Download Parallel circuits

Physics
Parallel Circuits
Key Terms
 Parallel
circuits-
Old ones…
 Voltage(v)
 Current (I)
 Resistance (R)
 Series circuit-
Lesson Objective
 All
of the Students will be able to apply
what they know to 3 parallel resistors to
solve 4 out of 5 questions correctly on an
exit ticket.
You will be successful if…
 Make
a checklist of the following items
and check yourself off during the lesson.
 You can determine the difference
between series and parallel circuits using
today’s lab experiment.
 You can “map” and solve for current and
resistance in a circuit with 2 resistors.
 You can “map” a circuit with 3 resistors.
Introduction
 In
your lab today, you took data about
lights in a series and in parallel. What did
your data imply about how much voltage
series lights get as you add more lights?
 What
can you imply about parallel circuits
knowing this?
Review
 In
series circuits, the current was always
the same.
 Voltage decreased with each resistor until
it hit zero at the end.
Diving in


For a Parallel
circuit, Current is
what changes,
and voltage is
the same for all 3
resistors.
Voltage across
all parallel
elements in a
circuit will always
be the same
Fun video or picture
describing subject
Deep

Since in a parallel circuit, they all are
equally close to the battery, the voltage is
the same, but each resistor is different,
and since the voltage they receive is the
same, What does Ohm’s Law say should
happen to the current for each resistor?
 Will
it be the same?
 Why?
Heavy
 Lets
solve one
together.
 Copy
the circuit at
right. See how
resistance and
Voltage are given.
 Note: Current is
divided into 3
separate parts, I1,
I2, and I3.
Heavy
 We
have ohms law
V=IR, so we need
to find ITotal for the
circuit.
 To do this, use
Ohm’s law for
each resistor.
Heavy
 You
should have
gotten
 8 amps for I1
 6 amps for I2,
 12 amps for I3.
Heavy
 Your
total Current
will be???
Heavy
 Now,
what about resistances? Well…
Were going to use the second equation
here to find the total resistance for the
circuit. E
E
E
E
RT

R1

R2

R3
1
1
1
1



RT
R1
R2
R3
GT  G1  G 2  G 3
Lecture exit ticket
 If
V= 120 volts, Itotal = 30 amps, Find Rtotal .
 If R1= 10Ω and R2=15Ω and R3 is unknown
 What value is R3?
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