Download Parallel Circuits

Section 14.2
Objectives
Describe how current divides in a
parallel circuit.
 Determine the voltage across and
current through each branch of a parallel
circuit.
 Explain why circuit breakers and fuses
are used in homes.

Parallel Circuits
 A circuit
with more than one path
for the current to flow.
 Each path in the circuit is
sometimes called a branch.
 The current through a branch is
called the branch current.
 In parallel circuits, current splits at 1
or more branch points.
Kirchhoff’s Current Law

All current entering a branch point must
exit again.
 Thus, in a parallel circuit, the current
entering a branch must equal the current
exiting the branch.
Voltage in a parallel circuit

Voltage is the same across each branch
of a parallel circuit.
Both bulbs see 3V from the battery since
each
is connected back to the battery by
wires
without any other electrical devices in
the way.
Advantages
1.
2.
Each device in the circuit has a voltage
drop equal to the full battery voltage.
Each device in the circuit may be turned
off independently without stopping the
current in the other devices in the
circuit.

This is why parallel circuits are used for
most of the wiring in homes.
Current in a parallel circuit
In a parallel circuit, current is determined
using the branch resistance and Ohm’s
law.
 Each branch is independent, so the
current in one branch does not depend
on what happens in other branches.
 Total current is the sum of currents in
each branch.

Calculating current & resistance
In a series circuit, adding a resistor
increases the resistance for the entire
circuit.
 In a parallel circuit, adding a resistor
provides another independent path for
current to flow. As a result, more current
flows for the same resistance. Because
of this, when using Ohm’s law to
calculate, you will see that resistance is
less.

Short Circuits
A parallel path in a circuit with very low
resistance.
 This can happen by accidentally making
a parallel branch with a wire.
 The results could be dangerous as the
low resistance of wires is combined with
very high current, producing large
amounts of heat and possibly starting
fires.

Circuit breakers and fuses

Homes generally have many parallel
circuits, each of which has its’ own fuse
or circuit breaker which stops the flow of
current if the current becomes to high.
Review

Page 326, #’s 1-4