# 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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### Why is the gradient of Energy vs. wavenumber(k) zero at the edge of Brillouin zones?

My question relates to semiconductor physics. The relationship between energy E and wavenumber k for the Kronig-Penny model looks like this, where a is the period of the potential function: I am ...
2answers
57 views

### Bipolar Transistor Inverter Circuit Analysis

I have been trying to understand this question and I'm just not sure what equation to use for the collector current. I'm not sure if I need to be using an output voltage function of time? All I have ...
5answers
4k 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 ...
5answers
148 views

### How can I describe and explain SMPS on a very basic level without diving down in heavy maths / EE lingo?

I'm writing a book about repairing electronics. The audience level for the book is "very little knowledge about electronics" and it's mostly about the mindset and mindtools for finding problem sources ...
1answer
375 views

### Parallel RLC Resonance bandwidth

Good day ,I need help in understanding a practice problem that my professor gave us. A parallel resonant circuit has Q = 20 and is resonant at ωO = 10,000 rad/s. If Zin = 5kΩ at ω = ωO what is ...
3answers
188 views

### Is space division multiplexing really multiplexing?

I don't know much about electronics, but happened upon the Wikipedia article for Multiplexing, which defined it as: a method by which multiple analog or digital signals are combined into one signal ...
4answers
77 views

### No potential difference between the negative terminal of battery A and positive terminal of battery B?

I know that if you have two batteries, battery A and battery B, and connect the negative terminal of battery A to the positive terminal of battery B, there is no potential difference. If you consider ...
1answer
413 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 ...
1answer
622 views

### Intuitive and iterative approach to understanding of blinking LED circuit

I've used following schematics to build blinking LED circuit and it worked. I tried to understand how it works qualitatively without solving differential equations. By this I mean understanding ...
4answers
117 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 ...
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. ...
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). ...
3answers
10k 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 ...
1answer
74 views

### Average Power for “Infinite period of time” of a periodic signal

Last night in class we talked about the average power for any periodic function. I'm just confused of why the one halves are in the bounds for this equation. Since we are letting tau approach ...
2answers
73 views

### current speed/flow [closed]

Note my questions are in form of explaining. its because I've scattered information (or assumptions) and it want to link them. that's probably why you can see me explaining to much? Question part: ...
2answers
420 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 ...
6answers
42k 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 ...
3answers
44k 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, ...
2answers
65 views

### What are the initial conditions used to find the coefficients in the current equations?

Suppose a RLC series circuit. R, L and C are in series with a battery and a switch. The switch is open. L and C are discharged. At t=0, the switch is closed and the battery (V1) feeds the circuit. I ...
1answer
126 views

### How do I find the current equations for the RLC Series Circuit?

Let's talk about a RLC series circuit. R, L and C are in series with a battery and a switch. The switch is open. L and C are discharged. At t=0, the switch is closed and the battery (V1) feeds the ...
1answer
210 views

### Degenerate circuit concept and its theoretical and practical implications

I came across with the term "degenerate circuit" when I was studying solving linear differential equations with Laplace transform. I have learned that a system is called degenerate when the ...
0answers
101 views

### When deriving the instantaneous power equation for an AC power system, I get different answers depending on how I model the V & I signals. Why?

When I define $v(t)$ & $i(t)$ like this: $v(t)=V_m\cos(\omega t)$ $i(t)=I_m\cos(\omega t-b)$ where $V_m$=Voltage Amplitude, $I_m$=Current Amplitude, $\omega$=rotational frequency,...
3answers
843 views

### How to calculate the input and output capacitors of a common emitter amplifier using BJT?

Sorry if the question is stupid, but my head is still hard as a coconut and I am learning... I am dealing with this circuit that I have calculated from scratch. This circuit was designed to have ...
1answer
49 views

### What are the differences between Greinacher and Bridge voltage doublers?

I was reading a wiki article on Voltage doublers, and wondered - what are principal diffirences between two following schemes: They all share same amount of components, but when and why should be one ...
2answers
69 views

### Help me understand what happens with the circuit when an AC signal is applied

Consider this circuit. Transistor is 2N2222A. Ic is chosen to be 10 mA. Hfe is 225 for that current. Resistors are calculated to have Vbe = 0.7V and Vc = 4.5V. I am trying to understand what happens ...
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 ...
2answers
53 views

### Does a current source have a difference in potential?

I am doing a nodal analysis of this circuit. I have found that $V_A = 10 V$ and $V_B = -20 V$ is it possible to have a situation like that? I mean a difference in potential between terminals ...
2answers
69 views

1answer
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### How do I calculate the unknowns of the current equation for a RLC series circuit?

