Electrical Circuits

A circuit is a closed loop in which electricity flows. The main parts of a circuit: Switch – “Completes” or “breaks” the circuit. Load or Resistor (device) – The “purpose” of the circuit. Voltage Source or Energy Source (battery) – pushes the electricity around the circuit. Conductor (wire) – connects each part of the circuit.

1. The Switch Where is the switch in this circuit? Is there one? A Switch controls the circuit by either completing the loop or breaking the loop. When a circuit is completed or working we call it closed. When it is not working we call it an open circuit. The difference is made because electrons can either flow in a continuous complete path or not - depending on the switch! Where is the switch in this circuit? Is there one?

Confused? 2. The Voltage Source The voltage source is what makes the electrons move through a circuit. If electrons don’t move, then there is no electricity! How do you force electrons to flow? Voltage – A measure of the “difference in potential” in a circuit. Think of this like electrical pressure – the larger the difference, the more electrons want to move. Confused? …….Sometimes it helps to relate this principle to something we already understand……..

Which picture shows the biggest difference in air pressure? Because there is a larger difference between the outside and inside pressure of the balloon, the air wants to get out really bad. Untie the knot or pop it and you’ll see!

Which picture shows the biggest difference in water pressure? In this picture, there is a greater difference between the pressure on the top of the tank and the pressure bottom on the tank. When the 20 gallons spigot on the bottom is opened, both tanks will eventually drain the same amount -20 gallons, but the top tank’s water will exit with much more force and faster! 20 gallons If this where electricity, we would say that each has the same amperage but the top tank has a higher voltage.

A Battery creates this difference in “electrical pressure” called voltage through chemistry. Electrons want to travel from the negative (-) terminal of a battery to the positive (+). A higher voltage battery has a larger difference in potential (pressure) between these two terminals. Thus, electrons are pushed along with much more speed than in a lower voltage battery. With the right metals and chemicals, you too can make a battery!

3. The Conductor The conductor or wire in a circuit allows electrons to travel through it. This is what connects the negative terminal (-) to the positive terminal (+) on the voltage source (battery). However, you always want something in between – or you will create a short circuit shown above (dangerous). Plus, what point would the circuit shown possibly serve? The conductor can connect many various parts of a circuit while still making sure that the electricity can continuously flow back to the voltage source.

4. The Load This can come in many forms: The Load is the portion of the circuit that you “need” the electricity for in the first place. This device is also considered a resistor – allowing some electricity to pass through (to complete the circuit) but also slowing some of it down to use up and convert to another form of energy. This can come in many forms: Motor Bell Light Buzzer Heating Element

There are two main ways to introduce 2 or more loads into a circuit. Series Circuit - Loads are placed end to end in one path along the circuit. -simplest to build -loads “share” the same current -Overall Resistance increases and voltage drops as more loads are added. -If one load “goes out”, the others often do too. Parallel Circuit – Each load is placed on it’s own “branch” so current has more than one path it can travel on. -Voltage and Resistance remain the same regardless of how many loads are added. - When one load “goes out” the others are unaffected.

Most circuits, however, are some combination of the two!

REAL WORLD EXAMPLES: ATTACHING SPEAKERS TO AN AMPLIFIER…..