## The nuts and bolts of Electricity

Enter the Electronics

Enter the Electronics

~~Electronics is the discipline dealing with the development and application of devices and systems involving the flow of electrons in… ~~crap…

Being an electrical engineer you can’t resist sounding like one sometimes… Anyways, this lecture is dedicated to simply some of the key building blocks and core fundamentals of practical electronics.

In Electronics, obviously we deal with electrons (Electricity to be more practical) and in order to utilize electricity, we need to shape it, mold it, size it, resize it, etc to meaningfully and purposefully utilize it. To do all of that, we invented some small and beautiful basic things called electronic components which are like building blocks. Using these components we actually alter the electricity in a planned manner to make use of it.

Before getting to these components, its important to take a small detour and touch upon 2 types of Electricity namely, AC & DC, or should we say ACDC… yeaaah!

As this is supposed to be a small detour, I will be as quick as possible to drive home the concept.

We know that Electricity deals with flow of electrons and this flow is nothing but current. This current can obviously flow in only two directions in a wire, say left to right or right to left. If the current is in one direction (Anyone) then its called Direct Current (DC). The other case that is possible is that when the current repeatedly goes back and forth between the two directions, in other words when it alternates and that case is called as Alternating Current.

Typically when electricity is generated from a generator, which works on Faraday’s law of Induction, AC is generated. This is intuitively understandable given the fact that the generator is normally rotated by a stream of steam or water and as it rotates a rotating or alternating current should get generated. On the other hand, any common battery cell generates Direct Current and in fact is known as DC Battery.

At This point we should also know that, Across the globe the power generation and supply at homes are AC Power.

— End of Detour —

There are only 3 basic blocks of Electronics: Resistors, Capacitors or Condensers and Inductors.

It is often said that if you look little closer to pay attention to just the names of things you understand a lot about them by doing just that.

At this stage we are pretty clear that electric current is nothing but a flow of electrons, if we think about it as a flow of water in a pipe then it makes things much clearer for comprehension. Consider the flow of water in the pipe, its very easy to visualize that its much easier for water to flow in a thicker pipe than a thinner pipe at a fixed pressure. What it suggests is that the thickness of the pipe actually constraints the flow of water, pretty intuitive. Actually a very similar scenario happens with current flowing in a conductor, the thicker the cross section area, the easier it is for electrons to flow. Beside that, we know that there are relatively more free (loosely held) electrons in certain materials than the other and those are in the category of conductors. In very good conductors those free electrons are in abundance like in copper, silver, etc. and hence they relatively do not resist the flow of electrons as much as other materials like the ones we call as non conductors or insulators, like plastic and wood.

Now taking our same water in pipe analogical example to other dimension, its is very easy to visualize that it is easier for water to flowing a shorter pipe than in a longer pipe, naturally this is so, because, you can easily sense that longer pipe will restrict the flow for long and hence it will mean more push or thrust required to push water.

Similarly, a shorter conductor of same size will restrict the flow of electrons lesser than the longer one.

These 2 dimensions which we tried to explore, one being Size and other being Length actually give rise to what is known as resistance, as the name suggests itself.

Resistance hence is the property of substance which restrict the flow of current/electrons.

We can now combine the two resistance cases discussed above together as follows:

- If area/size increases Resistance decreases, implying resistance in inversely proportional to size.
- If Length of the conductor increases then Resistance Increases, implying Resistance is directly proportional to length.
- Also, Resistance will definitely vary from one substance to another basis that substance’s own inherent properties and that will be constant for each substance.

These three are no less than

3 Golden rule of Resistanceand have far reaching impacts than it appears at this stage.

We now have a formula for Resistance:

**R= ρ ^{Length }⁄_{Area}**

The ρ, is called resistivity and is fixed for a substance.

The SI unit of electrical resistance is the ohm (Ω).

It is the ability or “capacity” to store energy in the form of an electrical charge producing a potential difference (Static Voltage) across its plates, much like a small rechargeable battery. The common term voltage is nothing but a higher energy potential, an energy which is in the form of charge. Two substances both charged differently, have a difference in charge and hence difference in energy, this means if you connect both of them by a conductor then the higher charge will flow to the lower one until they come at same level and this flow of charge will create a current just like connecting two tanks at different height by a pipe, the water will flow until the levels are same.

Capacitors are similar devices as they hold and store charge on two plates within them until a conductor carrying a lower or higher charge doesn’t come in contact. Again, it seems intuitive that lager the capacitor size larger should be the ability to store charge and closer the two plates more will be the strength of attraction (Electric Field) and hence just like the way we discussed and arrived at Resistance formula we can get to the capacitance.

