# 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

43 questions
Filter by
Sorted by
Tagged with
62k 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 ...
62k 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.
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 ...
22k 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, ...
20k views

### Capacitor Discharge through Constant Current Source

I was just thnking of how to model the voltage decay from a fully charged capacitor through a constant current source (CCS). A good approximation to this would be to model the constant current source ...
215 views

### How can Ohms law be used to calculate the resistor value for an LED when multiple voltage/current pairings give the same resistance?

Say I have a 9V supply, and I want to power an LED that requires 3V and 0.02A. From what I understand, I need to add a resistor that will drop 6V, and reduce the current to 0.02A, and I can calculate ...
61k 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, ...
4k 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 ...
32k 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 ...
8k views

### Is there a formula to determine the size of decoupling capacitors? [duplicate]

I have used many decoupling capacitors in circuits and have seen them in many textbooks, but they never give an explanation about why they picked a certain size of capacitor. Everyone seems to have a ...
74k 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), ...
8k 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 ...
2k views

### Why are dependent sources not disabled with the superposition principle?

I've been wondering this recently. My intuition says that a voltage drop across a dependent source is no different than any other circuit element whose response depends on the inputs of one of the ...
519 views

### Why earth ground connection does not leak current?

This seems like a question which has been asked multiple times on forums. I researched the problem but I still was unable to figure out the answer which I can at least intuitively understand. So in ...
2k 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 ...
1k views

### Current divider rule calculation issue

I'm doing the exercises from Wisc-Online. This one I think they are really great to learn and practice and have already done a bunch of their practical trainings. But here I'm starting to be crazy. I ...
19k 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 : ...
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. ...
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 ...
27k 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 ...
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 ...
2k 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 ...
15k 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 ...
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 ...
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-...
5k 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 ...
527 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 ...
1k views

### Does electricity always flow in a closed loop and why does current flow to ground?

I have been taught that current flows in a closed loop back to the source. And with electrical distribution, current flows to ground because the whole grid is effectively grounded back to the source. ...
2k 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 ...
12k views

### Why is the Ampere the only SI fundamental unit for electricity?

According to wikipedia the only SI fundamental unit for Matters Electrickal is the ampere. Don't you at least need the ohm to derive anything? How would you make volts from only amps? Perhaps I ...
4k 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. ...
75 views

### Why does lumped discipline not hold as dimension approaches operating signal wavelength?

I'm studying some basic introduction to the lumped matter discipline on my own. I completely understand where the first two constraints come from (i.e. lumped matter can only interact through their ...
815 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 ...
568 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 ...
15k views

### How is quasi peak calculated

As said in the headline, how is quasi-peak calculated? I was not lucky on google this time, so I will ask here. I'm just looking for the formulas behind the calculation, since I want to make some ...
3k views

### Discharging a capacitor through a resistor and an LED in series

Suppose you have a capacitor of capacity $C$ and initial voltage $U_0$, a resistor $R$ and a LED with threshold voltage $U_S$ ($U_0 > U_S$) in series. Now I want to calculate duration \...
472 views

### A question about electrons, charges and current

Let's talk about DC, a very simple circuit: a light bulb and a battery. Some authors say that electrons move from negative to positive and current from positive from negative. I always thought ...
396 views

### Must the characteristic impedance of a transmission line be non-real for it to be lossy?

In Does conductance in the transmission line model represent a physical quantity? it came up that a non-real characteristic impedance just means the line has some loss. With real transmission lines ...
4k views

### Norton's and Thevenin's theorems importance

Are Norton's and Thevenin's theorems used in real life? And in which situations? I'm reading a circuit analysis book and I asked myself: do electrical engineers use these theorems to get current and ...
898 views

### Understanding microphone sensitivity

My goal is to figure out a relation between output voltage and input SPL: $$dB(SPL) = f(V_{out})$$ First, I get the sensitivity in volts from this formula: Sensitivity_{dB(V)} = 20 * log_{10} (...
453 views

### Modelling transistor V_be and bulk resistance

I'd like to calculate algebraically the DC behaviour of various bipolar transistor circuits that used matched pairs or quads (exponential converters, current mirrors etc.), taking into account the ...