Download Electricity

MAGNETISM/ELECTRICITY
A VERY ENLIGHTENING UNIT!
SHOCKING ISN’T IT?
AREN’T YOU ATTRACTED TO THIS
TOPIC?
• What happened in Magnesia,
Turkey 2000 years ago?
• Greeks discovered a mineral that
attracted things made of iron, they
called it magnetite (after the town it
was found in)
• Magnet: any material that attracts iron
or materials containing iron
• Magnetic pole: 1 of 2 points, such as
the ends of a magnet, that have
opposing magnetic qualities
• Magnetic force: the force of attraction
or repulsion generated by moving or
spinning electric charges
• Magnetic field:
region around a
magnet in which
magnetic forces
can act
• Closer the field
lines, stronger the
magnetic field
• Cause of magnetism: in some metals
moving electrons around atoms can align
to form domains
• Examples of metals that can become arranged into
domains: iron, nickel, cobalt
• So how do
you align
the
domains?
• What would happen to the magnetism
of each piece of this magnet if you cut
it into smaller pieces?
• You would create 2 smaller magnets
with new smaller alignments and poles
• How can you demagnetize a magnet
(in other words, how do you mess up
the aligned domains)?
• Drop it
• Put it near a stronger magnet
• Heat the magnet
(to high temperature)
• Types of magnets:
• Ferromagnets: magnet made of iron, nickel or
cobalt
• Electromagnet: magnet made by running an
electric current through an iron core
• Can you name a very big magnet?
• Hint, it has an enormous iron core of
charged electrons aligning into
domains
• Can you name a very big magnet?
• Ever see an example of the earth’s
polar field?
• What happens when your rub your
feet across a carpet or drag the
blankets across your bed during dry
weather?
• Electric Charge: all matter is made up
of very small particles called protons,
neutrons, and electrons
• These protons (+) and electrons (-) are charged
particles
• Law of electric charges: states that like
charges repel and opposite charges attract



• Electric force: force of attraction or
repulsion on a charged particle that is
due to an electric field
• The closer together the objects, the greater the
electric force
• The greater the charge the greater the electric
force
• Electric field: the space around a
charged object in which another
charged object experiences an electric
force
• Friction: occurs when electrons are
“wiped” from one object to another
• ie: rubbing a balloon on hair causes electrons
to move from hair to balloon
• Electrical conductor: a material in
which charges can move freely
• ie: copper, aluminum, gold…
• Electrical insulator: a material in which
charges cannot move freely
• ie: plastic, rubber, glass, wood, air…
• Static electricity: electric charge at rest;
generally produced by friction or
induction
• Electric discharge: the release of electricity
stored in its source
• Conservation of
charge: when you
charge objects, no
charges are created
or destroyed, just
moved
• Total # of protons and
electrons stays the
same
• Electroscope:
device for detecting
electrical charge
• http://members.shaw.ca/len92/stat
ic.htm
• Electromagnetism: the interaction
between electricity and magnetism
• About all you can do with this is make a
compass needle move
• Solenoid: a coil of wire with an electric
current in it
• Electromagnet: a coil that has an iron
core and that acts as a magnet when
an electric current is in the coil
• It is a solenoid with a piece of iron in the
center
• Electric motor: device that converts
electrical energy into mechanical
energy
• Galvanometer: device with an
electromagnet that measures current
• Electric current: the rate at which charges pass
through a given point
• Measured in amperes (usually called amps or written as
the symbol A or I)
• There are two kinds of current
• Alternating current and direct current
• Hence: AC/DC
• In direct current, the charges always flow in the same
direction
• In alternating current, the charges continually shift
from flowing in one direction to flowing in the reverse
direction
• Voltage: the potential difference between two points
• Really: measure of how much work is needed to move a
charge between two points
• Measured in volts
• Symbol is V
• Think of it this way:
• Resistance: the opposition presented to the current by
a material or device
• Expressed in ohms or the symbol
• Superconductors: conductors that have zero resistance
due to the very cold temperature of a metal
• Photocell: a device that converts light energy into
electrical energy
• Electric power: the rate at which
electrical energy is converted into
other forms of energy
• Power = voltage X current, or P = V x I
• The unit for power is the watt
• Another common unit of power is the
kilowatt (kW)
• = to how many watts?
• How does the electrical company bill you
for the electricity you use each month?
• The amount of electrical energy used
in a home depends on the power of
the electrical devices in the house and
the length of time that those devices
are on
• Electrical energy = power x time
• or E = P x t
• If 2000 W (2 kW) of power are used
for 3 hours then how many kilowatt
hours (kWh) are used?
• Electric circuit: a complete, closed path
through which electric charges flow
• All circuits have 3 basic parts
• Energy source (battery…)
• Wires
• Load (light bulb, radio…)
• A switch is used to open and close a
circuit
• They come in different styles:
• Draw each example below
Open Circuit
Circuit
Closed
• Series: a circuit in which the parts are
joined one after another such that the
current in each part is the same
• Has only 1 pathway for moving charges
• Parallel: a circuit in which the parts are
joined in branches such that the
potential difference across each part is
the same
• Unlike series, each load does not have the
same current
• Unlike series, each bulb (or load) works
independently of each other