CIRCUITS

Circuits A Circuit is a set of electrical components connected so that they provide one or more complete paths for the movement of charges.

Schematic Diagrams and Circuits Schematic diagram: a diagram that depicts the construction of an electrical apparatus Light bulb filaments are resistors; so symbols for bulbs may be the same as resistors

Series Circuits A series circuit is a circuit in which resistors are arranged in a chain, so the current has only one path to take. The current is the same through each resistor. If one bulb goes out, they all go out.

Parallel Circuit A parallel circuit is one that has two or more paths for the electricity to flow – similar to a fork in a river In other words, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out there is still current flowing to the others.

Series Circuit Equations The following rules apply to a series circuit: The sum of the potential drops equals the potential rise of the source.

The current is the same everywhere in the series circuit. The total resistance of the circuit (also called equivalent resistance) is equal to the sum of the individual resistances.

In this animation you should notice the following things: The battery or source is represented by an escalator which raises charges to a higher level of energy. As the charges move through the resistors (represented by the paddle wheels) they do work on the resistor and as a result, they lose electrical energy. The charges do more work (give up more electrical energy) as they pass through the larger resistor. By the time each charge makes it back to the battery, it has lost all the energy given to it by the battery. The total of the potential drops ( - potential difference) across the resistors is the same as the potential rise ( + potential difference) across the battery. This demonstrates that a charge can only do as much work as was done on it by the battery. The charges are positive so this is a representation of Conventional Current (the apparent flow of positive charges) The charges are only flowing in one direction so this would be considered direct current ( D.C. ).

Parallel Circuit Equations The following rules apply to a parallel circuit: The potential drops of each branch equals the potential rise of the source. The total current is equal to the sum of the currents in the branches. The inverse of the total resistance of the circuit (also called equivalent resistance) is equal to the sum of the inverses of the individual resistances.

One important thing to notice from this last equation is that the more branches you add to a parallel circuit (the more things you plug in) the lower the total resistance becomes. Remember that as the total resistance decreases, the total current increases. So, the more things you plug in, the more current has to flow through the wiring in the wall. That's why plugging too many things in to one electrical outlet can create a real fire hazard.

In this animation you should notice the following things: More current flows through the smaller resistance. (More charges take the easiest path.) The battery or source is represented by an escalator which raises charges to a higher level of energy. As the charges move through the resistors (represented by the paddle wheels) they do work on the resistor and as a result, they lose electrical energy. By the time each charge makes it back to the battery, it has lost all the electrical energy given to it by the battery. The total of the potential drops ( - potential difference) of each "branch" or path is the same as the potential rise ( + potential difference) across the battery. This demonstrates that a charge can only do as much work as was done on it by the battery. The charges are positive so this is a representation of conventional current (the apparent flow of positive charges) The charges are only flowing in one direction so this would be considered direct current ( D.C. ).

Kirchoff’s Laws Loop Rule: Junction Rule: ∑V = 0 in any continuous loop ± V and ± IR depending on power supplies orientation & chosen I direction Junction Rule: ∑I into junction = ∑I leaving junction Use Junction Rule substitution to eliminate variables & solve using simultaneous equations