Before we get started, let’s review:

Describe a Series Circuit

Draw a circuit diagram of a closed series circuit with a 1.5V battery and three light bulbs

What happens if there is a break anywhere in a series circuit?

Why are Christmas lights wired in a series circuit?

A series circuit has only one path for the current so the current is the same at any point in the circuit.

You can use Ohm’s law to calculate the current in a circuit if you know the voltage and resistance.

Adding resistors in a circuit is like adding pinches in a hose. The greater the number of pinches or resistors, the greater the resistance to current (flow).

You can think of adding resistances adding pinches to a hose. Each pinch adds some resistance. The total resistance is the sum of the resistances from each pinch.

To find the total resistance in a series circuit, you add the individual resistances.

A series circuit contains a 12-V battery and three bulbs with resistances of 1Ω, 2 Ω, and 3 Ω. What is the current in the circuit? (First draw a circuit diagram)

A string of 5 lights runs on a 9-V battery. If each bulb has a resistance of 2 Ω, what is the current? (First draw a circuit diagram)

A series circuit operates on a 6-V battery and has two 1 Ω resistors. What is the current? (First draw a circuit diagram)

Voltage Drops and Ohm’s Law -Each separate bulb or resistor in a circuit creates a voltage drop. -As a result, the voltage gets lower after each device that uses power. This is known as the voltage drop.

Voltage drop and Ohm’s law The voltage drop across a resistance is determined by Ohm’s law in the form V = IR. The voltage drop (V) equals the current (I) multiplied by the resistance (R) of the device.

What voltage drop should the Multi-meter read if each bulb has a Resistance of 1 Ohm? Why?

The law of conservation of energy also applies to a circuit. Kirchhoff’s voltage law - the total of all the voltage drops must add up to the battery’s voltage.

To calculate the voltage drop across a resistance, Ohm’s Law (I=V/R) is manipulated to solve for volts, V=IR. This formula must be used for each resistance in a circuit to calculate the voltage drop.

This circuit contains a 9-volt battery, 1-ohm bulb, and a 2-ohm bulb. Calculate the circuit’s total resistance and current. Then find each bulb’s voltage drop.

Parallel Circuits Describe a parallel circuit

Parallel Circuits Draw a parallel circuit with three lightbulbs and two batteries.

Parallel Circuits

Unlike series circuits, parallel circuits contain more than one path for current to flow.

Parallel Circuits Every parallel circuit contains at least one point where the circuit divides, providing multiple paths for the current.

Parallel Circuits The point where the circuit divides is called a juncture or branch point. The paths are called branches. The current through a branch is called the branch current.

Parallel Circuits Because there are multiple branches, the current may not be the same at all points in a parallel circuit. Kirchhoff’s Current Law - At every branch point, the current flowing out must equal the current flowing in.

Parallel Circuits The total current in the circuit is the sum of the currents in all the branches.

Parallel Circuits In a parallel circuit: -the voltage is the same across each branch. -the amount of current in each branch is not necessarily the same. the resistance in each branch determines the current in that branch. Branches with less resistance have larger amounts of current than branches with more resistance.

Voltage and parallel circuits Parallel circuits have two advantages over series circuits. 1. Each device in the circuit has a voltage drop equal to the full battery voltage. 2. Each device in the circuit may be turned off independently without stopping the current in the other devices in the circuit.

Current and parallel circuits Each branch works independently so the total current in a parallel circuit is the sum of the currents in each branch.

Parallel Circuits In series circuits, adding an extra resistance increases the total resistance of the whole circuit. The opposite is true in parallel circuits.

Parallel Circuits Adding resistance in parallel provides another path for current, and more current flows. When more current flows for the same voltage, the total resistance of the circuit must decrease.

Parallel Circuits

A circuit contains a 2-ohm resistor and a 4- ohm resistor in parallel. Calculate the total resistance of the circuit.

Most electrical appliances have a label that lists the power in watts or kilowatts (kW).

The kilowatt is used for large amounts of power. One kilowatt (kW) equals 1,000 watts.

To calculate power in a circuit:

A 12-volt battery is connected in series to two identical light bulbs. The current in the circuit is 3 amps. Calculate the power output of the battery.

VIRP Table Series

VIRP Table Parallel