Download Comparing Electric and Gravitational Forces

5. Comparing Electric and Gravitational Forces
a. Electric force stronger than gravity
b. All atoms are held together by electric
forces greater than the gravitational forces between
the same particles. If only there was a way to
harness the E contained in atoms. Any ideas?
c. Most objects are electrically neutral. No
noticeable electric force.
B. Conductors and Insulators
1. Conductors
a. Material in which electrons are able to
move about easily.
b. Metals – atoms in metals have
electrons that are able to move easily. Copper is
the best.
2. Insulators
a. A material in which electrons are not
able to move easily.
b. Electrons are held tightly. Plastic, wood,
glass.
C. Charging Objects
a. Rubbing 2 materials together may
result in a transfer of electrons. One is left with a
positive charge and the other a negative. Charging
by contact – sometimes called contact by friction.
1.
Charging at a Distance
a. Charging electrical forces act at a
distance charged objects brought near a neutral will
cause electrons to rearrange their positions on the
neutral object.
b. Charging by induction (not touching) –
rearrangement of electrons on a neutral object
caused by a nearby charged object.
2.
Lightning
a. Lightning is a large static charge.
b. Cloud generates charges. As they swirl
areas of positive and negative charges form.
Eventually enough charge builds up to cause a
discharge between the cloud and the ground. The
collision between the charge and the atoms and
molecules in the air cause light to emit.
3. Thunder
a. Sound waves are also created. The
electrical energy in lightning rips electrons off the
atoms as it passes creating sound.
4.
Grounding
a. Electronics can be harmed by large static
discharges. Grounding provides a path for the
charges to go directly to the earth. Earth is neutral
and a conductor. It will suck up charge. Lightning
rods on top of tall buildings.
D.
Detecting Electric Charge
a. Electroscope used to detect electric
charge.
Section Review – Vocab self-check ?s 2 and 3
Section 2 Electric Current
A. Current and Voltage Difference
a. Electric current – net movement of
electric charges in a single direction.
Usually in a wire. Slide for electric current.
b. Measured in amperes.
1. Voltage Difference
1. Electron moving in current is
similar to ball bouncing down
stairs.
2. Flow of current is due to electric
force.
3. Electric charge flows from high
voltage to low voltage.
4. Voltage difference – the force
that causes electric charges to
flow.
5. Measured in volts.
2. Electric Circuits
1. Electric Circuit – closed path that
electric current follows.
B.Batteries
a. Voltage difference needs to be
maintained in circuit in order to keep
electric current flowing.
b. Current flows as long as there is
1. Closed path
2. Path connects one battery terminal
to the other.
1. Dry Cell Batteries
a. Cell consists of 2 electrodes
surrounded by a material
called an electrolyte.
Electrolyte allows charges to
move from electrode to
electrode.
b. Dry cell because electrolyte is
moist paste not a liquid.
2. Wet Cell Batteries
a. 2 connected plates made of
different metals or metallic
compounds in a conducting
solution.
b. Several wet cells connected
together.
3. Lead-Acid Batteries
a. Car batteries.
b. 6 wet cells in a sulfuric acid
solution.
c. Chemical reaction that
provides a voltage difference.
d. Voltage difference at wall
sockets. Usually higher than a
battery.
C. Resistance
a. Filament – thin wire inside a light bulb.
Electrons flow through filament they
bump into metal atoms.
b. This bumping causes some of the
electrons to turn into thermal E.
eventually there is enough thermal E for
the filament to glow. It is this glow that
lights the room (and Haleys smile)
1. Resisting the Flow of Current
1. Electric current loses E as it flows.
The filament resists the flow of
electrons.
2. Resistance – tendency for a
material to oppose the flow of
electrons, changing electrical E
into thermal and light E.
3. Almost all materials have some
electrical resistance.
4. Resistance is measured in ohms.
5. Copper has a low resistance.
2. Temperature length and thickness
1. Resistance increases with:
1. temperature.
2. length of wire.
3. thinness of wire.
4. Hallway example
D. The Current in a Simple Circuit
a. Contains
1. Voltage difference (battery)
2. Device (lightbulb)
3. Conductors (wires)
b. When wires are connected to either end
of the battery in a closed circuit current
will flow.
1. Ohms Law
1. Relationship between voltage
difference, current, and
resistance is Ohms law.
2. Current in a circuit is equal to the
voltage difference divided by
resistance.
Section Review – Vocab self-check 1,3
Section 3 Electrical E
A.
Series and Parallel Circuits
a. Voltage difference – battery, outlet
b. Devices that use E – lights,
c. Conductors – wires that close circuit.
1. Series Circuits
a. Only 1 loop for current to flow through.
2. open circuits
a. Parts of a series circuit are wired one after
another the amount of current is the same
through every part.
b. When any part is disconnected no current
flows through the circuit. This is open
circuit. Bad if you to play minecraft!
3. Parallel Circuits
a. Parallel circuits contain 2 or more branches
for the current to move though.
b. All branches connect the same two points in
circuit the voltage difference is the same in
each branch.
c. Advantages – if one path is opened current
continues to flow through other branches.
B.Household Circuits
a. Wiring in house is parallel circuits.
b. 120 volts coming out of standard American
socket.
c. Circuit breaker is electrical headquarters of
your house. Parallel circuits originate here
and flow electrons to other parts of your
house.
d. Distribute electricity to avoid making wires
too hot. Heat will melt insulation and cause
a fire.
1. Fuses
a. Piece a metal that melts if circuit gets too
hot. Once it melts the circuit is open and
current stops.
b. Before replacing the fuse unplug some
items.
c. Overheating is usually caused by too many
appliances in the circuit.
2. Circuit Breaker
a. A piece of metal than bends when
overheated. Once it bends it flicks off the
circuit to the off position. Once off no
electrons are flowing.
b. Before switching the circuit back on remove
some appliances from the circuit.
C. Electric Power
a. Electric power – rate at which electrical E is
converted to another form of E.
b. We can convert electrical E into – light,
heat, and mechanical E.
c. Appliances that use heat (microwave/hair
dryer) need more electrical E.
1. Calculating Electric Power
a. Electric power depends on voltage
difference and current.
b. Unit for power is watt. Watt is small unit
so power is often expressed as Kilowatts.
2. Electrical E
a. Electric power costs money. Electric
company charges by amount of electrical
energy NOT electrical power.
3. Cost of Using Electrical E
a. Cost of using an appliance can be
calculated by multiplying the electrical E
used by the amount the power company
charges for each kilowatt.
Section Review
Vocab questions 1 - 2