Magnetism and Magnetism and ElectromagnetisElectromagnetis

mmSPH4CSPH4C

Permanent MagnetsPermanent Magnets

A permanent magnet has two poles: North A permanent magnet has two poles: North and South.and South.

Permanent MagnetsPermanent Magnets

A permanent magnet has two poles: North A permanent magnet has two poles: North and South. Like poles repel. Unlike poles and South. Like poles repel. Unlike poles attract.attract.

Permanent MagnetsPermanent Magnets

These repulsive or attractive forces can act These repulsive or attractive forces can act at a distance (no contact is required). The at a distance (no contact is required). The region in space over which these forces region in space over which these forces can act is called a magnetic field.can act is called a magnetic field.

Magnetic FieldsMagnetic Fields

The iron filings in The iron filings in the picture below the picture below show the magnetic show the magnetic field lines.field lines.

Magnetic Fields Are Magnetic Fields Are DifferentDifferent

Magnetic lines are Magnetic lines are drawn out of the drawn out of the North Pole and North Pole and into the South Pole into the South Pole but they don’t stop but they don’t stop and start there: and start there: the magnetic field the magnetic field lines are drawn lines are drawn throughthrough the poles. the poles.

No MonopolesNo Monopoles

Every magnet is a dipole: it must have Every magnet is a dipole: it must have two poles. If a dipole magnet is two poles. If a dipole magnet is broken in two,broken in two,

No MonopolesNo Monopoles

Every magnet is a dipole: it must have Every magnet is a dipole: it must have two poles. If a dipole magnet is two poles. If a dipole magnet is broken in two, it becomes two broken in two, it becomes two dipoles:dipoles:

Many DipolesMany Dipoles

Why does this Why does this happen?happen?

Many DipolesMany Dipoles

Why does this Why does this happen?happen?

A bar magnet is A bar magnet is made up of many made up of many smaller dipoles, smaller dipoles, each with North each with North and South poles, and South poles, all aligned.all aligned.

Many DipolesMany Dipoles

Why does this happen?Why does this happen?

A bar magnet is made A bar magnet is made up of many smaller up of many smaller dipoles, each with dipoles, each with North and South North and South poles, all aligned.poles, all aligned.

The dipoles may be The dipoles may be knocked out of knocked out of alignment by heating alignment by heating or otherwise abusing or otherwise abusing the material.the material.

Repairing MagnetsRepairing Magnets

A bar magnet may be re-magnetized by A bar magnet may be re-magnetized by placing it in a magnetic field. This is placing it in a magnetic field. This is induced magnetism. induced magnetism.

FerromagneticFerromagnetic

Not all materials may be easily magnetized. Not all materials may be easily magnetized. Those that can are called Those that can are called ferromagneticferromagnetic. . They include iron ore (lodestone), cobalt, They include iron ore (lodestone), cobalt, zinc, and nickel.zinc, and nickel.

Rare-Earth MagnetsRare-Earth Magnets

The strongest permanent magnets are The strongest permanent magnets are made from rare earth (lanthanoid) made from rare earth (lanthanoid) elements, the strongest of these being elements, the strongest of these being neodymium-iron-boron (NIB) magnets,neodymium-iron-boron (NIB) magnets,

Rare-Earth MagnetsRare-Earth Magnets

The strongest permanent magnets are The strongest permanent magnets are made from rare earth (lanthanoid) made from rare earth (lanthanoid) elements, the strongest of these being elements, the strongest of these being neodymium-iron-boron (NIB) magnets, neodymium-iron-boron (NIB) magnets, now greatly reduced in price and used in now greatly reduced in price and used in children’s toys.children’s toys.

ElectromagnetsElectromagnets

Current (moving Current (moving charge) will also charge) will also produce a magnetic produce a magnetic field. This is called field. This is called Oersted’s Principle.Oersted’s Principle.

Showing DirectionsShowing Directions

To show that a current, To show that a current, field line, or force is field line, or force is directed out of the directed out of the page (towards us), we page (towards us), we draw:draw:

To show that a current To show that a current or field line is directed or field line is directed into the page, we into the page, we draw:draw:

Right-Hand Rule #1Right-Hand Rule #1

When the thumb is pointed in the When the thumb is pointed in the direction of conventional current direction of conventional current flow, the fingers curl in the direction flow, the fingers curl in the direction of the magnetic field.of the magnetic field.

SolenoidsSolenoids

To strengthen and straighten the To strengthen and straighten the magnetic field, we coil the current-magnetic field, we coil the current-carrying wire into a carrying wire into a solenoidsolenoid..

Right-Hand Rule #2Right-Hand Rule #2

When the fingers are curled in the When the fingers are curled in the direction of conventional current direction of conventional current flow, the thumb indicates the flow, the thumb indicates the direction of magnetic North.direction of magnetic North.

Magnetic ForcesMagnetic Forces

Since current will produce a magnetic Since current will produce a magnetic field, the interaction of this field field, the interaction of this field with an with an external external magnetic field will magnetic field will result in a force acting on the result in a force acting on the moving charge. This is the Motor moving charge. This is the Motor Principle.Principle.

Magnitude of ForceMagnitude of Force

The magnitude of the magnetic force The magnitude of the magnetic force FFMM on a current-carrying wire is on a current-carrying wire is directly proportional to the current directly proportional to the current II and length and length LL of the wire and to the of the wire and to the magnitude of the external magnetic magnitude of the external magnetic field field B.B. F B ILM

BB

Note that Note that BB, the magnetic field, is , the magnetic field, is measured in Tesla (T).measured in Tesla (T).

BB

Note that Note that BB, the magnetic field, is , the magnetic field, is measured in Tesla (T). 1 T is a very measured in Tesla (T). 1 T is a very strong magnetic field.strong magnetic field.

1 1T kgC s

Magnitude of ForceMagnitude of Force

The magnitude also The magnitude also depends on the angle depends on the angle between the magnetic between the magnetic field vector and the field vector and the current vector. current vector.

When When = 90 = 90oo, (the current , (the current is moving perpendicular is moving perpendicular to the field), the force is to the field), the force is maximum.maximum.

When When = 0 = 0oo or 180 or 180oo (the (the current is moving current is moving parallel to the field), the parallel to the field), the force is zero.force is zero.

sinBILFM

Direction of Force: Direction of Force: Right-Hand Hule #3Right-Hand Hule #3

The direction of the force The direction of the force is given by another is given by another right-hand rule: if the right-hand rule: if the right thumb follows the right thumb follows the direction of direction of conventional current conventional current flow and the extended flow and the extended fingers point in the fingers point in the direction of the direction of the magnetic field, the magnetic field, the force is in the direction force is in the direction the palm would push.the palm would push.

Quick QuizQuick Quiz

What is the direction of the force (if any) on What is the direction of the force (if any) on the particle in each of the following the particle in each of the following cases?cases?