Questions tagged [theory]

Theory is a contemplative and rational type of abstract or generalizing thinking, or the results of such thinking. Depending on the context

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72
votes
6answers
41k views

Ceramic caps vs electrolytic. What are the tangible differences in use?

A quick google around and all I seem to be able to find are people talking about the physics & the chemistry of the capacitors but not how this affects choosing which to use. Avoiding talking ...
41
votes
3answers
43k views

Noise and what does V/√Hz actually mean?

Noise figures in (op amp) datasheets are expressed in V/√Hz, but Where does this unit come from? Why the square root? How should I pronounce it? How should I interpret it? I know lower is better, ...
38
votes
8answers
19k views

Why do microcontrollers have so little RAM?

Maybe this is more of a perceptional problem, but it seems like microcontrollers have advanced by leaps and bounds in the last 20 years, in almost all regards, higher clock speed, more peripherals, ...
37
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11answers
3k views

Is there a dual of the transformer?

Capacitors and inductors are duals of each other. A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?) Also, you can vary ...
26
votes
3answers
17k views

Why is the Nyquist data rate lower than the Shannon data rate?

In the book Computer Networks, the author talks about the maximum data rate of a channel. He presents the Nyquist formula : C = 2H log\$_2\$ V (bits/sec) And gives an example for a telephone line : ...
21
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7answers
24k views

Where does U for voltage come from?

I believe in Europe the letter U is commonly used for voltage in (eg.) Ohm's law \$U = I × R \$. I think I understand where the letter V came from, commonly used in North America. But what's the story ...
20
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7answers
61k views

When people talk about a device “drawing” current, what do they mean? Why do devices under load “draw” more current?

In my (extremely rudimentary) understanding, the amount of current flowing in a circuit is determined by a) its resistance, and b) the voltage of the power source (voltage from beginning to end), ...
18
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5answers
2k views

In theory, is it possible to make a logic gate that uses zero current?

CMOS greatly reduces the current draw of ICs because one of the complementary FETs is always in the non-conducting mode, so there is only a flow of current during the transition between states, which ...
17
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6answers
2k views

Do electrical devices “take what they need”

One concept of electronics I have a hard time understanding is if things like motors, actuators, solenoids etc. use as much power as they need or what you give them. If a motor needs 12 volts and ...
14
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7answers
3k views

Why do LEDs have a maximum current?

So I understand that LED's have a maximum current (like 20mA for instance), but scientifically why is this? Using the water analogy it seems like a high voltage would be the thing that would mess up ...
11
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5answers
25k views

RC differentiator circuit explaination

This is the circuit of a basic RC differentiator, with the input/output voltage waveforms. First of all, I don't understand why there is decrease in the output voltage (discharging of charge from ...
10
votes
3answers
569 views

Is electronics driven by scientific papers?

Is electronics driven by scientific publication, similar to other academic fields? Two famous publications I came across, Gordon Moore's seminal paper, and Leon Chua's discussion of the memristor, did ...
10
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3answers
11k views

Magnet that needs power to turn off? Inverse coil?

I have never heard of such thing. But it would really suit my needs. I'm inventing a device and during it's operation, it should be able to catch an iron object any time (with a permanent magnet). ...
10
votes
6answers
6k views

Are E and B fields in phase in electromagnetic radiation?

I recently wrote this answer, in which I said: Radio waves are electromagnetic radiation. Electromagnetic radiation contains of two components, one electrical and one magnetic. These components ...
10
votes
1answer
2k views

How serial resistors actually reduce EMI?

I am recently working with a GSM based system, and there was this advice in the datasheet of the GSM module: 22 Ω resistors should be connected in series between the module and the SIM card ...
10
votes
3answers
2k views

How does control theory apply to my real-world processor-controlled boost converter?

