Transcript Electricity and Magn.. - Caledonia High School

Electricity
and
Magnetism
The Atom

Nucleus
Protons
 Neutrons


Electrons
 Rules
Electric Charge
and Polarity
of Electric Charge

More protons than electrons= positive charge

More electrons than protons= negative charge
 Like=
Repel,
Opposite= Attract
Electric Charge and
Polarity cont…
 *In
electricity, ONLY e- move, not protons!!*
 The
strength of electric force= amount of excess
+ or – charge
 Electric
Field: spot by charged particles where
particles attract or repel
 Electroscope Demo
Electric Fields
 Electric
Field: area around charged particles
where forces of attraction of repulsion exist
Static Electricity
 Methods
of Charging
 Friction- move electrons from 1 spot to
another
 Conduction- transfers electrons through
direct contact
 Induction- charged object forces change of
charge in nearby object without contact
Static Electricity cont…
 Lightning
Particles
move= buildup of charges
 - clouds= electrical charges on earth
Causes electrons to jump from cloud to
earth… lightning!!
Thunder= air expanding due to heat of
lightning
Lightning is attracted to tall objects
Static Electricity cont…
Voltage
The
energy, or push that makes
electrons move
higher voltage = higher energy
each electron carries

Measured
in unit called volt (V)
Flow of Electricity
 Electric
Current- flow of e- through a wire
Current’s symbol is I
Measured in amperes (A)
higher current= higher e-
Flow of Electricity cont…
 Resistance:
opposition to flow of electricity
Symbol is R
Measured in ohms
Poor conductors= high R
ex. Iron
Good conductors= low R
ex. Copper
R=Long and thin wires > short and thick
Any device that gets plugged in is a resistor
(load)
Flow of Electricity cont…
 Ohms
Law: I = V / R
 Direct
Current (DC): electrons flow in the
same direction ex. Batteries
 Alternating
Current (AC): electrons constantly
change the direction the flow ex. Electricity
from power plants
Electricity Circuits
 What
is a Circuit??
Complete, closed path for electric current to
flow
Circuit only works when path is closed
 Parts of a Circuit
A source of ea load (R), device that uses the electricity
Wires to carry the electrons
a switch opens or closes the circuit
Electric Circuits cont…
 Series
Circuit
1 path for current to flow
All parts are connected one after another
Same circuit passes through each resistor
There would be a buildup of charge if
not
Ex. old Christmas lights
Electric Circuits cont…
Parallel
Circuit
Different parts of the circuit are on
separate branches
Several paths of electrons can be
taken
Ex. Newer Christmas light
Electric Power
 Measure
of rate at which electricity does work
or provides energy
 P= V x I
Units: Watts=Volts x Amperes
1 kilowatt = 1000 watts
 E= P x t
Units: Kilowatt- hours= kilowatts x hours
Meter reads kilowatt-hours
Power Distribution Grid
 At
the Power Plant
Generators make 3 phase AD electricity via
generators
Electricity goes through a step-up
transformer
Voltage increased for travel over electric
wires
Voltage is usually stepped up to
between 155000-765,000 volts!!!
Power Distribution Grid cont…
Transmissions
of electricity
High-voltage lines have huge steel
wires
Extras are for phone or support
wires
Electricity travels 300 miles from
power plant
Power Distribution Grid cont…
 Power
Substation
Can do several different things
Have “buses”, split power in different
directions
Decrease voltage by using a step-down
transformer
Power Distribution Grid cont…
 Before
going to the house
Multi phase wires tapped to single phase
Often see 3 wires going to house
Transformer drum steps down 7200 v to
240 v
Underground areas have a green
transformer box above ground
Power Distribution Grid cont…
 At
the house
Electric wires travel watt-hour meter
2 120 volt wires travel to circuit breaker
Splits and is wired to all outlets of the
house
Magnetism
 Magnets
have north and south poles
 Like poles repel, unlike poles attract
 Magnetic Field- where magnetic forces can
act
 Earth
has one, strongest at poles
 Magnetic lines of force define poles
 Electrons in atoms spin, causing magnetic field
Magnetism
 Magnetic
Materials
 Naturally
occur
 Materials that are non-magnetized can become so:
iron, nickel, and cobalt
 Earth
as a Magnet
 Magnetosphere:
region of magnetic field around
 Earth poles: geographical north=magnetic south
Magnetism
 Compasses
 Needle
of a compass is magnetic
 Compass needle points to north pole
 Electromagnetism
 Magnetism
and electricity are inseparable
 Electromagnet: wind wire around an iron core
Has
north and south poles
Magnet’s polarity depends on electric current’s polarity
 Magnetism
and electricity induce each other
Magnetism
 Electromagnets
Electric
wire wrapped around iron core
Temporary
Ex.
magnets, turn on and off
Junkyards, doorbells, telephones
Magnetism
 Electric
Motor
 Electric
energy > mechanical energy (motion)
 Operates idea of reversal of polarity
 Has stationary permanent magnet, rotating
electromagnet, and polarity reversing switch
Magnetism
 Electric
Generator
 Mechanical
energy> electrical energy
 Conductor spins in a magnetic field
Magnetic
lines of force are cut by conductor
Creates electricity, electro magnetic induction
 Power
used everyday comes from generator
Magnetism
 Galvanometer
Detects
electric current
Wire coil connected to electric circuit w/
needle
Current deflects needle towards
direction of current
Magnetism

Galvanometer
Electric Motor

Electric Generator