Chapter 19Magnetism1. Magnets2. Earth’s Magnetic Field3. Magnetic Force4. Magnetic Torque5. Motion of Charged Particles6. Amperes Law7. Parallel Conductors8. Loops and Solenoids9. Magnetic Domains

Magnets What is magnetism? What is a magnet? What is a magnetic pole? How many types of pole there are? Can single poles exist by themselves? How do you make a magnet? What is a induced magnet? Are all materials magnetic? What are hard and soft magnets?

Magnetic Fields What is a magnetic

field? What symbol should

I use for it? How is magnetic

field produced by electric charges?

Is magnetic field a vector? If yes how do I find the direction?

Magnetic Field Lines, sketch

A compass can be used to show the direction of the magnetic field lines (a)

A sketch of the magnetic field lines (b)

Magnetic Field Lines, Examples

Bar Unlike poles Like poles

Earth’s Magnetic Field What is the

source? What is a dip

angle? Dip angles for

equator and poles True North and

South Magnetic Reversal

Magnetic Force Where does it come from? How do I calculate it? What are the SI units What is a Gauss? Some examples

Right Hand Rule #1 How do I find the

direction of the magnetic force?

Right Hand Rule - Example

1. Find the direction of force on a proton moving through a magnetic field (see problem 19.2 for figures).

2. Do the same for an electron.

Magnetic Force on a Current Carrying Conductor

How do I calculate this force?

Torque on a Current Loop What is a current

loop? Remind me, what is

torque? How do I calculate

this torque? What is magnetic

moment? How do I calculate is

from torque?

Example

1. A conductor carries a current of 15 Amps in the +x direction perpendicular to the B field. It experiences a force of 0.12 N/m in the –y direction. Determine the direction and magnitude of the B field.

Example

1. Solve problem 19.12

Electric Motor

Force on a Charged Particle in a Magnetic Field

What is the nature of this force?

How do I calculate this force?

What is a cyclotron equation?

What if V is not perpendicular to B?

Example – Mass Spectrometer

1. See examples 19.3 and 19.6

Example

1. A proton is accelerated through a electrostatic field of 2100 volts. It enters a magnetic field B=0.10T. Find the

1. Velocity of the proton2. Change in Kinetic energy3. Cyclotron radius

Hans Christian Oersted 1777 – 1851 Best known for

observing that a compass needle deflects when placed near a wire carrying a current

First evidence of a connection between electric and magnetic phenomena

Magnetic Fields – Long Straight Wire

If a magnetic field can produce current, can a current produce magnetic field?

How do I calculate this field?

How do I find the direction of this magnetic field?

André-Marie Ampère 1775 – 1836 Credited with the

discovery of electromagnetism Relationship

between electric currents and magnetic fields

Mathematical genius evident by age 12

Ampère’s Law

What is Amperes law?

How do I use it? How about an

example?

Example

1. Find the magnetic field at point P shown in the diagram.

Example

1. Find the magnetic field at a distance of P from each wire shown in the diagram.

Magnetic Force Between Two Parallel Conductors

How do I calculate this force?

What is the final situation?

Example

1. Two parallel wires are 10 cm apart, and carries a current of 10 A.

1. If the current are in the same direction, find the force per unit length exerted by one of the wires on the other.

2. Repeat the problem with the current in opposite direction.

Defining Ampere and Coulomb The force between parallel conductors

can be used to define the Ampere (A) If two long, parallel wires 1 m apart carry

the same current, and the magnitude of the magnetic force per unit length is 2 x 10-7 N/m, then the current is defined to be 1 A

The SI unit of charge, the Coulomb (C), can be defined in terms of the Ampere If a conductor carries a steady current of 1

A, then the quantity of charge that flows through any cross section in 1 second is 1 C

Magnetic Field of a Current Loop How do I calculate

it ?

Magnetic Field of a Solenoid

What is a solenoid?

How do I calculate its magnetic field?

What does it field look like?

Magnetic Field in a Solenoid from Ampère’s Law How do I apply

Amperes law?

Example

1. What current is required in the windings of a long solenoid that has 1000 turns uniformly distributed over a length of 0.40 m in order to produce a magnetic field of magnitude 1.0 x 10-4 T at the center of the solenoid?

Magnetic Effects of Electrons Hey can we talk about electrons, since

they are charge particles, they spin and orbit the nucleus of the atom, they got to have magnetic field

Magnetic Effects of Electrons – Domains Ferromagnetism Domains Permanent magnets