Chapter 7 Parallel Circuits. Chapter 7 Parallel Circuits.

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Chapter 7 Parallel Circuits

Objectives Determine the total resistance of a parallel circuit.
Determine the voltage drops in a parallel circuit. Determine the current values of a parallel circuit. Determine the wattage values of a parallel circuit. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Objectives Apply Ohm’s law to solve for unknown voltage, current, and resistance in a parallel circuit. Apply parallel circuit theory to assist in troubleshooting a parallel circuit. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Parallel Circuit Principles
Two or more resistors connected to the source in parallel © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Parallel Circuit Voltage
ET = E1 = E2 = E3…= EN © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Parallel Circuit Current
Kirchhoff’s current law principles Branch currents Mainline current IT = I1 + I2 + I3…+ IN © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Parallel Circuit Resistance
Total resistance is always less than the smallest resistance Methods to find total resistance Product over sum method Reciprocal method Equal resistances method Graph method © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Product Over the Sum Method
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Reciprocal Method © Goodheart-Willcox Co., Inc.
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Equal Resistances Method
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Graph Method © Goodheart-Willcox Co., Inc.
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Power in a Parallel Circuit
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Review What is a parallel circuit?
A circuit that provides two or more paths for electron flow through a circuit © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review What does the source voltage in a parallel circuit equal?
The same voltage value as any point in the circuit © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review What does Kirchhoff’s current law state?
The algebraic sum of all currents entering any point will equal the sum of all currents leaving that point © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review How does the total resistance compare to the individual resistances in a parallel circuit? Total resistance is less than the smallest resistance © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Applying Ohm’s Law © Goodheart-Willcox Co., Inc.
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Troubleshooting a Parallel Circuit
Compare total resistance reading to the calculated total resistance Take current readings at each resistor © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Using an Ohmmeter to Troubleshoot
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Using an Ammeter to Troubleshoot
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Review Why is checking voltage drops not a practical method for finding a bad component in a parallel circuit? Voltage is the same everywhere in a parallel circuit © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Review How is an ammeter used to troubleshoot?
Current readings across an open switch are taken and then compared to calculated total current © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Branch current Kirchhoff’s current law Mainline current
individual current caused by an individual resistance in a parallel circuit. Kirchhoff’s current law At any junction of conductors in a circuit, the algebraic sum of the currents equals zero. Mainline current Total current in a parallel circuit. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Parallel circuit Reciprocal
Contains two or more paths for electrons supplied by a common voltage source. Reciprocal The reciprocal of a number is one divided by the number. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.