The term is usually taken to mean a continuous path composed of conductors and conducting devices and including a source of electromotive force that drives the current around the circuit. A circuit of this type is termed a closed circuit, and a circuit in which the current path is not continuous is called an open circuit. A short circuit is a closed circuit in which a direct connection is made, with no appreciable resistance, inductance, or capacitance, between the terminals of the source of electromotive force. Current flows in an electric circuit in accordance with several definite laws . The basic law of current flow is Ohm's law, named for its discoverer, the German physicist Georg Ohm. Ohm's law states that the amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive force impressed on the circuit and inversely proportional to the total resistance of the circuit. The law is usually expressed by the formula I = V/R, where I is the current in amperes, V is the electromotive force in volts, and R is the resistance in ohms (see Electrical Units). Ohm's law applies to all electric circuits for both direct current (DC) and alternating current (AC), but additional principles must be invoked for the analysis of complex circuits and for AC circuits also involving inductances and capacitance.

SERIES

BASIC RULES A series circuit has certain characteristics and basic rules summized here:

1. The same current flows through each part of a series circuit.

2. The total resistance of a series circuit is equal to the sum of individual resistances.

3. Voltage applied to a series circuit is equal to the sum of the individual voltage drops.

"1. The same current flows through each part of a series circuit."

In a series circuit, the amperage at any point in the circuit is the same. This will help in calculating circuit values using Ohm's Law.You will notice from the diagram that 1 amp continually flows through the circuit. We will get to the calculations in a moment.

"2. The total resistance of a series circuit is equal to the sum of individual resistances."

In a series circuit you will need to calculate the total resistance of the circuit in order to figure out the amperage. This is done by adding up the individual values of each component in series.

In this example we have three resistors. To calculate the total resistance we use the formula:

RT = R1 + R2 + R3

5 + 5 + 10 = 20 Ohms

R total is 20 Ohms

Now with these two rules we can learn how to calculate the amperage of a circuit.

Remember that Ohm's law is I=V/R Total.

RT = 20 Ohms

I = V / RT

I = 20V / 20 Ohms

I = 1 Amp

If we had the amperage already and wanted to know the voltage, we can still use Ohm's lawl

V = I x R total

V = 1 A x 20 Ohms

V = 20 V

"Voltage Drops"

A voltage drop is the amount the voltage lowers when crossing a component from the negative side to the positive side in a series circuit.

According to the previous rules we figure out the total resistance then we calculate the amperage in the circuit.

Now that we know the amperage for the circuit (remember the amperage does not change in a series circuit) we can calculate what the voltage drops across each resistor are using Ohm's Law (V = I x R).

V1 = 1A x 5 Ohms = 5 V

V2 = 1A x 5 Ohms = 5 V

"3. Voltage applied to a series circuit is equal to the sum of the individual voltage drops."

This simply means that the voltage drops have to add up to the voltage coming from the battery or batteries.

V total = V1 + V2 + V3 ...

This means that 5V + 5V = 10V.

PARALLEL

A Parallel circuit is one with several different paths for the electricity to travel. It's a river that has been divided up into smaller streams. However, all the streams come back to the same point to form the river once again.

The parallel circuit has extremely different characteristics than a series circuit. For one, the total resistance of a Parallel Circuit is NOT equal to the sum of the resistors.

BASIC RULES A Parallel circuit has certain characteristics and basic rules summized here:

1. A parallel circuit has two or more paths for current to flow through.

2. Voltage is the same across each component of the parallel circuit.

3. The sum of the currents through each path is equal to the total current that flows from the source.

4. You can find total resistance in a Parallel circuit with the following formula:

1/Rt = 1/R1 + 1/R2 + 1/R3 +...

Rt = R (t)otal

"1. A parallel circuit has two or more paths for current to flow through."

The flow of electricity is divided between each according to the resistance along each route.

"2. Voltage is the same across each component of the parallel circuit."

The voltage will be the same anywhere in the circuit.

"3. The sum of the currents through each path is equal to the total current that flows from the source."

Simply remember for now that the branch currents must tally to equal the source current.

"4. You can find TOTAL RESISTANCE in a Parallel circuit with the following formula:

1/Rt = 1/R1 + 1/R2 + 1/R3 + ...

We will use a parallel circuit with 3 paths as an example.

The power source is providing 10 volts and the value of the resistors are 4 Ohm, 4 Ohm and 2 Ohm.

Voltage = 10V

R1 = 4 Ohm

R2 = 4 Ohm

R3 = 2 Ohm

1/RT=1/R1 + 1/R2 + 1/R3

Therefore: 1/RT=1/4 + 1/4 + 1/2

Rt = 1/1

Rt = 1 Ohm