Transcript Electric Circuits

Electric Circuits
Electric circuit:
a complete path from the
positive terminal to the
negative terminal.
Any path along which electrons
can flow is a circuit.
A gap is usually provided by an
electric switch that can open or
closes the circuit allowing the
electrons to flow or be cut off.
Many circuits have more than
one device that receives electrical
energy.
They can connect one of two
ways……
In series –
they form a single pathway for
the electrons to flow between
terminals of the battery, generator
or wall socket.
Series Circuits
Current through one bulb travels through
the others.
Current has but a single pathway
through the circuit.
This current is resisted by the
resistance of the first device, the
resistance of the second device,
etc……. Total resistance to the
current is the sum of the individual
resistances along the path.
So for series circuits, as more
resistors are added the overall
current within the circuit decreases.
This decrease in current is consistent
with the conclusion that the overall
resistance increases.
The current in the circuit is
numerically equal to the voltage
supplied by the source divided by
the total resistance of the circuit.
This is Ohm’s law.
In Parallel –
they form branches, each of
which is a separate path for the
flow of electrons.
Parallel Circuits
Voltage same across each bulb.
Current same because resistance of each bulb
is the same
Each device connects to the same
two points of the circuit. The
voltage drop is therefore the
same across each device
Total current is divided among the
parallel branches.
Current passes more easily into
devices of low resistance, so the
amount of current in each branch is
inversely proportional to the
resistance in each branch.
(Ohm’s law applies individually to
each branch)
The total current in the circuit equals
the sum of the currents in the parallel
branches
As the number of branches is
increased, Overall resistance is
lowered. This means the overall
resistance of the circuit is less
than the resistance of any one of
the branches.
How to find resistance in a series
and parallel circuit.
Series:
add all the resistance together.
1 Ohm + 1 Ohm = 2 Ohms
In series, the total resistance is
always larger than any individual
resistance.
Parallel:
Use the formula
In parallel circuits, the total
resistance is always smaller than
any individual resistance.
a. Two 3- resistors placed in series
would provide a resistance which is
equivalent to one _____- resistor.
b. Three 3- resistors placed in series
would provide a resistance which is
equivalent to one _____- resistor.
c. Three 5- resistors placed in series
would provide a resistance which is
equivalent to one _____- resistor.
d. Three resistors with resistance
values of 2- , 4- , and 6- are placed
in series. These would provide a
resistance which is equivalent to one
_____- resistor.
e. Three resistors with resistance
values of 5- , 6- , and 7- are placed
in series. These would provide a
resistance which is equivalent to one
_____- resistor.
2. As the number of resistors in a
series circuit increases, the
overall resistance __________
(increases, decreases, remains the same)
and the current in the circuit
__________
(increases, decreases, remains the same).
As more and more resistors are
added in parallel to a circuit, the
equivalent resistance of the
circuit ____________ (increases,
decreases)
and the total current of the circuit
____________ (increases, decreases).