Transcript What is Electricity?

Chapter 16:Electricity
Section 1 – What is Electricity?
• Definition: electricity – is the FLOW of
electrical charges from am area of high
electrical potential energy to one of lower
potential energy.
– Electricity is caused by unbalanced electric
charge.
eeee- e- e
e- e
e- ee- e-
• Definition: electric charge - a property of
matter based on the number of electrons on
an object.
– Objects can gain or lose electrons to change their
charge.
Benjamin Franklin
identified the property of electric charge and
gave it the positive/negative name!
• Electric charge can be positive, negative, or neutral.
Negative: more – than +
Neutral: Same number of + and –
+ +- +
+ +-
+ --+
-+ -
Positive: more + than –
+
+ +
- - -
• A type of matter has an overall electric
charge if the number of protons does not
equal the number of electrons.
• Matter can become charged by other
types of matter… When there is friction
between two objects electrons can be
transferred from one object to the other.
Some materials allow charges to flow, while other
objects stop the flow of electrical charges.
• Definition: electrical conductor – a material
that allows charges to move freely.
• Definition – electrical insulator – a material
that does not transfer charges easily.
 CONDUCTOR
NSULATOR 
Insulators / Conductors
• Some conductors:
– All Metals
– Salt Solutions (electrolytes)
– Silver is the best metal conductor!
• Some Insulators:
– Wood / Cloth
– Glass ; Plastic; Rubber; Air
Electric force is a property that is responsible for
most of the common forces that we experience, like
friction.
– Definition: electric force- Is a universal force that
exists between any two charged objects.
The strength of the force is related to the electric
charge: the stronger the charge, the stronger the
force. The strength of the force drops rapidly with
increasing distance.
• Electric force exists as an invisible field around
charged objects.
• It causes:
•Opposite charges attract.
•Like Charges repel.
+
A positive electric
field pushes
outward.
-
A negative electric
field pulls inward.
That explains why opposites attract!
+

+
The arrows are pointing in the same direction…
-


+
-
• Definition: static electricity – a build up non-moving
electric charges on an object.
– Static electricity is often produced by friction!
– Friction causes electrons to stick to some materials…
• As more and more electrons build up, the static charge
increases.
Static Electricity
• Static discharge occurs when the static electricity
flows away from its source.
• Definition: electric induction – the process by which
a charged object causes another object to become
charged.
– Example: combing your hair causes static charge to form
on the comb.
– The comb can then be used to charge pieces of paper.
Chapter 16: Electricity
Section 2 – Electric Current
When electrons begin moving, they form a
stream of electricity, called a current.
• Definition: electrical current – a measure of the
# of electrons moving through a conductor.
Current is measured in amps (A).
MORE ELECTRONS = MORE CURRENT
Electricity is often discussed in terms of voltage.
– Do you have any idea what voltage is?
• Definition: voltage – is the change in the
charged particle’s potential energy divided by
its charge. In other words the amount of push
a charged particle needs to move.
– Voltage measures the amount of work that must
be done to move a charge.
• Voltage has units of volts, V.
Yes, work has to be done to move electrons!
– The voltage on a battery, for instance, tells how
much work that battery can do.
Electric Current
• Do you think a 1.5 volt battery can power a car?
• Of course not!!
• The car needs a 12 volt battery.
• The 1.5 v battery doesn’t
produce enough force to
move all of the electrons
needed to run the electronics.
Speaking of batteries…
• Definition: battery – a device able to convert
chemical energy into electrical energy.
– Batteries DO NOT store electricity!
So, how do batteries work?
– Each battery contains an electrolyte (an acid), a
cathode, and an anode. A chemical reaction
releases electrons from one end to the other
which creates a circuit to the other end.
• Definition: cathode – the + end of a battery.
• Definition: anode – the - end of a battery.
• A neg. charge
collects on the
anode.
• The charge flows
to the cathode
when connected
by a wire.
• The flow is the
circuit created
between the two
ends.
• Each of the batteries below have the SAME
voltage, but are used in different electronics.
• What is different about them?
THEY PUSH DIFFERENT AMOUNTS OF
ELECTRONS…WITH THE SAME AMOUNT
OF FORCE.
• Its kinda like…
Moving a small
amt. of water at 10
mph.
Think AAA battery…
Moving lots of
water at at 10
mph.
Think D-Cell battery…
The water is moving at the same speed, but different
amounts of water are being moved!
The amount of water represents current (amps)…in case you didn’t
figure that out yet.
When a current cannot flow through a material
easily, it is encountering resistance.
• Definition: resistance – opposition to the flow
of electric current.
– In other words, resistance slows down or stops
the flow of electrons.
– Electric insulators cause almost 100%
resistance.
• Enough resistance to stop the flow of electricity.
Electric Current
• Resistance is a form of friction.
– Resistance can cause some electric energy to be
converted into thermal energy…
Electric stoves work by
using that fact!
Electricity flows through
The coil, which causes
resistance.
Chapter 16:Electricity
Section 3 – Circuits
What is a circuit?
• When you flip the light switch, the light comes
on…obviously.
• What does the switch have to do with it??
– The switch on the wall is part of a circuit.
– When it is switched to the ON position, it allows
electric current to flow into the light bulb.
Circuits
– Definition: circuit – a set of components that
allow one or more complete paths for electric
current to flow.
– Any time electricity is flowing, a circuit is present.
• Whenever current flows, it encounters resistance.
– We can measure this resistance with:
• The Resistance Equation (Ohm’s Law):
– Resistance = Voltage/Current (R = V/I)
– Resistance is measured in Ohms (Ω).ethe
– The resistance of a circuit is affected by the
component that make up the circuit.
• For example, the wires that are in the circuit :
Longer wires = more resistance
Smaller diameter wires = more resistance
High temp wire= more resistance
Insulators= more resistance
Circuits
• When electricity is able to flow freely through a
circuit, that circuit “closed”.
• Incomplete circuits will not allow electricity to flow
freely.
– They are called “open” circuits.
Types of Circuits
– Definition: series circuit – a circuit that forms a
single pathway.
– Electricity can only flow one way in a series
circuit.
Types of Circuits
• Definition: parallel circuit – a circuit that forms
multiple pathways for electricity.
– Parallel circuits can have a piece removed from
them and still allow electricity to flow in another
part of the circuit.
Circuit Components
• Circuits consist of many different things.
• The most common components of a circuit are:
–
–
–
–
–
Power Supplies
Wires
Resistors
Bulbs
Switches
• Definition: resistor – a device that blocks SOME (not
all) electric current in a circuit.
• Appliances like TV’s, lights, computers…these are all resistors.
Electric Current in wires….
• Electric resistance explains why electronics
get hot as they run.
• Even conductors cause some resistance.
• As a wire gets thicker, there is less resistance.
Lots of Resistance
Some Resistance
Little resistance
Electric Current in wires….
• As a wire gets shorter, there is less resistance.
Lots of Resistance
Some Resistance
Little resistance
Electric Current in wires….
• As a wire gets thicker it can carry more
electric current.
Basic Circuit Symbols (copy these to notes!)
Resistor
Wire
Battery or
Power Source
Bulb
Open Switch
Closed Switch