MAGNETISM A magnet is a material or object that produces a magnetic field with a North and South Pole.

Magnetism: an invisible force that pushes or pulls magnetic material.

THE ANCIENT GREEKS DISCOVERED A NATURALLY MAGNETIC ROCK 2500 YEARS AGO – DO YOU KNOW WHAT IT IS CALLED?

HISTORY OF MAGNETS

MAGNETIC DOMAINS Regions of atoms that

have the same magnetic polarity (N/S Alignment).

Mini-magnets. Unmagnetized Iron

Magnetic domains point in different directions.

Magnetic fields cancel each other out.

Magnetized Iron Magnetic domains are

lined up in the same direction

Magnetic fields amplify each other.

MAGNETIC FORCE

The direction of the magnetic force is from NORTH to SOUTH

TWO LIKE POLES TOGETHER WILL HAVE A

FORCE OF REPULSION

TWO UNLIKE POLES GIVE A FORCE OF ATTRACTION

Can you explain what the lines of force show?

Where is the strongest part of the field?

Where is the weakest part of the field?

Small particles of iron filings are pushed into patterns by a magnetic field. If we sprinkle iron filings on a piece of paper over a magnet we can see...The lines of force are very close together here – the field is very strong.

The lines of force are further apart here – the field is weaker.

A line of force links one pole of a magnet to the other pole.

FOR EACH PICTURE IDENTIFY THE FORCE ILLUSTRATED……………

A)

B)

MAGNETIC COMPASS

CONTAINS A MAGNET THAT INTERACTS WITH THE EARTH'S MAGNETIC FIELD AND ALIGNS ITSELF TO POINT TO THE MAGNETIC NORTH AND SOUTH POLES.

North magnetic pole located at

south geographic pole

South magnetic pole located at

north geographic

pole.

Magnetic declination•is the angle between magnetic north and geographic true north. •Angle varies by location •Ranges from 0⁰ to 25 ⁰

TYPES OF MAGNETSElectromagnet

coil of wire that acts as a magnet when an Electric

current is passed throughit.

stops being a magnet when the current stops.

Often, the coil is wrapped around a

core of ferromagnetic material like steel, this enhances the coils magnetic field.

PERMANENT MAGNET an object made from a

material that is magnetized

& creates its own

persistent magnetic field.

Example refrigerator magnet

USES OF MAGNETS Levitating trains

(MagLev) Treat depression &

chronic headaches Electric motors Stereo Speakers Credit Cards

MAGNETIC FIELD

MAGNETIC FIELD•Produced by electric currents •Defined as a Region where magnetic forces can be detected. •Has a North & South magnetic pole•The SI unit for a large magnetic field is the Tesla •The SI unit for a smaller magnetic field is the Gauss

•(1 Tesla = 10,000 Gauss).

The strength of a magnetic field (B) is related to the amount of magnetic force (F) that is applied to a moving test charge when it is at a given location in the field.

B = F magnetic qv

q = test charge magnitude v = speed of the charge

MAGNETIC FIELD STRENGTH

SAMPLE PROBLEMA proton moving east experiences an upward force of 8.8 x 10-19 N due to the Earth’s magnetic field. The field has a strength of 5.5 x 10-5 Teslas (T) to the north.

Find the speed of the proton.q = 1.60 x 10-19 C B = FmagneticB = 5.5 x 10-5 T qvFmagnetic = 8.8 x 10 10-19 N

v = Fmagnetic qB

Fmagnetic = qvb SinѲ

Solution

v = 8.8 x 10-19 N

(1.60 x 10-19 C) (5.5 x 10-5 T)

1.0 x 10 5 m/s

DIRECTION OF MAGNETIC FORCE

The direction of the magnetic force is perpendicular to

the plane of the magnetic field and to the direction of

the charge.

USE THE RIGHT HAND RULE!!!

MAGNETIC FORCE IN A CURRENT CARRYING WIRECurrent carrying wires that are placed in a magnetic field also experience a magnetic force.

