Series and Parallel Circuits

Circuits  Can either be series or parallel.

Lights in a Series

Series 1. Current only takes ONE path Current flows through every part of the circuit If you remove a light bulb or one burns out—all go out! Current is the same at all points

Can use Ohm’s Law to find current using resistance and voltage of the circuit

Current in Series 2. The current is resisted by the resistance of the devices added. This means that as devices are added to a series circuit the total resistance increases.

3. The current in the circuit numerically equal to the voltage supplied by the source divided by the resistance of the circuit. I = V/R

4. Ohm’s Law can be applied separately to each device. This means that the voltage drop across each device depends directly on the its resistance.

5. The total voltage impressed across a series circuit divides among the individual electric devices in the circuit so that the sum of the voltage drops across the individual devices is equal to the total voltage supplied by the source.

Sample Problem #1  Draw a series circuit with two 1.5 V batteries, 3 resistors, and a current of 0.5 A. 1. What is the total voltage of the circuit? 2. What is the resistance of each resistor? 3. What is the voltage drop across each resistor? Label on your circuit.

Lights in Parallel

Parallel Circuits  Has at least one point where current divides  More than one path for current to flow  Paths are also known as branches

Parallel: 1. The total current in the circuit divides among the parallel branches. This means current passes more readily into devices of low resistance, so that the amount of current in each branch is inversely proportional to the resistance of the branch. Ohm’s Law applies to each branch

2. The total current in the circuit equals the sum of the currents in the parallel branches.

3. As the number of parallel branches is increased, the overall resistance of the circuit is decreased. This means the overall resistance of a parallel circuit is less than the resistance on each branch.

Practice problem #2  Draw a parallel circuit with two resistors (one on each branch) and a 12 V battery. 1. What is the voltage through each resistor? 2. What is the current flowing through each branch?

Toll Road—Circuit Analogy

Toll Booth Explanation  Adding toll booths in series increases resistance and slows the current flow.  Adding toll booths in parallel lowers resistance and increases the current flow.

Batteries in Series and Parallel:

 In series—The voltage is increased.  In parallel—No change in voltage; these batteries will last longer!