Calculations

Increasing Resistance

The purpose of this section is to not simply discuss what a circuit is, or how resistors function, but more how do multiple resistors function within a circuit. It is important to discuss how these components function together because some projects may require the next step in electrical design to function properly.

The MAJORITY of projects can function properly and will not require multiple components within the circuit IF you use a variable voltage power supply.

Adding resistors and rheostats to a circuit become necessary when a design calls for a solid-state fixed voltage power supply or when using a large cell battery as the circuit’s power source.

When components are placed in series the total circuit resistance (Rt) is simply the sum of each component’s individual resistance.

There is no real need to make any special calculations when figuring the amperage of components placed in series.

The two main ways that components are placed within a circuit are called Series or Parallel.

The ways these components function together in regards to voltage, resistance and current vastly differ between a series and parallel circuit. Knowing how these function will allow one to pick the most ideal configuration for optimal function.

Components are attached end-on-end in a straight line

Components have one common point of origin and termination.

You may wish to print this PDF and follow along as you read through this next section.

The total resistance of any two or more resistors / components placed in series will always be GREATER than the value of the largest resistor in the circuit

When components are placed in parallel the total circuit resistance (Rt) is quite a bit different than a series circuit.

In a parallel circuit, the total resistance (or equivalent resistance) is always less than the SMALLEST resistor in the parallel circuit. The total resistance will always decrease as additional parallel resistors are added

The total resistance of a circuit in parallel is determined by taking the reciprocal value of each individual resistor, and that inverse of the algebraic sum

Parallel resistance give a value known as Conductance, which is the reciprocal (or the inverse) of resistance.

Think of adding resistors in series is the same as adding more length to your NiChrome Wire.

Think of adding resistors in parallel is the same as adding more diameter to your NiChrome Wire.

Two components in parallel are a bit easier to calculate, by using this equation.

When components are placed in series the total circuit voltage is equal to the voltage supplied by the power supply (Vp). However, the amount of voltage applied to each individual component is different.

Ohm's Law
Resistance (Ohms) = Volts / Current (Amperes)

Joule's Law
Power (Watts) = Volts * Current (Amperes)

Let us not forget the electrical laws at play...

COMMON CURRENT

COMMON VOLTAGE

When components are placed in series the total circuit current (I) is the same going through each component within the circuit.

The current flowing through one component must also flow through the others as it can only take one path from the positive to negative power supply terminals. Therefore the amount of current that flows through each component is the same as every other point within the circuit.

The total circuit current flow is a function of the voltage from the power supply (Vp) and the total circuit resistance (Rt).

When components are placed in parallel the total circuit current (I) is the sum of each individual component’s current.

The amount of current flowing through each component in a circuit is not necessarily the same value. The current flow is a function of that component’s own resistance and the applied power supply voltage (Vp).

The amount of voltage applied to each individual component is referred to as the “Voltage Drop”.

The voltage drop across each component is a function of it’s own resistance and the Common Current. The sum of the voltages across each component is equal to the voltage across the entire circuit.

When components are placed in parallel the total circuit voltage is applied equally across all components within that circuit.

While the voltage applied to a circuit remains constant from the power supply (Vp), and it is the current that changes as a function of resistance, you may calculate the total circuit voltage (Vp) by using the total current (I) and total resistance (Rt).