Download Chapter 20 Chapter 20 - Electricity Electricity

Chapter 20 - Electricity
Section 20.2 (Electric Currents)
Section 20.3 (Electric Circuits)
Flow of a Charge
• An electric current is a steady flow of
electric charge.
• Electric charges will flow continuously only
through a closed conducting loop called a
circuit..
circuit
How a Current Flows
• A simple electric circuit
contains a source of
electrical energy, such
as a battery
battery,, and an
electrical conductor,
such as a wire
wire..
• In the figure, a closed
path is formed by wires
connecting a lightbulb
to a battery.
Voltage
• In an electric circuit, a battery increases the
electrical potential energy of electrons.
• Voltage is a measure of how much
electrical potential energy each electron
can gain.
• Voltage is measured in volts (v).
Batteries
• Chemical reactions in batteries
produce an electric field in
batteries which cause electrons to
move from the positive (+) to
negative ((-) terminal.
terminal.
• Batteries contain only a limited
amount of the chemicals needed
to create this electric field.
• When the battery runs out of the
chemicals,, it is “dead”.
chemicals
Resistance
• The measure of how difficult it is for electrons
to flow through a material is called resistance
resistance..
• The unit for resistance is the ohm (Ω
(Ω).
• Insulators generally have much higher
resistance than conductors
conductors..
Ohm’s Law
• Ohm’s Law states:
• Voltage (V) = Current (Amps) * Resistance (Ω
(Ω)
• According to Ohm’s Law, when the voltage in a
circuit increases the current increases
increases..
• Example – Just as water flows faster from a
bucket that is raised higher.
WHAT IS AN ELECTRICAL CIRCUIT?
• Answer:
– A closed path that allows an electrical current
to flow from a power source (i.e., batteries).
Electricity flows from the negative terminal to
the positive terminal.
– If there are any “breaks” in the loop, electricity
will not flow!
– There are two types of circuits we will build:
1. Series
2. Parallel
Series Circuits
If all the parts of an electric current are
connected one after another, the circuit is a
series circuit.
In a series circuit, there is only one path for
the current to take.
Series Circuits - Demonstration
Advantage – Very simple to design and build.
Disadvantage – A burnedburned-out bulb is a break
in the circuit,
circuit, and there is no other path for
the charges to take.
Disadvantage – Light bulbs in the circuit
added.
become dimmer as more bulbs are added.
Why?
Bulbs add more resistance. Ohm’s Law – if
resistance increases, current decreases.
Parallel Circuits
In a parallel circuit, the different parts of the
circuit are on separate branches.
branches.
In a parallel circuit, there are several paths
for current to take.
Parallel Circuits - Demonstration
Disadvantage – More complicated to design
and build.
Advantage – If one bulb goes out, the others
remain lit.
lit.
Advantage – If more bulbs/branches are
dimmer.
added, the bulbs do not become dimmer.
Why?
More paths to take = less resistance = more
current
Build a Series Circuit
Using the two batteries and three bulbs at
your station, build a Series Circuit with the
people at your lab station.
Take turns building the circuit.
circuit.
Build a Parallel Circuit
Using the two batteries and three bulbs at
your station, build a Parallel Circuit with the
people at your lab station.
Take turns building the circuit.