Download Electricity

Magnetism
A.
Magnetism – the properties and
interactions of magnets
1.
2.
Interactions between two magnets called
magnetic force increases as magnets
move closer together.
A magnetic field, which exerts the
magnetic force, surrounds a magnet, and
is strongest closest to the magnet.
Magnetism
B.
Magnetic poles – the regions of a
magnet where the magnetic force
exerted by the magnet is strongest
1.
2.
3.
All magnets have a north pole and a south
pole.
Like poles attract. Unlike poles repel.
Earth has magnetic poles.
a.
b.
A compass needle is a small bar magnet that
can freely rotate.
A compass needle always points north.
Magnetism
C.
Magnetic materials – iron, cobalt, and
nickel
1.
2.
The magnetic field created by each atom
exerts a force on nearby atoms.
Magnetic domains – groups of atoms with
aligned magnetic poles
a.
b.
In a magnet, the like poles of all the domains
point in the same direction.
Permanent magnets are made by placing a
magnetic material in a strong magnetic field
forcing a large number of magnetic domains to
line up.
Electricity
Section 1: Electric Charge
A.
Protons have positive electric charge;
electrons have negative electric charge.
1.
2.
3.
In most atoms, the charges of the protons
and electrons cancel each other out and the
atom has no net charge.
Atoms become charged by gaining or losing
electrons.
Static electricity – the accumulation of
excess electric charges on an object.
Section 1: Electric Charge
B.
Electrically charged objects obey the following
rules:
1.
2.
3.
4.
5.
Law of conservation of charge – charge may be
transferred from object to object, but it cannot be
created or destroyed.
Opposite charges attract and like charges repel.
Charges can act on each other even at a distance,
because any charge that is placed in an electric field
will be pushed or pulled by the field.
Electrons move more easily through conductors, like
metals.
Electrons do not move easily through insulators such
as plastic, wood, rubber, and glass.
Section 1: Electric Charge
C.
Transferring electric charge
1.
Charging by contact
a.
b.
2.
The process of transferring charge by touching
or rubbing
Ex: static electricity from your feet rubbing the
carpet
Charging by induction
a.
b.
The rearrangement of electrons on a neutral
object caused by a nearby charged object
Ex: a negatively charged balloon near your
sleeve causes an area of your sleeve to become
positively charged
Section 1: Electric Charge
3.
Static discharge
a.
b.
A transfer of charge through the air
between two objects because of a
buildup of static electricity
Ex: lightning
Grounding – using a conductor to direct
an electric charge into the ground.
D. The presence of electric charges can
be detected by an electroscope.
4.
Discussion Question #1
What do you think happens when you get static
electricity in your hair?
Answer: Some electrons from your hair move
to the sweater or hairbrush, causing the
sweater or hairbrush to have a negative
charge, and your hair to have a positive
charge. Your hair will attracted to the sweater
or hairbrush. Strands of hair that are positively
charged also might repel one another and lifts
straight up in the air.
Section 2: Electric Current
A.
The flow of charges through a wire or
conductor is called electric current.
1.
2.
3.
Current is usually the flow of electrons.
Electric current is measured in amperes (A).
Charges flow from high voltage to low voltage.
a.
b.
4.
A voltage difference is the push that causes charges to
move.
Voltage difference is measured in volts (V).
For charges to flow, the wire must always be
connected in a closed path, or circuit.
Section 2: Electric Current
B.
Sources of electricity:
1.
2.
3.
A dry cell battery produces a voltage of difference
between its zinc container and its carbon
suspension rod, causing current to flow between
them.
A wet cell battery contains two connected plates
made of different metals ina conducting solution.
Wall sockets have a voltage difference across the
two holes of an electrical outlet, and a generator at
a power plant provides this voltage difference.
Section 2: Electric Current
C.
Resistance – the tendency for a material to
oppose the flow of electrons, changing
electrical energy into thermal energy and
light.
1.
2.
3.
D.
All materials have some electrical resistance.
Resistance is measured in ohms (W).
Making wires thinner, longer, or hotter increases
the resistance.
Ohm’s law – the current in a circuit equals the
voltage difference divided by the resistance.
Discussion Question #2
What property of electric current causes
lightbulbs to give light?
Answer: Resistance. As electrons flow
through the filament, the filament resists
flow and changes electrical energy into
thermal energy and light.
Section 3: Electrical Circuits
A.
Circuits rely on generators at power plants
to produce a voltage difference across the
outlet, causing the charge to move when
the circuit is complete.
1.
Series circuit – the current has only one loop
to flow through
a.
b.
c.
The parts of a series circuit are wired one after
another, so the amount of current is the same
through every part.
Open circuit – if any part of the series circuit is
disconnected, no current flows through the circuit
Ex: strings of holiday lights
Section 3: Electrical Circuits
2.
Parallel Circuit – contains two or more
branches for current to move through
a.
b.
Individual parts can be turned off without
affecting the entire circuit.
Ex: the electrical system in a house.
Section 3: Electrical Circuits
B.
Household circuits use parallel circuits
connected in a logical network.
1.
2.
3.
Each branch receives the standard voltage
difference from the electric company.
Electrical energy enters your home at the circuit
breaker or fuse box and branches out to wall
sockets, major appliances, and lights.
Guards against overheating electric wires:
a.
b.
Electric fuse – contains a small piece of metal that melts if
the current becomes too high, opening the circuit and
stopping the flow of current.
Circuit breaker – contains a small piece of metal that bends
when it gets hot, opening the circuit and stopping the flow of
current.
Section 3: Electrical Circuits
C.
Electrical energy is easily converted to
mechanical, thermal, or light energy.
1.
Electrical power – the rate at which electrical energy
is converted to another form of energy
a.
b.
c.
2.
Electrical power is expressed in watts (W).
Power = current x voltage difference
P (watts) = I (amperes) x V (volts)
To calculate the amount of energy an appliance
uses:
a.
b.
c.
The unit of electrical energy is the kilowatt-hour, which
equals 1000 watts of power used for one hour.
Energy = power x time
E (kWh) = P (kW) x t (h)
Discussion Question #3
Does your home have a fuse box or a circuit
breaker? Why is it there? How does it work?
Answer: It is there to make sure the electrical
wires in our home do not get too hot and start
fires. If the wires get too hot, they melt the
piece of metal in the fuse or bend the piece of
metal in the circuit. This opens the circuit and
stops the flow of current. If we have a fuse
box, we have to replace the melted fuse with a
new one. If we have a circuit breaker, we only
need to unplug some appliances and then flip
the switch.