### Mutual Inductance and Inductive Reactance

I promised no more math in the last session, and it was difficult. We could have covered the number of turns to inductance:
but we didn't. We could have covered the math behind inductors in parallel:
but we didn't. But we will cover just a little math in this lesson.

When AC is applied to a coil, a varying magnetic field will be produced around it. When another coil is placed within that magnetic field, it will induce a current flowing in that coil. This principle is called MUTUAL INDUCTANCE The amount of mutual inductance between the two coils depends on the distance between the two coils, and the angle between the two coils. When two coils are linked together via mutual inductance in this manner, we say that the coils are inductively COUPLED. When the mutually inductive coils are close to each other, we say that they are closely, or tightly coupled. When they are far apart, we say that they are loosely coupled. The greatest amount of coupling occurs when the coils are wound one directly over the other and on a closed iron core. The quantity of coupling between two coils is sometimes referred to as the Coefficient of Coupling. The formula for Coefficient of Coupling is:

Whew! Now that we've got the math out of the way, let's move on to the magic of electronics. We have already discussed that inductance is an opposition to the flow of current in an AC circuit by a coil. This is caused by the expanding and collapsing of the magnetic field. More important though, as the field expands and collapses, it generates a counter- electromotive force, by way of mutual inductance within the same coil. We call this SELF INDUCTANCE. Simply put, self inductance is when a coils magnetic field, produces an electric current within the same coil. This self inductance causes a resistance to AC current. But this resistance is not measured in Ohms, as normal resistance is. This resistance isn't even called resistance, it's called REACTANCE, because of the way it reacts with AC. In the case of a coil, it is specifically called INDUCTIVE REACTANCE, and its symbol is XL.

XL is a very special number in electronics. Let me say this another way:

XL is a very special number!

get the idea?

Now that I have your attention. XL is the variable number that we use while expressing the AC resistance of a coil. You will see this number in your sleep. You will eat with this number, you will go out on dates with this number and you will

MEMORIZE THIS FORMULA:
XL = 2Ï€fL

Where:
• f = the FREQUENCY in Hz
• L= the inductance of the coil in henries
• and
• Ï€= 3.1415926536..... (or 3.14 for short)
• It has been quite prominently established that I hate math as much as you do. However, as you have also found, in order to have a CLEAR understanding of how electronic circuits and components work - a fairly decent grasp of the basic math functions is required. I absolutely promise you that the math is almost done. We've covered MOST of the math important to basic electronic components, and we will cover more - but I won't push it. That isn't to say that if you are using this as a supliment to classroom study - that your teacher won't give you a MAJOR math test right after you read this! That being said - I wouldn't want you to fail the test - so another review of the more important formulae may be in order:
In Review, the formula for finding Resistance, Voltage, and Current within a circuit (Ohm's Law) is:

or or

Much Akin to it is "Ohm's Watts Law" for finding POWER
P=IE

The Formula for finding the TOTAL RESISTANCE (or inductance in the case of a coil) in series is
R1+R2+R3... = RTotal

The Formula for finding the TOTAL CURRENT in series is

which we haven't covered because it is not a very important formula. Not so important because of the following formula which is also true:

I1=I2=I3... = ITotal

CURRENT NEVER CHANGES in a series circuit!!! In short - if you can measure the current ANYWHERE within the series circuit - you know the current in the whole circuit! (Very handy when checking Christmas lights)

The Formula for finding the TOTAL RESISTANCE in a parallel circuit is

The Formula for finding the TOTAL CURRENT in parallel is
I1+I2+I3... = ITotal

The formula for Time and Frequency is
F=1/T (or T=1/F)

The formula for Peak vs Effective voltage is:
EPeak=1.41xEEff or EEff=.707xEPeak
What is the formula for Inductive Reactance?

