A circuit is the path a charged particle travels. Electrical circuits control this path in order to predict the outcome. Below is an example electrical circuit.
An electric field is set up between the plus and minus sides of the battery. The electric field is directed by the wires. The electric field provides the force to move charges through the wire. By definition, the charges flow from high energy to low energy. This means they flow from the positive side to the negative side. To move from the positive side of the battery, the charge's sign must be positive because positives repel each other. Because of this, the current is defined as the flow of positive charges. (Engineers look at current differently because electrons flow through wires and not positive ions. Engineers define current as the flow from negative to positive. This means they look at the flow of negative charges, Mathematically nothing changes until there is a need to describe the direction of the current. Physicists to not use this description of current.)
Charges carry the energy used by the electrical components, such as resistors. In the animation above the energy electrical potential energy is modeled by the rate the charge flashes. The current is described by how many charge flow past a point in a second. This means faster charges are the higher current.
The charges themselves are not used up by the resistors. (This can be seen in the animation below by the fact that charges leave the light bulb after it has been lit up.)
Instead some of charge's energy is used by the resistor. The same amount of energy is used up from each charge. Not all of the charge's energy is used up, only a small amount is siphoned off the charge. If the circuit is using a 9 Volt battery them 9 electronVolts of energy is used up for every elementary charge that passes through the resistor. The energy supplied by the circuit is measured in units called Volts. A volt is a Joule per Coulomb's worth of charge.
Schematics
To represent the different components of circuit a collection of symbols are used. These symbols create something called "schematic diagram." This diagram represents the real components.
The lines connecting the pieces of the circuit represent the wires.
Where three or more wires come together is called a junction.
Junctions either split or combine the current. This means that junctions change the amount of current in connecting wires. To understand this, visualize water flowing through pipes as it enters and leaves at a junction. The pipes represent the wires in a circuit and the water represents the charges flowing along the wires. Look how the flow rates change in the animation.
The power source for direct current (d.c.) power sources is usually referred to as a battery. There a few variations of a batteries symbol. But they all have alternating long and short straight lines. Because the battery is polarized, (has a plus and minus side,) the positive side is illustrated by the longer line. These batteries have the positive side labeled but on a schematic diagram they are usually not labeled.
A second way to draw battery is with 2 symbols. The circle represents the positive side of the battery. The negative side is represented with a set of triangular lines. This symbol is called the ground symbol.
Resistors are represented by a line with squiggles. Generally resistors will be represented by 3 mountains and 3 valleys. Light bulbs will also be represented as resistors. [In reality, light bulbs are more complicated than resistors because their resistance changes with time and temperature. But for an introductory text, this behavior will be ignored.]
An electrical circuit is a path for charges to travel from the positive to negative side of the battery.
by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)
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