Download Science 9 Electricity Notes

Science 9 Electricity Notes
Name:_____________Block:_____
Ch_9_Review:
Static Electricity:
Review of Chapter 9 (Pages 274-299)
 The buildup of electrical charge as the result of some
types of materials being rubbed together. Ex: getting
a shock by touching something after walking on a rug,
your hair sticking up after being rubbed with a
balloon.

Some materials become electrically charged when rubbed
with other materials. This occurs due to positive or
negative charges that cause an electric force.
Electric discharge is the removal of an electric charge
from an object.
When you walk across a rug, you gain an electric charge.
Later, when you touch something and feel a shock, you
become discharged.
Some other examples of electric discharge are: lightening,
electric shock, and wearing out a battery.
An electric force is the attraction or repulsion between
objects or particles that have an electric charge.
Types of charge:
There are two types of charge. + (positive) and (negative). An object with no charge is said to be neutral.
Repulsion: When two objects having the same charge are
brought close together, they push each other away (repel).
Attraction: When two or more objects having opposite
charges are brought
together, they are attracted to each other.
Attraction occurs when one object loses electrons to the
other. For example, when two objects are rubbed together,
one object may have a stronger attraction for electrons
than the other object has. This object will take electrons
from the other object. The object with the most electrons
becomes negatively charged and the other object which has a
shortage of electrons becomes positively charged.
Laws of electric charges:
1. Opposite charges attract each other.
2. Similar (like) charges repel each other.
3. Charged objects attract neutral objects.
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Science 9
Chapter 10
Current Electricity:
(Pages 302-333)
In static electricity, the electricity produced by rubbing
materials together did not move. (Static= at rest). Once
the electrons were transferred from one object to another,
they were at rest.
In current electricity, the electrons do not remain at
rest, but move from one place to another.
Current Electricity: The continuous movement of charged
particles through a
conductor.
Conductor: A material that allows electricity to pass
through it easily.
Conduction: A transfer of energy through a material by the
direct collision of particles.
Energy from another source is needed to produce energy in
the form of an electric current. Some common energy sources
are batteries and generators.
Detecting Current
We can find out if there is a current in a wire by using a
“current detector.” A detector allows us to compare the
strengths of different currents.
Ampere: The number of electrons moving past a point in one
second. It is the unit for measuring electric current.
Ammeter: A device used to measure strong electric currents
(> 1 Amp).
Galvanometer: A device used to measure weak electric
currents (usually less than 1 mA).
Electric (Chemical) Cells:
Cell: A device that converts chemical energy into electric
energy.
Chemical cell: a chemical device for producing electric
current.
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Battery: Two or more cells joined together to produce an
electric current.
Volt:
A unit used to measure the energy of charges delivered by a
cell. The more voltage a cell has, the more energy is
supplied to the electrons that leave the cell to produce an
electric current.
Voltmeter: A device used to measure the voltage produced in
an electric charge.
Electrode: Part of an electric cell that allows electrons
to enter or leave the cell; it is usually made of a metal
or of carbon.
Electrolyte:
A solution that conducts electricity (can be
found in a cell).
The wet cell: This is a cell made from an electrolyte
liquid and 2 electrodes placed in a beaker or similar
container
An electrolyte solution is one that will conduct
electricity. Eg. Acids, salt water, bases.
The two electrodes MUST be different conducting materials,
eg. Carbon
and Zinc or else the wet cell will not work.
The amount of electrical current a wet cell produces
depends on:
1) The concentration of the electrolyte solution. Eg,
Strong acid will conduct more electricity than weak acid.
2) The types of electrodes used.
Electric cell structure and operation
All cells have 2 parts in common
1) They all have electrodes, each one made from a different
metal
2) They all have their electrodes separated with an
electrolyte solution between them
How cells generate an electric current:
(How they work)
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A chemical reaction between the chemicals in the
electrolyte and the zinc electrode causes extra electrons
to build up on the zinc electrode.
At the same time, the carbon electrode loses electrons. The
zinc electrode has more electrons than the carbon
electrode. So, we say the carbon electrode is + and the
zinc one is negative.
If a connecting wire is placed between the + and terminals, the imbalance of electrons causes a flow of
electrons from the + carbon terminal to the – zinc
terminal.
Resistance:
A measure of how much a material resists the passing of
electricity through it.
Poor conductors resist electric flow. Because of this, they
give off heat (and may even catch on fire).
Wire diameter (thickness) and wire length can affect
resistance.
The thicker the wire, the less the resistance.
The longer the wire, the greater the resistance.
Resistor:
A device made from a material that resists the flow of
electricity.
The greater the resistance of a material, the greater the
amount of energy the electrons give up as they pass through
the resistor.
Eg: An ordinary light bulb.
The filament that glows to give us light is made from a
very resistant metal called tungsten. As electrical current
meets the tungsten filament, it tries to “push through”.
The tungsten resists the flow, so it heats up. This causes
it to glow, giving off light.
Heating elements of stove, toasters, kettles, are all
resistors. Televisions and other appliances contain
resistors.
Circuits; Series and Parallel:
(Section 10.1_Page 302).
Load: An electric device
Source: A cell (or battery)
Conductor: The wire
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Series vs. Parallel Circuits:
(Section 10.2_Page 307).
Series Circuit: One in which the electrons flow through
each device along a single connecting path. (Eg: The
removal of one bulb in the circuit causes all the rest to
go out)
Diagram of a Series Circuit:
Figure 3; Page 307
Parallel Circuit: An electric circuit that provides
alternate conducting paths for an electric current. (Eg:
Remove one bulb, the others stay lit).
Analogy: Block a river with a dam; water stops downstream
unless there are other smaller rivers it can enter to go
around the dam.
Switch: A device used to open or close an electric current.
Switch=open-- power off
Switch=closed– power on
Diagram of a parallel circuit:
Circuit symbols:
Figure 3; Page 307
Page 536; Table 9
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Factors which affect the quantity of electric current in
series and parallel
circuits:
1) The source voltage:
The higher the source voltage, the greater the current
flowing
2) Resistance of the conductor:
The lower the resistance, the greater the flow (quantity)
of current.
The higher the resistance, the lower the current flow will
be.
3) The diameter (thickness) of the wire conductor:
The thinner the wire, the less current it can conduct.
The thicker the wire, the more current it can conduct
4) The distance of the circuit:
Resistance will increase with distance so current will
decrease the further the load is from the source.
5) The type of material the conductor is made from:
Copper is a good conductor. So are carbon, gold, and
silver. Gold is
probably the best one but it is far too expensive to use
for everyday wiring.
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