Suppose I was dealing with the following voltage equation for the RLC series circuit: $v(t) = Ae^{m_1t} + Be^{m_2t} + V_s$ To know the values of A and B I would do the two initial conditions: ...
6answers
696 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 ...
1answer
58 views

### Trying to understand the transient current equation on a RLC circuit

I am reading this doc I see this magic happening on the third line of equations... How in the name of Math, does this $Ae^{st}$ appeared there? Magic?
1answer
104 views

### MCU sinking current from a higher voltage source

In previous designs, I have used an MCU digital output to drive the lower side of a resistor ladder to the supply voltage, to prevent power consumption when the ladder is not being sampled: Schematic ...
1answer
53 views

### Is this negative resistor model valid for any type of LC self oscillating circuit?

Is the following negative resistance model valid for any type of LC oscillator? If not, what are the exceptions? Image Source is from here
0answers
35 views

### Understanding generator wear and rotor electrical measurements

I have a generator that I am attempting to fix, and I am getting readings that are out of spec on the rotor brushes. Per some instructional videos I found, I should be measuring 5V AC on the rotor ...
3answers
657 views

### Simple transistor circuit

I have been studying transistors and decided to try my knowledge in my lab to find out that nothing works as I thought it would.. I had a small lamp 12V and a handful of 2N3904 transistors, along ...
2answers
161 views

### Electric networks with an open-loop

This is a generic concept question that I encountered during the first day of an EE course. Our lecturer told us that electric circuits are essentially electric networks with closed loops. I would ...
3answers
2k views

### Subthreshold regime advantages/disadvantages

Could someone explain the most important reasons for an analog designer to use MOSFET transistors in the subthreshold regime? What are the advantages and disadvantages? Generally, the circuits in mind ...
4answers
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 ...
1answer
83 views

### Deriving resonance frequency of RLCC circuit

I am trying to determine the resonance frequency of an RLC resonator with added capacitor, as shown below: simulate this circuit – Schematic created using CircuitLab Two cases are easy to ...
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, ...
2answers
204 views

### Does an LED’s free electrons ever run out?

I’m aware that LEDs are doped with impurities on each p-type and n-type material to increase the charge carriers of each semiconductor. My curiosity now is, how does each side continue to have extra ...
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 ...
1answer
279 views

### Basic Theory - finding voltage between two points

I'm a neophyte here trying to learn using "Practical Electronics for Inventors, 4th Edition" (which received almost a 5 star review with over 500 reviews on Amazon). The preface of the book states "...
2answers
449 views

### Should the error term of PID be normalized?

By "normalized", I mean +/-1 ~= the maximum error the system can reasonably be expected to experience, or divided by the setpoint. Background: I am working on a PID controller for an SSR heater ...
6answers
375 views

### What is the voltage potential of ground during a short

During a short, is it possible for the voltage potential of the ground to change? Say for example, we short a 9V battery, how does the ground stay at 0V and not become 9V?
1answer
181 views

### Step Response of Ideal Inductor with Current Source

I'm taking an electronics course to get a physics minor (I'm an applied math major) and today, the professor shows a diagram of an ideal current source connected to an ideal inductor. Crazy stuff I ...
2answers
95 views

### resistance and current [closed]

I struggle to understand how if I increase the resistance in a circuit, it requires less current, based of ohms law.
4answers
548 views

### Is a hole in a conductor the same thing as a positive ion?

The flow of current in a (semi-)conductor is often described as holes and/or electrons moving between atoms. In this context: Is an atom with a hole the same thing as a positive ion (cation), and Is ...