I have a limited understanding of control theory. I dealt with poles and zeroes and transfer functions in school. I've implemented several microprocessor-based control schemes for DC/DC converters. ...
9
votes
4answers
19k views

Theory question about “j” imaginary unit (AC circuit analysis)

I have just started to learn about AC network analysis and have some questions about "j" (or "i" on my calculator), the imaginary unit. My book doesn't go into a great deal about this, and jumps ...
8
votes
3answers
57k views

What does common mode voltage stand for in an instrumentation amplifier?

I was reading a text about instrumentation amplifiers. I couldn't find any easy explanation what really common mode voltage means and its importance.
8
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3answers
14k views

How do I decide whether to use Kirchhoff's Voltage Law or Kirchhoff's Current Law?

When I solve questions, I usually get confused between when to use the Kirchhoff's Voltage Law (KVL) and when Kirchhoff's Current Law (KCL). Please help.
8
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2answers
1k views

What if you put a capacitor betwen the plates of another capacitor?

Based on: Is there a dual of the transformer? The picture of the capacitor inside another capacitor seems viable to me. If a transformer is two inductors with a common magnetic field, its dual would ...
7
votes
8answers
760 views

Does a radio station main amplifier work at the speed of light?

I'm having an argument with a classmate and we can't agree. He tells me that it's not possible for the amplifier of a radio station to amplify the input signal "instantaneously" (at the speed of ...
7
votes
3answers
2k views

How do I really calculate these resistors?

I am learning about it. I would like to focus on this circuit I am trying to calculate R10 and R11. I want Ic = 10 mA. Transistor is 2N2222A. This is an amplifier. If I understood how amplifiers ...
7
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2answers
1k views

Estimate capacitor parameters

I am thinking of making a capacitor, just for fun/for studying purposes. And I thought of the following exercise. In my local store, there exists rolls of polyethylene food film and aluminium foil. ...
7
votes
2answers
1k views

What is a mutator?

I'm reading this paper by Chua on the memristor. He claims that Using a mutator, a memristor with any prescribed phi-q curve ...
7
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3answers
3k views

Are TRIACs symmetrical?

When debugging a circuit using a micro-controller and triac to control AC current I ran into an issue (the triac wouldn't switch off) that was only resolved by flipping the polarity of the triac. The ...
7
votes
3answers
9k views

Why isn't a transformer a short circuit?

I'm a newbie with electronic components and I never fully understood why transformers, while essentially being a short-circuit from a wire perspective, don't act like short circuits (i.e. they don't ...
7
votes
2answers
1k views

Why do op-amps keep amplifying?

I was reading an old copy of Horowitz and Hill's The Art of Electronics and I am trying to wrap my head around operational amplifiers in negative feedback circuits. As the book explains, as the op-...
6
votes
5answers
6k views

Why pulsed DC passes through a capacitor?

OK, the current flowing through a capacitor equals C*dV/dt, I'm aware of that. What I don't understand is the physics of the process: why does a capacitor pass pulsed DC (0-10V for example) when ...
6
votes
1answer
4k views

Caculating baud rate of Ethernet per wire

I'm trying to find the answer to what should be a simple question. How do I calculate the physical rate bits are transmitted on an individual Ethernet wire? I am interested specifically in 100 Mbps ...
6
votes
4answers
2k views

Physical properties of transformers

In class, we were given equations for the transformer in terms of number of turns primary/secondary and coupling coefficient K, however effect of distance between coils, presence/absence of core, and ...
6
votes
3answers
313 views

Grokking oscillators

Can someone explain to me / point me to a good explanation of the theory behind an electronic oscillator? The Wikipedia entry explains what, but not how, which is what I need to know. TIA.
6
votes
3answers
664 views

Control theory: is there any actual application for D in ABCD matrix?

Recall that a LTI state space of a dynamical system is given as: Is there any actual purpose for D in the output equation? If D was not zero, it would mean that the output is "directly" dependent ...
6
votes
4answers
485 views

Another question concerning transistors

I know it's been asked 1,000,000 times how/what/why transistors work and I feel like I've read every answer but I still struggle with the basics. The struggle for me is the difference between ...
5
votes
2answers
2k views

Can an electric circuit do recursion?

