Transcript Electricity - hinds.k12.ms.us

ELECTRICITY
AND MAGNETISM
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Electricity
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Electric charges are from protons which are
positive + and electrons which are negative
Static Electricity – accumulation of excess
electric charges on an object
Atoms become charged by gaining or losing
electrons.
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-
.
Law of Conservation of Charge – electric charges
can be transferred from object to object, but it
cannot be created or destroyed.
Positive and negative charges exert forces on each
other.
+
-
opposite charges
attract
+
+
-
-
like charges repel
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CONDUCTORS VS. INSULATORS
Conductors – material in
which electrons move easily
Ex. Metals
Insulators – material in which
electrons are not able to move easily
Ex. wood, plastics, rubber
Charging Objects
Charging by Contact process of transferring
charge by touching or
rubbing
Charging by Induction rearrangement of electrons on
a neutral object caused by
nearby charged objects
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Electric Current
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Electric Current – net movement of
electric charges in a single direction
through a wire or conductor.
Voltage Difference – force that causes
electric charges to flow; charges flow
from high voltage low voltage
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Circuit – a closed path that electric current follows.
Battery, wires, and
voltage difference
allows current to
flow.
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BATTERIES
Dry Cell
Chemical reactions occur in a
moist paste causing transfer of
electrons
Wet Cell
Contains two connected plates
made of different metals in
conducting solution.
Ex. Car Battery
Resistance – tendency for a material to oppose the flow of
electrons, changing electrical energy into thermal and light
energy.
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Making wires thinner, longer or hotter increases resistance
All materials have some electrical resistance measured in ohms.
(Ω)
Ohms Law – current in a circuit equals voltage difference divided
by resistance.
Voltage diff
Current =
Resistance
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Electrical Circuits
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Electrical energy enters your home at the circuit breaker or
fuse box and branches out to appliances, wall socket and
lights.
Circuit breakers – small piece of metal that
bends when it gets hot, opening circuit and
stopping current flow.
Electronic fuse - small piece of metal that
melts if current becomes to high, opening
circuit
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Magnetism
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Magnetism – refers to the properties and interactions of
magnets in which there is a force of attraction or
repulsion between like or unlike poles.
Strength of force between two magnets depends on the
distance between them.
Magnetic field – exerts a force on
other magnets and objects made of
magnetic materials (strongest closed
to magnet)
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All magnets have a north pole and a south pole.
LIKE POLES REPEL
UNLIKE POLES ATTRACT
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MAGNETIC MATERIALS
Only few metals, such as iron, cobalt, and nickel
are attracted to magnets or can be made into
permanent magnets.
Magnetic domains – group of atoms with aligned
magnetic poles (too small to be seen with eye)
Permanent magnets are made by placing a
magnetic material in a strong magnetic field,
forcing magnetic domains to line up.
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Magnetism
And
Electricity
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When electric current flows through a wire, a
magnetic field forms around the wire.
ELECTRON
FLOW
WIRE
Strength of magnetic field depends on the amount
of current flowing in the wire.
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Electromagnets – a temporary
magnet made by wrapping a wire
coil carrying a current around an
iron core.
Increases strength of the magnetic field by adding more
turns to wire coil (solenoid) or increasing the current
passing through the wire
Electric motor – a device that
changes electrical energy into
mechanical energy
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In a simple electric motor, an electromagnet rotates
between the poles of a permanent magnet.
DIRECT AND ALTERNATING CURRENT
Direct Current (DC) – current
that flows in only one direction
through a wire
Ex. A battery
Alternating Current (AC) - reverses
the direction of the current flow in
regular patterns.
Ex. Plugging toaster into Wall
outlet
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