Electrical Info

This site is great for students or hobbyists looking to expand their understanding of general electrical topics.


resistor Resistors

Resistors are one of the most common components found in electric circuits. The unit of measure for resistance (R) is the ohm. Resistors come in various sizes, types, and ratings to accommodate the needs of almost any circuit application.

They are commonly used to limit the flow of current through the circuit.  By connecting resistors of the proper value, almost any voltage desired can be obtained.

Fixed resistors

have only one ohmic value, which cannot be changed or adjusted. There are several different types of fixed resistors.

Composition carbon resistor

–       Is one of the most common types

–       They are made from a compound of carbon graphite and a resin bonding material. The proportions of carbon and resin material determine the value of resistance

–       Carbon resistors are very popular for most applications because they are in- expensive and readily available. They are made in standard values that range from about 1 ohm to about 22 mega ohms

carbon resistor Resistors

Metal Film Resistors

–       Metal film resistors are constructed by applying a film of metal to a ceramic rod in a vacuumThe type of metal used to form the film and the thickness of the film determines the resistance.


–       They are superior to carbon resistors in several respects.

–       Metal film resistors do not change their value with age, and their toleranceis generally better than carbon resistors.

–       Tolerance indicates the plus and minus limits of a resistor’s ohmic value.

–      The disadvantage is that it costs more.

Carbon Film Resistors

Another type of fixed resistor that is constructed in a similar manner is the carbon film resistor. These are made by coating a ceramic rod with a film of carbon instead of metal. They are less expensive to manufacture than metal film resistors and can have a higher tolerance rating than composition carbon resistors.

carbon film resistor Resistors

Metal Glaze Resistors

The metal glaze resistor is also a fixed resistor, similar to the metal film resistor. They are made by combining metal with glass. The compound is then applied to a ceramic base as a thick film. The resistance is determined by the amount of metal used in the compound. Tolerance ratings of 2% and 1% are common.

Wire-Wound Resistors

Wirewound Resistors

Wire-wound resistors are are made by winding a piece of resistive wire around a ceramic coreThe resistance of a wire-wound resistor is determined by three factors:

–       The type of material used to make the resistive wire

–       The diameter of the wire

–       The length of the wire

They are generally used when a high power rating is needed. They can operate at higher temperatures than any other type of resistor.  The disadvantage  is that they are expensive and generally require a large amount of space for mounting. They can also exhibit an amount of inductance in circuits that operate at high frequencies. This added inductance can cause problems to the rest of the circuit.

Color Code

color code Resistors

The value of a resistor can often be determined by the color code. Many resistors have bands of color that are used to determine the resistance value, tolerance, and in some cases reliability. The color bands represent numbers. Each color represents a different numerical value.

Variable Resistors

A variable resistor is a resistor whose values can be changed or varied over a range. They can be obtained in different case styles and power ratings. These resistors can be adjusted from its minimum to maximum value by turning the control. Variable resistors are known by several common names. The most popular is the potentiometer. Another common type is the rheostat.

metal film resistor

Film Resistors

“Film Resistor” is a generic term consisting of Metal Film Resistor, Carbon Film and Metal Oxide Film resistor types. These types of resistors are normally made by depositing a pure metal, like nickel onto an insulated ceramic rod. An oxide film, like tin-oxide can sometimes be substituted for a pure metal.

Film resistors can be called “thick film” resistors by increasing the thickness of the deposited film. Also decreasing the amount of film will create a “thin film” resistor. Adding or decreasing the film will in turn control the resistive value of the resistor. A laser is then used to etch a high precision spiral groove into the film. The groove effects the film by creating a conductive or resistive path around the resistor some what like a coil.

This specific way of manufacturing allows for a more precise tolerance. It can be as low as 1% or lower. This method is much more effective than carbon composition types. Much higher ohmic values can be achieved by film type resistors compared to other resistors.