**C = ε ^{Area }⁄_{Distance}**

Here, ε is called the Dielectric Constant. Don’t get bothered by the weird name, it is just a constant for different types of materials that can be between the plates of a capacitor, it can be air, paper, plastic and hence the constant will be different for each one. *(For the more curious heads, it is a measure of a material’s ability to store an electric field in the polarization of the medium relative to vacuum.)*

The capacitance is a function only of the geometry of the design (e.g. area of the plates and the distance between them) and the permittivity of the dielectric material between the plates of the capacitor. For many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them.

The SI unit of capacitance is the farad (symbol: F), named after the English physicist Michael Faraday. It is often measured in (Micro) μF, (Nano) nF, (Pico) pF as practically Farad is a very large unit from construction point of view.

We will be exploring the numerous and really numerous kind of capacitors subsequently as we get deeper into the fun forest.

Just the way a Capacitor stores energy by means of charge and hence in the form of electric field, an inductor staores energy in the form of changing current and hence in the form of magnetic field.

If a changing current is fed to a coil of a conductor there would be an electricity induced (Refer previous Lecture) in it. The property of the coil of inducing electricity due to the changing current linked with it is known as inductance of the coil.

An inductor is characterized by its inductance, which is the ratio of the voltage to the rate of change of current. In the International System of Units (SI), the unit of inductance is the henry (H) named for 19th century American scientist Joseph Henry. In the measurement of magnetic circuits, it is equivalent to weber/ampere. Inductors have values that typically range from 1 µH (10−6 H) to 20 H. Many inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic field and thus the inductance.

One very fundamental fact is that all these three components and properties only react to electromagnetism and they neither behave in a generative manner nor do they consume or degenerate electromagnetism. This is the reason they are also known as

PASSIVE COMPONENTS.

We have learned that resistance is the property of a material to resist the flow of current and a resistor does that irrespective of the nature of current, whether the current is fluctuating in nature or constant, in simpler words, whether it is AC or DC.

In case of a Capacitor, we know that it is made out of 2 plates facing each other and physically separated, this arrangement enables this to store charge on the 2 plates and store electrostantic energy between these plates. However it is not iff=icult to visualize that when a DC current is applied, the capacitor plates gets charged and once charged there is no current flow bevcause of the physically separated plates and they behave as open circuit. Imagine a case when an Alternating Current is applied, this cause the capacitor to get charged and discharged as the curremty alaternates from positive to negative and hence it will appear that the current actually flows.

This is a very unique behavior and must be remembered that, capacitors always pass AC and not Block DC.

The resistance offered by capacitor varies inversely with frequency.

**X _{C} (Resistance offered by Capacitor, called reactance) = 1/ωC**, ω is the angular frequency equal to 2π times frequency (as in one cycle of a wave the 2π angle that is one full rotation happens).

As ω decreases and become zero (in case of DC), the Zc, becomes infinite and capacitor blocks DC, as ω increases, the resistance decreases and lesser resistance is offered by capacitor.

Lets get to the other guy, An Inductor we know is a coil, obviously if we pass a constant current or DC, then it will create a constant magnetic field and will not lead to any induction and there is no change in the field , also the coil being made from the inductor will freely pass the Direct Current. In case of AC current the, induction will happen as Faraday taught us and the induced voltage within the coil will generate the current in opposite direction as Lenz taught us and hence these induct current will oppose the AC current which we had supplied, in other words, an Inductor blocks the AC current.

The resistance offered by inductor varies directly with frequency.

**X _{L} (Resistance offered by Inductor, called reactance) = ωL**, ω is the angular frequency equal to 2π times frequency (as in one cycle of a wave the 2π angle that is one full rotation happens).

As ω decrees and become zero (in case of DC), the XL, becomes zero and passes DC, as ω increases, the resistance decreases and lesser resistance is offered by Inductor.

We learned some very remarkable concepts and here is the summary of all.

Component |
DC |
AC |
High Frequency |
Low Frequency |

Resistor | Pass | Pass | Neutrally pass | Neutrally pass |

Capacitor | Block | Pass | Pass with Lower Resistance | Blocks with higher resistance |

Inductor | Pass | Block | Blocks with higher resistance | Pass with Lower Resistance |

Simply put, let us remember following statements in a more interpret-able manner:

**Resistance resits all type of currents****Capacitor resists DC****Inductor resists AC**

In a circuit, a combination of these components become s complex resistance, called as

IMPEDANCE.