Series and Parallel Circuits

Circuits Can either be series or parallel.

Series Current only takes one path for electrons Current flows through every part of the circuit

Lights in a Series

Series If you add a resistor (like another light): Total resistance goes UP since all the current must go through each resistor.

Adding Resistors to Series: Current in the circuit will go DOWN (lights will dim) If you remove a light bulb or one burns out—all go out!

Current in Series Current is the same at all points Use Ohm’s Law to find current using resistance and voltage

Calculating Current Example:

Voltage is reduced by each resistance – voltage drop Voltage in Series Voltage is reduced by each resistance – voltage drop

Calculating Voltage Example

Resistance in Series Add up all resistors to get total Total resistance will go up because all of the current must go through each resistor.

Calculating Resistance Example:

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

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

Lights in Parallel

Parallel: Total resistance goes down If you add a resistor: Total resistance goes down Total current goes up when you add another path

Removing a Light Bulb If you remove a light bulb or one burns out, the others stay on because the circuit is still closed.

Current in Parallel Current flows into a branching point, the same total current must flow out again Current depends on resistance in each branch

Calculating Current Example:

Voltage in Parallel Voltage is the same across each branch – because each branch is on the same wire

Calculating Voltage Example:

Resistance in Parallel Calculate current in each branch based on resistance in each branch by using Ohm’s Law

Calculating Resistance Example:

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