Metal Film Resistor

A typical kind of axial resistor today is described as a metal film resistor. Steel electrode leadless face (MELF) resistors commonly use the very same technology, but are a cylindrically shaped resistor designed for area positioning. Take note that additional types of resistors (e.g., carbon composition) are also offered in MELF bundles.

Steel film resistors are generally covered with nickel chromium (NiCr), however could be covered with any of the cermet materials detailed above for thin metal resistors. Unlike slim film resistors, the component might be applied making use of various methods compared to sputtering (though that is one such technique). Even, unlike thin-film resistors, the resistance worth is figured out by cutting a helix through the layer as opposed to by etching. (This resembles the method carbon resistors are made.) The outcome is an affordable resistance (0.5 %, 1 %, or 2 %) as well as a temp coefficient that is usually between FIFTY as well as A HUNDRED ppm/K. A Metal film resistor has really good noise features and inexpensive non-linearity due to a reasonable current coefficient. Helpful are the parts reliable resistance, temperature coefficient and durability.

metal film metal film resistor


 Metal Oxide Film

Metal-oxide film resistors are constructed from steel oxides such as tin oxide. This outcomes in a higher operating temp and also greater stability/reliability than Steel film. They are made use of in applications with high endurance demands.


One of the most important theories in the study of electricity is Magnetism.  Most Electrical power in the world is created by magnetism.  The Greeks discovered it over 2000 years ago when a certain rock was attracted to iron.

Permanent Magnets

Permanent magnets are magnets that require no power or force to maintain their field.  A basic law of magnetism states that energy is required to create a magnetic field, but no energy is required to maintain a magnetic field.

Electron Theory of Magnetism

electron theory flow Magnetism

Electrons spin on their axes as they orbit around the nucleus of the atom.  This spinning motion causes each electron to become a tiny permanent magnet.  Not all electrons spin in the same direction however.   Electrons that spin in opposite directions tend to form pairs. These pairs cancel each other out as far as having a magnetic effect on other objects.  Only 3 materials actually form natural magnets: iron, cobalt, and nickel.

Atoms in a magnetized material are all aligned in a perfect orderly fashion.  When a magnet is cut apart, each piece becomes its own magnet.

broken magnet Magnetism

Magnetic Materials

There are three basic classes of magnetic materials:

–       Ferromagnetic materials are metals that are easily magnetized.  Ex: iron and nickel

–       Paramagnetic materials are metals that can be magnetized but not as easy as ferromagnetic materials.  Ex: platinum and titanium

–       Diamagnetic materials are either metal or nonmetal materials that cannot be magnetized. Magnetic lines tend to go around them instead of through them. Ex: brass and copper.

Magnetic Lines of Force

lines of flux Magnetism

Magnetic lines of force are called flux.  Magnetic lines of flux repel each other and never cross.  A basic law of magnetism states the unlike poles attract and like poles repel. 

magnetic attraction 300x125 Magnetism


A basic law of physics states that whenever an electric current flows through a conductor, a magnetic field is formed around the conductor.  Electromagnets need current flow to produce a magnetic field.  Current flowing through a conductor produces a magnetic field around the conductor.  If the conductor is wound into a coil, the magnetic lines of flux add to produce a stronger magnetic field.  An increase in current flow causes an increase in magnetic field strength.  The number of flux lines produced by an electromagnet can be determined by:  The number of turns of wire, and the amount of current flow through the wire.

flux Magnetism

conductor current Magnetism

The strength of an electromagnet is equal to its ampere-turns. (Current x turns of wire.)  The core material is also used to determine the strength of the magnet.  The permeability of the core material is its ability to become magnetized.  Materials permeability number multiples the strength of the magnet.  Reluctance is a materials resistance to magnetism.  If the current flow in an electromagnet is continually increased, the magnet eventually reaches a point where its strength increases only slightly.  This is called the point of saturation.  When current flowing through an electromagnet is stopped, the remaining magnetism is called the residual magnetism.

