Download document

Question: How is lightning similar to getting an electric shock when you
reach for metal door knob?
ELECTRICITY
Electric charges are from protons
+ and electrons
which are negative
which are positive
Static Electricity – accumulation of excess electric charges on an
object
Atoms become charged by gaining or losing electrons.
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
+
like charges repel
attract
CONDUCTORS VS. INSULATORS
Conductors – material in
Insulators – material in which
which electrons move
electrons are not able to move
easily Ex. Metals
easily Ex. wood, plastics, rubber
CHARGING OBJECTS
Charging by Contact
Charging by Induction
- process of transferring
- rearrangement of electrons
charge by touching or
on a neutral object caused by
rubbing
nearby charged objects
Question: What property of electric current allowed Edison’s first
lightbulb to light?
ELECTRIC CURRENT
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
Circuit – a closed path that electric
current follows.
Battery, wires and
voltage difference allows
+
-
current to flow.
BATTERIES
Dry - Cell
Wet - Cell
Chemical reactions occur
Contains two connected
in a moist paste causing
plates made of different
transfer of electrons
metals in conducting sol’n.
Ex. Car Battery
Resisitance – tendency for a material to oppose the flow of
electrons, changing electrical energy into thermal and light
energy.
Making wires thinner, longer or hotter increases resistance
All materials have some electrical resistance measured in
ohms. (symbol )
Ohms Law – current in a circuit equals
voltage difference divided by resistance.
Voltage dff
Current =
Resistance
Question: Why does your home have a circuit breaker or fuse box?
ELECTRICAL CIRCUITS
CIRCUIT SYMBOLS
WIRE
LIGHTBULB
(Conductor)
CLOSED SWITCH
BATTERY
OPEN SWITCH
SERIES CIRCUIT
PARALLEL CIRCUIT
Current has only one loop to
Contains two or more branches
flow through.
for current to flow through.
Examples include:
Examples include:
flashlight, holiday lights
Homes, automobiles
COMPLEX CIRCUIT
A circuit composed of both series and parallel circuits.
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
Questions: Why are magnets so important?
MAGNETISM
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
N
and objects made of
S
magnetic materials
(strongest closed to magnet)
All magnets have a north pole and a south pole.
N
N
S
LIKE POLES REPEL
N
UNLIKE POLES ATTRACT
MAGNETIC MATERIALS
Only few metals, such as iorn, 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.
Questions: How does a stereo speaker use an electromagnet to
Produced sound?
MAGNETISM AND ELECTRICITY
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.
Electromagnets – a temporary magnet made by wrapping a wire
coil carrying a current around an iorn 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
In a simple electric motor, an electromagnet rotates between the
poles of a permanent magnet.
DIRECT AND ALTERNATING CURRENT
Direct Current (DC)
Alternating Current (AC)
- current that flows
- reverses the direction of
In only one direction
the current flow in
through a wire
regular patterns.
Ex. A battery
Ex. Plugging toaster into
Wall outlet