Conduction Band – Electrons in the conduction band are able to move freely through the material in question, assuming the conduction band isn’t totally full.

Valence Band – The basic energy level of a material.

Band Gap – The gap between the Valence Band and the Conduction Band; depending upon the material, the gap’s size varies. In some cases, the band gap is insurmountable — you cannot get electrons from the Valence Band into the Conduction Band and you cannot get them to flow, at least not under normal operating circumstances. The larger the band gap, the more energy needed to move electronics from the Valence Bond to the Conduction Band.

Conductors – Have high electrical conductivity; this means that they facilitate the flow of electrons; they have a nearly full — but not completely full – conduction band. Electrons can move freely through these materials in response to an electric field applied to the material.

Current flow and electron flow move in opposite directions. In current flow, electrons move from positive to negative. In electron flow, electrons move from negative to positive.

Insulators –  Do not have electrons with the conduction band or they have a full conduction band (no room for electrons to move around; there are no free electrons). They impede the flow of electrons through the material. Most solids fall into this category (metals are an exception). Under normal circumstances, you can apply an electric field to insulators, but it won’t be enough to make electrons jump from the valence band to the conduction band, so the flow stops.

Semi-conductors – Have an almost empty conduction band, and an almost full valence band. The band gap is relatively narrow.  So, if you don’t apply a strong enough electric field, the material acts as an insulator. But, when you apply the right amount of energy and electric field, it will allow electrons to jump from the valence band to the conduction band, and move freely in the material.

Semi-conductors have impurities purposely inserted into them (this is called “doping”); these impurities allow people to control the energy levels required for the material to conduct electricity. This is the basis for solid-state electronics.

Voltage is a lot like water pressure — it is the amount of electrical pressure applied. The higher the voltage, the more electronics want to move from the concentration of electrons (the negative “side”) to the more positive “side.”

Current – the actual flow of electrons.

Voltage x Current = Power

Individual Components, and What They Do:

Resistors – A resister resists — but does not halt — the flow of electricity.

Sometimes you have to limit the amount of electricity that can flow through part of a circuit within a given amount of time. This is similar to the way a faucet can limit the amount of water that can flow into a sink.

Resistors reduce the amount of voltage placed on other electronic components within a circuit by restricting the amount of current that can flow through the resistor.

Resistors allow us to standardize batteries by controlling the voltage in electronic components. This allows us to ensure electronic components receive just the right amount of voltage.

There are many types of  resistors designed to work on specific amounts of electrical power. Some of them have changeable resistor values dependent upon the amount of voltage placed across them. These are called non-linear or voltage-dependent resistors.

Resistor values can also change when the temperature of the resistor changes. Some resistors can also be mechanically adjusted.

The unit of measurement for resistance is the Ohm. Resistor values are 10 percent apart from one another, and resistors are color-coded with bands (rings) of color; the first ring represents the first digit of the resistor’s value. So, you look at the color of the first ring, and cross-reference it with a color index that will tell you what the value of the resistor.

The second ring tells you the value of the second digit.

The third ring tells you the power of 10 to multiply by, such as ten thousand.

First ring -2

Second ring – 7

Multiply by ten thousand

This would give you 27,000 Ohms

The fourth ring tells you the tolerance of the resistor (plus or minus a certain percentage).

In general, the larger the resistor the more power it can handle.

Capacitors – Capacitors are similar to batteries in that they are a means of storing electrical energy. Unlike batteries, which create a flow of electrical energy through a chemical reaction that is steady, capacitors release the flow of electrical energy all at once.

Capacitors can pass alternating current freely. AC current passes through a capacitor as if it isn’t really there. Direct current, however, will charge a capacitor. It will build up electrons on one side of the capacitor (one lead) while the other side does not get a build up.  This creates a difference in voltage.

All capacitors contain the same fundamental parts: At least two conductive plates separated by a non-conductive material, called the dielectric.

The amount of charge a capacitor holds is measured in a unit called a Farad; a Farad is a large amount of capacitance, and we usually talk about micro-Farads, which are each one-millionth of a Farad.

Capacitance is dependent upon surface area — it is directly proportional to the surface area of the leads (the capacitance plates); and capacitance is indirectly proportional to the distance between the plates. This means that the greater the distance between the plates the lower the capacitance.

Capacitance is also dependent upon the dielectric constant of the insulating material.

Capacitors are used for things that need a quick release of electricity rather than a steady flow, such as a traditional flash on a camera. (Newer style cameras use a different approach.)

The voltage of a capacitor cannot change instantly. Quick voltage changes in a capacitor produce large current changes. Capacitors store energy in an electric field.

Inductors –

 

 

 

Source: Techstuff Podcast from How Stuff Works, episode published June 15, 2015