Can an electric circuit do recursion? By recursion I mean any kind of recursion, tail, binary, nested, etc: http://www.sparknotes.com/cs/recursion/whatisrecursion/section2.rhtml By electric circuit ...
5
votes
1answer
828 views

What are the technical challenges to store electricity from lightning strikes? [duplicate]

I ask myself that question every time I watch a Tesla documentary. So, let's get some answers down so the smart ones can think about it and we can clean-up our environment. There is free electricity ...
5
votes
4answers
14k views

How to calculate a current being drawn by a full wave rectifier diode bridge?

I've been studying power supplies and diodes, all books I've read discuss a great deal of things, but there's something I haven't found, and that is how to calculate how much current a bridge ...
5
votes
2answers
2k views

Average Fanout of Non-Clock Nets

Xilinx ISE Design Suite gives information about the resources that a particular design uses. One of the parameters that is given to measure the estimated resources is "Average Fanout of Non-Clock Nets"...
5
votes
2answers
328 views

Voltage divider ambiguity

considering the following circuit : ...
5
votes
2answers
256 views

Why is this a 7th order circuit?

This is the circuit: I saw it in a book. It said that this is a 7th order circuit. From theory we know that the order of linear passive circuits is determined by the sum of capacitors and inductors, ...
5
votes
2answers
667 views

Why is flux-linkage a fundamental circuit variable?

In his paper Memristor - The Missing Circuit Element, Chua theoritizes the memristor based on observations relating to what he calls the four fundamental circuit variables, namely, the current <...
4
votes
3answers
16k views

What does E mean in this instance?

On all about circuits I keep seeing E in tables like this: In the table I and R make sense with the units. But the E doesn't. So where does it come from? I was looking at this article on ...
4
votes
7answers
2k views

What makes a circuit digital?

I've been trying to understand how a circuit becomes digital. I understand the different between an analog signal and a digital signal, but I don't see where digital circuits come from if all the ...
4
votes
1answer
411 views

Is there any relationship between frequency of signal and distance it travels?

I'm currently researching 5G technology. Many videos/articles on this topic claim that 5G is designed for communicating on lower distances (than 4G), because of higher (than 4G) frequency. So to build ...
4
votes
6answers
664 views

What's the rationale behind these warnings about extension cords?

(Disclaimer: I've read the help center and I do understand that this is bordering on off-topic since it's about consumer devices. However I hope that I've managed to make enough on-topic by asking ...
4
votes
2answers
3k views

Does perfect insulation exist?

In hydraulics, I think perfect sealing is achievable - it is not science fiction to consider a material whose pores are smaller than a water molecule (or is it?), which would yield zero flow rate. ...
4
votes
3answers
218 views

A few questions regarding B/E-fields in practical circuitry

I have been trying a few learning resources to help unlearn some of the notions that electrons flow through as energy. Chiefly this resource is what I have used: Amasci - IN A SIMPLE CIRCUIT, WHERE ...
4
votes
3answers
755 views

what is a thyristor

As part of my 2330 lv3 am required to know about thyristors. I just want to confirm my understanding is correct. A thyristor is basically similar to a transistor, only it stays switched on when it's ...
4
votes
2answers
780 views

Differential equation into circuit and back - good book

I have had some electronics, but we only built our circuits and then measured the input / output signals with oscilloscopes... Today I found an interesting question on physics stackexchange where ...
4
votes
2answers
422 views

Physically lightest topology for SMPS?

I'm being vague about part of my project, but please ask me to fill in critical details I'm missing. I need to power a 24V @ 20A device for 5 hours (one time), within a weight budget of 700 grams, at ...
4
votes
1answer
279 views

Help with AC circuit theory problem

I need help with the following AC circuit problem: Given the circuit (attachment 1) with known data: $$\underline{Z_3}=200(3-j4)\Omega$$ $$\underline{Z_4}=100(3+j20)\Omega$$ $$\underline{Z_5}=100(3+...