic materials act like small magnets (due to

currents within the atoms) and can be aligned, usually in millimeter-sized regions called domains.

• Domains can grow and align on a larger scale, producing permanent magnets. Such a material is magnetized, or induced to be magnetic.

• Above a material’s Curie temperature, thermal agitation destroys the alignment of atoms, and ferromagnetism disappears.

• Electromagnets employ electric currents to make magnetic fields, often aided by induced fields in ferromagnetic materials.