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Magnetism & Magnetic Fields
April 27, 2020
• Opposite poles attract• Like poles repel• Magnetic poles ALWAYS come in pairs• Magnetic fields are produced by the motion of an electric charge
Magnetism
Atomic Level of Magnetism(source of magnetism)
• Electrons spin about their axis• Electrons orbit around the nucleus
Magnetic Materials• Cobalt• Iron• Nickel
• These are the only three elements that the electron’s spin and orbit align with each other
• Other materials’ spins and orbits cancel out
Magnetic DomainsMagnetic Domain:• A microscopic cluster of atoms with their magnetic fields aligned• Heating or dropping a magnet will weaken it (causing the domains to become unaligned).
Earth’s Magnetic Field• Deflects most of the cosmic ray’s• What is the cause of the Earth’s magnetic field?
Earth’s Magnetic FieldThe north pole of a compass needle is a magnetic north pole. It is attracted to the geographic North Pole, which is a magnetic south pole (opposite magnetic poles attract).
Magnetism
Chapter 36
Right Hand Rule
RightHand Rule: determines the direction of the magnetic field around a currentcarrying wire .
Point your thumb in the direction of the current (I). The curl of your fingers shows the direction of the magnetic field (B).
Right Hand Rule
Alternately, curl your fingers in the direction of the current loop (I). The thumb points in the direction of the magnetic field (B).
Right Hand Rule Symbols• Vector arrows and
loops• A dot “●” means
out of the page• An ex “X” means
into the page• Label the symbols
I = currentB = magnetic field
• "Dots" (●) and "exes" (X) must be in pairs!
RightHand RuleAnimations
Magnetic field around a loop of wire
Magnetic field around a straight wire
I
X
I
I
Generators and Electric Motors
Electromagnetic Induction
Electromagnetic Induction• Electromagnetic Induction: The process of creating a
voltage in a circuit by changing the magnetic field.
Generator Components• Strong magnet or magnetic field• Coil of wire that is part of a circuit• A way to move the coil of wire
Generator• Generator: A device that converts mechanical energy into electrical energy.
• The rotating coil produces an alternating current• Alternating current can be easily transformed
Electric Motors• Electric motors: Convert electrical energy to mechanical energy
• Transformer: A device for increasing or decreasing voltage through electromagnetic induction
• Consist of two different coils of wire around opposite sides of an iron core. • Alternating current through a coil of wire induces a varying magnetic field in the core, ...• ... which in turn will cause a current flow in a secondary coil.
Transformers
Stepup:• Voltage increases• Current decreases• Power stays the same• Less coils on the primary than the secondary
Stepdown:• Voltage decreases• Current increases• Power stays the same• More coils on the primary than the secondary
SteamPowered Generator• Steam drives the turbine, which turns the coil wire in a
magnetic field.
Power Generation
Coal Power Plant1
Nuclear Power Plant2
Geothermal Generator3
MethanePower Plants4
Hydroelectric Power Plant5
Wind and Tidal Generators6
Mechanical Generators• Coal power plants (steam)• Nuclear power plants (steam)• Geothermal power (steam)• Methane power plants (steam)• Hydroelectric power plants (PEgrav)• Wind turbines (KEwind) & Tidal power (KEtide)
Solar Power (nonmechanical)• Electromagnetic energy (Sun) converted into electric power
Power Transmission