I – C

UR

RE

NT

F- FORCE

WIRE

MAGNITUDE OF MAGNETIC FORCE

The magnitude of the magnetic force can be written in terms of the current (I) flowing through the length of the wire (L).

Magnetic Force in a Current Carrying wire

F = BIL

SAMPLE PROBLEMA 10.0 m long power line carries a current of 20.0 Aperpendicular to the Earth’s magnetic field of5.5 x 10 10-5 T. What is the magnetic force experienced by the power line?

I = 20.0 AB = 5.5 x 10 10-5 TL = 10.0 m

F = BIL

F = (5.5 x 10 10-5 T)(20.0 A)(10.0 m) = 0.011 N

MAGNETIC FIELDS FROM ELECTRICITYCharges that are in motion (an electrical current) produce magnetic fields.

Magnetic field moves around a wire with a current in a circular fashion.

Which direction???

MAGNETIC FIELD IN A CURRENT CARRYING CONDUCTOR

Right Hand Rule

1. Thumb goes in the direction of the current.

2. Fingers wrap around wire in the direction of the magnetic field.

ELECTROMAGNETArranging wire in a coil and running a current through produces a magnetic field that is similar to a bar magnet.

SOLENOID

• A coil wound into a tightly packed helix.

•Produces a uniform magnetic field when a charge is applied to it.

PRACTICE PROBLEMS1. A particle with a positive charge of q moves with a speed v and passes through a

magnetic field B parallel with the speed v. What is the magnitude of the magnetic force on the particle?

a) F = qvBb) F = -qvBc) F = 0d) F = qvB/2e) F = -qvB/2

2. In the figure below, a magnetic field of .01 T is applied locally to a wire carrying a current of intensity I = 10A. What is the magnitude of the magnetic force applied to the wire?

a) F = .3Nb) F = .4Nc) F = .5Nd) F = 1Ne) F = 3N

PRACTICE PROBLEMS CONT A wire 36 m long carries a current of 22A from east to west. If the

maximum magnetic force on the wire at this point is downward(toward Earth) and has a magnitude of 4.0 X 10-2 N, find the magnitude and direction of the magnetic field at this location.

Given: l = 36 m I = 22A Fmagnetic = 4.0 X 10 -2 N Unknown: B = ???

Fmagnetic = B ∙ I ∙ l then B = Fmagnetic

I l

B =

PRACTICE PROBLEM SOLUTIONS1. A particle with a positive charge of q moves with a speed v and passes through a magnetic field B parallel with the speed v. What is the

magnitude of the magnetic force on the particle?

a) F = qvBb) F = -qvBc) F = 0d) F = qvB/2e) F = -qvB/2

Solution: c)The force F, on the charge q moving with a velocity v in a magnetic field b is F = q(v x B).The magnitude of F is F = q·v·B·sinθ where θ is the angle between v and B. In our case the v and B vectors are parallel, so sinθ = 0. In conclusion F = 0.

2. In the figure below, a magnetic field of .01 T is applied locally to a wire carrying a current of intensity I = 10A. What is the magnitude of the magnetic force applied to the wire?

a) F = .3Nb) F = .4Nc) F = .5Nd) F = 1Ne) F = 3N

Solution: b) The magnitude of a magnetic force applied to a current-carrying wire situated in a magnetic field is F = I·B·l·sinθ

where: · l is the length of the wire,· B is the magnetic field strength· I is the current in the wire,· θ is the angle between the wire and the magnetic field. In our case sinθ = 4/l so l·sinθ = 4m.

F = 10A·.01T·4m = .4N

PRACTICE PROBLEM SOLUTIONS A wire 36 m long carries a current of 22A from east to

west. If the maximum magnetic force on the wire at this point is downward(toward Earth) and has a magnitude of 4.0 X 10-2 N, find the magnitude and direction of the magnetic field at this location.

Given: l = 36 m I = 22A Fmagnetic = 4.0 X 10 -2 N Unknown: B = ???

Fmagnetic = B ∙ I ∙ l then B = Fmagnetic

I l

B = 4.0 X 10-2 N = 5.0 X 10-5 T (22A)(36m)