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