BEX 100 BASIC ELECTRICITY FOR NON MAJORS
LECTURE GUIDE – UNIT 7
Instructor: Jerry Brown
Reference: Delmar’s Standard Textbook of Electricity, Second Edition
PARALLEL CIRCUITS
Objectives
At the completion of the lesson, the student should be able to:
1. Understand the Characteristics of parallel circuits
2. State the three rules for solving electrical values of parallel circuits
3. Compute values of voltage, current, resistance and power for parallel
circuits using the three rules and Ohm’s Law
4. Explain the operation of a current divider circuit
5. Calculate current values using the current divider formula
INTRODUCTION
Examples of parallel flow in fluid systems:
Transfer to Holding Tank(s)
Divided Parallel Hydraulic Circuit
Two (Parallel) discharges from the same tank
Typical house parallel circuit
Parallel Circuit Definition
A parallel circuit has more than one path for current flow
Voltage across any branch equals the applied (supply) voltage
Total resistance is the reciprocal sum of reciprocals of each branch and
is always less than the resistance of the smallest branch
Parallel Circuit Values
Total resistance is always less than the resistance
1
Finding the Total Resistance of a parallel circuit when all resistors have the
same value
Finding the Total Resistance of a parallel circuit by dividing the product of
two resistors by their sum
Finding the total resistance of the last two branches
2
Find the Total Resistance of the circuit (Combine above with last branch)
Finding the Total Resistance by the reciprocal method
1/RT
= 1/R1
+ 1/R2
+ 1/R3
Parallel Circuit, Example #1
3
The Voltage is the same across all branches of a parallel circuit
The total power in a parallel circuit is the sum of the power of the individual
branches
Parallel Circuit, Example #2
The voltage is the same across all branches of a parallel circuit
4
Parallel Circuit Rules
Rule #1 – The voltage across all branches is the same and equals the
applied voltage
Rule #2 – The current divides through each branch and the Total Current
the sum of the currents through all of the branches
Rule #3 – The total resistance is the reciprocal sum of the reciprocals of
each individual branch
SUMMARY
1. A parallel circuit is characterized by the fact that it has more than one
path for current flow.
2. Three rules for solving parallel circuits are:
a. The total current is the sum of the currents through all of the
branches of the circuit.
b. The voltage across any branch of the circuit is the same as the
total voltage.
c. The total resistance is the reciprocal of the sum of the reciprocals
of each individual branch.
3. Circuits in homes are connected in parallel
4. The total power in a parallel circuit is equal to the sum of the power
dissipation of the individual branches
5. Parallel circuits are current dividers
6. The current flowing through each branch of a parallel circuit can be
computed when the total resistance and total current are known
7. The amount of current flow through each branch of a parallel circuit is
inversely proportional to its resistance (Ohm’s Law)
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REVIEW
1. Give a definition of a parallel circuit.
2. State three rules for solving parallel circuits.
a.
b.
c.
3. Why are circuits in homes connected in parallel?
4. What circuits are connected in parallel in cars?
5. Why are parallel circuits called current dividers?
6. How is power dissipated in a parallel circuit?
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