Series Circuits

series circuit Series Circuits

series circuit is a circuit that has only one path for current to flowBecause there is only one path for current flow, the current (A) is the same at any point in the circuit.

Ohm’s Law

The Ohm’s law formulas are used when finding unknown values in the circuit

ohms law1 Series Circuits
V – Volts                   I – Current              R – Resistance

Voltage Drops in a Series Circuit

Voltage is the force that pushes the electrons through a resistance. The amount of voltage required is determined by the amount of current flow and resistance.  The amount of voltage necessary to push the current through each resistor is known as voltage drop. 

series circuit volatge drop Series Circuits

Voltage drop and be determined by placing a voltmeter across a resistor.   In a series circuit, the sum of all the voltage drops across all the resistors must equal the voltage applied to the circuit.

Resistance in a Series Circuit

Because only one path exists for the current to flow through a series circuit, it must flow through each resistor in the circuitEach resistor limits or impedes the flow of current in the circuit. Therefore, the total amount of resistance to current flow in a series circuit is equal to the sum of the resistances in that circuit.

Rtotal = R1 + R2 + R3

Calculating Series Circuit Values

series circuit resistors Series Circuits

Three rules can be used with Ohm’s law for finding values of voltage, current, resistance, and power in any series circuit:

1. The current is the same at any point in the circuit.

2. The total resistance is the sum of the individual resistors.

3. The applied voltage is equal to the sum of the voltage drops across all the resistors.

The amount of current flow in the circuit can be found by using Ohm’s law:


If current is known then you can determine how many volts are required to push a certain amount of amps through the resistor

Solving Circuits

The first step in finding the missing values in the circuit is to find the total resistance (RT). This can be done using the second rule of series circuits, which states that resistances add to equal the total resistance of the circuit.

Rtotal = R1 + R2 + R3

The total resistance is then used to find the Current of the circuit.

ohms law trianlge1 Series Circuits

power formula Series Circuits

Divide the total voltage of the circuit by the total resistance. Since the current is the same at any point in a series circuit, the voltage drop can also be determined for each resistor.


Each resistors dissipates a certain amount of heat.(power) The power can be found using these formulas depending on the values known:

A good rule to remember when calculating values of electric circuits is that the total power used in a circuit is equal to the sum of the power used by all parts.

Ptotal = P1 + P2 + P3

Parallel Circuits

Parallel circuits

Parallel Circuits

Parallel circuits are probably the type of circuit with which most people are familiar. Most devices such as lights and receptacles in homes and office buildings are connected in parallel. Imagine if the lights in your home were wired in series. All the lights in the home would have to be turned on in order for any light to operate, and, if one were to burn out, all the lights would go out. The same is true for receptacles. If receptacles were connected in series, some device would have to be connected into each receptacle before power could be supplied to any other device.

Parallel Circuit Values


 Parallel Circuits

Parallel circuitsare circuits that have more than one path for current flow.  One of the rules for parallel circuits states that the total current flow in the circuit is equal to the sum of the currents through all the branchesThis rule is known as current adds. The amount of current leaving the source mustreturn to the source.

Voltage Drop

A second rule for parallel circuits states that the voltage drop across any branch of a parallel circuit is the same as the applied voltage. For this reason, most electric circuits in homes are connected in parallel. Each lamp and receptacle is supplied with 120 volts.

Total Resistance

Parallel Circuits

The total resistance of a parallel circuit is always less than the resistance of the lowest value resistor, or branch, in the circuitEach time another element is connected in parallel, there is less opposition to the flow of current through the entire circuit.  Imagine a water system consisting of a holding tank, a pump, and return lines to the tankAlthough large return pipes have less resistance to the flow of water than small pipes, the small pipes do provide a return path to the holding tank. Each time another re- turn path is added, regardless of size, there is less overall resistance to flow and the rate of flow increases.

Finding the resistance of a parallel circuit is the reciprocal formula of a series circuit

Multiple Tapped Transformer Primary Winding