Circuits Circuits are closed paths that form a loop

Circuits There are three basic parts to a circuit: 1.Energy source (battery, etc) 2.Wires 3.Load (light bulb, radio, etc)

Circuits What does the load do? ~The load changes electrical energy into OTHER forms of energy Ex: thermal, light, mechanical, etc.

Switches ~A switch is used to open and close a circuit ~When a switch is closed, it is “on” ~When a switch is open, it is “off”

Series and Parallel Circuits

Circuits…  Can either be series or parallel.

Series  Current only takes one path for electrons  If there is any break in the circuit, the current will stop flowing

Lights in a Series

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

If one lightbulb goes out… If you remove a light bulb or one burns out—all go out!

If one lightbulb goes out… If your home was wired this way, it would be very difficult! Imagine if your fridge and a lamp were wired in series. When one was off, the other wouldn’t work.

Why Do they exist?  They are helpful!  Example: burglar alarms: if the circuit fails, there is no current. When the current goes out, the alarm sounds.

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

Voltage in Series  This means, as you add light bulbs, they get dimmer. They are sharing the same current.

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:  Your home is wired in parallel. This school is wired in parallel.

Parallel:  Charges in a parallel circuit have more than one path on which they can travel.

Parallel:  Charges in a parallel circuit have more than one path on which they can travel.

Parallel:  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.

Removing a Light Bulb You can connect loads that need different currents to the same parallel circuit. Each branch of the circuit can work by itself.

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

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

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!

One More FINAL Thing:  Two Types of Current:  DC—Direct Current— produced by solar cells and chemical cells (batteries)  Current only flows in one direction.

2 nd type of current:  AC—Alternating Current  Current flows back and forth (alternates)  Found in homes  Generators produce AC current