Magnetism

Chatfield Senior High

Department of Physics

Magnetism Definition

Property of spin of electrons in magnetic substances

Permanent: (iron)Magnetite

Alnico

Magnetism canalso be created by a electric current

Electromagnet

Earth’s Magnetic Field

Magnetic Field Line Rules

Field lines go from North to South

Field is strongest at the poles

No magnetic monopoles in nature

Attraction and Repulsion of Magnets

Like poles repel

Unlike poles attract

Right Hand Rule

Thumb points in direction of conventional current flow (+ to -)(Note this is different than electron flow which goes from – to + (Thanks Ben Franklin!)

Fingers point in direction of the magnetic field

Right Hand Rule (Current going left)

Right Hand Rule (Current going right)

Magnetic Field Through a Curved Wire

Magnetic north is determined by the thumb, fingers encircle the direction of the current

Application (Solenoid)

Current Flow through two parallel wires

Current flows in same direction (attraction)

Current flows in the opposite direction (repulsion)

If a current is flowing to the right in an uninsulated wire, the magnetic field is…

A. Going clockwiseB. Going counterclockwiseC. Going straight upD. Cannot tell from the information given

The answer is A

If current goes clockwise through a solenoid, the north magnetic field points….

A. To the rightB. To the leftC. UpwardD. Cannot tell from the information given

The answer is A

If current is traveling the same direction in two uninsulated parallel wires, the wires…

A. AttractB. RepelC. Remain the sameD. It is unpredictable

The answer is A

Motors

Transfers electrical energy to mechanical energy

Parts of a Motor

Commutator Armature Magnet Wires

Commutator for AC and DC Circuits

Left Hand Rule for Motors

The Alternator

Generator

Takes mechanical energy and transforms it into electrical energy

Speaker

Try to describe how a speaker works

Speaker

Permanent magnetCoil of wire wound around the magnetAC current goes through a coil and it

causes the cone to vibrate

Microphone

Now can you explain how a microphone works? (Hint: It is the opposite of a speaker)

Tape Recorder / VCR

Transformers!

Robots in Disguise!

Electrical Transformers!

Power Transmission

How transformers work

Power is constant in both coils

You must have AC source for a transformer

Transformers can be step up (increases the voltage) or step down (decreases the voltage)

Transformer Equation

P = VI Power of primary coil = Power of secondary P p = P s

V p I p = V s Is

V p = I s = N p

V s I P N s

Voltage is indirectly related to current and directly related to the winding of wires

Transformer Problem

What is the current and the number of winding of wires in an electrical train set?

V p =120 V V s = 6 V

N p =1000 windings I p = 1.5 AV I = V I(120) (1.5) = 6 I

I= 30 A (or 20 times more)

The number of windings goes down by a factor of 20 or 50 windings in the secondary coil

Tokamak

Princeton Plasma Physics Lab

Yamanashi Maglev Train