XL = 2Ï€fL

RED? REALLY? Ok, perhaps I have stressed this point a bit too far, but then again, in electronics, and especially in radio electronics, you will see this formula again and again. Inductive reactance constitutes the resistance seen by an AC circuit when it runs into a coil. Sometimes, an inductor is called a CHOKE, because it chokes an alternating current flow. In power supplies, you may find a FILTER CHOKE, which opposes any ac frequencies, while allowing DC to pass through unharmed. Its purpose is to clean up the power supply voltages, so that no noise is seen on the power - just a clean DC source. There are both audio frequency chokes (AFC) and radio frequency chokes (RFC).

Another point, which I passed over previousely, is that there are several types of "RESISTANCE" found in AC electronics, some of which will be negligable, others you will find fascinating and extremely important to the study of electronics. I will try to cover in detail the important ones. I will also, (when I remember to) mention the lesser important ones, as I will at this time.

RELUCTANCE is a form of resistance which we have not discussed yet. The reason for not discussing it, is that in most electronic applications, you can pretend that it doesn't exist. Reluctance is actually the resistance, not to the flow of current, but to any MAGNETIC FIELD which cuts through any pre-existing magnetic field. To some small extent, this happens in all coils operating at AC, due to Self Inductance, or by way of Mutual Inductance. Mathematically speaking (oh no!) we say that it is equal to the MAGNETOMOTIVE FORCE / MAGNETIC FLUX, or that it is the reciprocal of PERMEANCE. Now, don't you feel safer? Isn't your life better, since you have learned that bit of trivia?

### Build a Low Noise And Drift Composite Amp Circuit Diagram

How to Build a Low Noise And Drift Composite Amp Circuit Diagram. This circuit offers the best of both worlds. It can be combined with a low input offset voltage and drift without degrading the overall system`s dynamic performance.
Low Noise And Drift Composite Amp Circuit Diagram

Compared to a standalone FET input operational amplifier, the composite amplifier circuit exhibits a 20-fold improvement in voltage offset and drift. In this circuit arrangement, A1 is a highspeed FET input op amp with a closed-loop gain of 100 (the source impedance was arbitrarily chosen to be 100 kfl). A2 is a Super Beta bipolar input op amp. It has good dc characteristics, biFET-level input bias current, and low noise. A2 monitors the voltage at the input of A1 and injects current to Al`s null pins. This forces A1 to have the input properties of a bipolar amplifier while maintaining its bandwidth and low-input-bias-current noise.

### High Power Output Amplifier TDA7294

The famous SGS-THOMSON ST Microelectronics has introduced a Hi-Fi DMOS high-power amplifier circuit TDA7294, its sound great taste bile, which due to its internal circuit from input to output are field-effect devices, rounded sound Mild, delicate Rounuan.  However, with its assembly amplifier, only TDA7294 single-output power is only 70 W, BTL access law is 100 W from top to bottom, do not feel that power cushion. The author several tests, used to promote TDA7294-level, direct-drive one to four pairs of high-power transistor parallel, the output of strong currents, the power output of 400 W (mono), and the circuit is simple and no need to debug that can reliably work Basically, the IC has maintained a sound and performance.  Ruzuo The figure below shows, R6 for the feedback resistor, the author of the value in debugging 22 k Î© more appropriate, R6 also decided this circuit gain, the gain value will increase.  Quiescent current depends on the power of R7, R8, when its value…

### Full Power Mobile Phone Jammer Circuit Diagram

Full Power Mobile Phone Jammer Circuit Diagram.To day if we are talking about expert Cell phone Jammers we are conversing about this schematic underneath. First off all you should be very very cautious how to use this apparatus. Its completely illegal and so the reason. I post this Circuit is only for educational and testing causes. This type of apparatus is being utilised by security for VIPS, particularly at their limousines to avoid blasting device initiating while the vehicle passes from the goal cell phone-bomb. Off course there are those who use it to make a antic or to make the persons crazy in the rectangle block you are.
The power of the jammer is currently sufficient to do your thing, but certainly you can place a 30W linear power amp at the RF output and impede a much wider locality. So, Be pleasant individual with that and recall that there are people who may need desperately to obtain or make a call and one of them could be you! And if you can't oppose of functioning …