# Questions tagged [electrical-engineering]

The engineering discipline concerned with the study, design and application of equipment, devices and systems which use electricity, electronics, and electromagnetism.

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53 views

### Powerlines in Asian villages are they safe? [closed]

Powerlines in Asia - I have seen lots of lines wound up or passing through bushes. Is this dangerous? How does this work?
95 views

### Will the electrical potential difference between the Windward and Leeward sides of a mountain range generate electrical current?

I would like to know if it is possible that the electrical potential difference between the Windward side and the Leeward side of a mountain range, due to a thunderstorm occurring on the Windward side,...
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### Can we catch signals from a cellphone using an external device? [closed]

What if someone stole em waves from our mobile devices to listen to our conversations or get our OTP. Whatever encryptions they have they are just EM waves innit and they cannot be propagated only in ...
1 vote
21 views

### Calculate optimal spacing of vertical magnetometer configuration in Magnetic Ground Survey

I have a vertical magnetometer configuration, and measure lines on the ground. I want to calculate the optimal spacing, based on the interpolation between the lines. Applying the generalized ...
44 views

### Why electric field increase near the cable connected in AC 220V socket even current is zero?

If I put low frequency electric field meter near the connected cable in AC 220V socket, he show 1200 V/m even if device is turn OFF(zero current), if disconnect cable from socket, field drop to 8 V/m. ...
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61 views

### Why do lamps in circuit have potential difference but two points in cable without anything in the middle of it have no potential difference?

I'm preparing for my EE major, this is my starting point.
1 vote
104 views

### Deriving the Cable Equation from Maxwell's Equations

My goal is to reach equation 12 on this wikipedia page: Cable Theory. The demonstration is usually done by making an infinitesimal circuit, but I would like to get there via Maxwell's Equations by ...
123 views

### Can aluminum shield magnetic fields?

Say I have built a simple working AC 50 Hz transformer. It has copper coils at each end of a soft iron rod. If I slip an aluminum tube over the soft iron rod, so the copper coils now are over the ...
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1 vote
44 views

### Back EMF in electromagnetic coil

I am trying to quantify the back EMF generated while actuating an electromagnetic coil, this would be included in a general calculation to estimate the coil output under a variety of conditions. My ...
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36 views

### Is there any electronic devices that maintain charged state?

I want to know how to make electronic devices that are continuously charged to + or - state on which surface when voltage is applied to utilize the dielectric polarization property, or if there are ...
62 views

### I don't really get transistors. How do they work exactly in the active region?

So in an NPN transistor, when the base-emitter is forward biased, and the base-collector is reversed biased, electrons from the emitter get to the base. That part I understand, electrons are the main ...
34 views

### Built-In Potential (Forward vs Thermal Equilibruim)

According to my book the built-in potential $V_{bi}$ for a PN junction under thermal equiliubrium is: $$V_{bi}= \frac{KT}{q}In(\frac{n_{no}p_{po}}{{n_{i}}^2})$$ where $n_{no}$ and $p_{po}$ are the ...
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47 views

### Why is potential continuous at dielectric conjunction?

Lets take for an example, a spherical capacitor with two dielectrics. The Electric Field will then be given by $$\frac{Q}{4\pi\varepsilon_0\varepsilon_r r^{2}}$$ We know that then the electric field ...
1 vote
26 views

### How do I calculate thrust for a high bypass turbofan engine? (7th grade) [closed]

so i'm a 7th grader trying to create something using a high bypass turbofan engine but I need to learn how to calculate the thrust for it and i'm unsure on how I am meant to do that. If anyone has any ...
1 vote
171 views

### Does resistance of a rheostat affect current in the circuit?

This is the typical experimental setup to determine the unknown resistance of a given wire. As we move the sliding contact of the rheostat, we get different values of voltage and current. a plot of V ...
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### Charge moving in an electric field and magnetic field? [closed]

lets say I have an electron moving towards an oppositely charged plate. Perpendicular to the electrical force vector, exists a magnetic field. How would I calculate the force on the electron? Like ...
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36 views

### Resistance in series also slows current down so why is resistance connected in parallel in galvanometer ammeter and not in series?

When we convert a galvanometer into an ammeter we connect the resistance in parallel, the only reason we connect a resistance in parallel with galvanometer is so less current passes and the flow of ...
38 views

### For intrinsic semiconductors, is the gap Energy equals $E_c-E_v$ or $E_c+E_v$?

So I have a problem with the intrinsic Fermi Level because by definition it is in the middle of the gap energy, and knowing that Eg=(Ec-Ev), we should have Ei=(Ec-Ev)/2. But when we follow the ...
49 views

### How a switching mixer works in this example circuit?

I am reading about lock-in amplifiers and came across this example circuit of a mixer: You have one sinusoidal input signal $e_1$ with a phase $\phi_1$ and the local oscillator has a square-wave ...
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1 vote
62 views

### EM wave emission from earphone wires due to varying current signal

if we listen to some audio signal on a wired earphone, then does the wire of the earphone act as a transmitter antenna to emit the audio signal as radio waves even though its strength might be ...
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37 views

### How is gradient magnetic field generated in MRI scanner, considering 0 divergence

During the phase and frequency encoding process of MRI scanner, gradient field with a gradient is applied along the direction to change kx and ky of spins at different spatial location. I am confused ...
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76 views

### Saturation region of common emitter BJT

About the saturation region of common emitter Bjt it's written that In saturation mode both of the "diodes" in the transistor are forward biased. That means V(BE) must be greater than 0, and ...
• 1,441
38 views

### When forming an n channel in an N MOSFET, do the pn junctions of the drain-substrate and source-substrate parts disappear?

When forming an n channel in an N MOSFET,, do the pn junctions of the drain-substrate and source-substrate parts disappear? Here's what I expected: When gate voltage (higher than threshold voltage) ...
• 107
135 views

### What is the "closed circuit" of a bug swatter racket?

There are bug swatter racket that can kill fruit flies, mosquitos, or flies, if the insect touches the metal mesh. However, when I look at the construction of the device, the metal mesh is all one ...
50 views

### Is the direction of base current always constant in a BJT transistor?

Is the direction of base current always constant in a BJT transistor? Excluding the transistor breakdown state, is the direction of the base current always the same in the four modes: active mode, cut-...
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155 views

### Voltage across the diode?

Why the voltage across an ideal pn junction diode remains 0.7 volts, even when the applied voltage exceeds 0.7 volts? Shouldn't it be the applied voltage minus the 0.7 V?
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185 views

### What can cause a spot above my WiFi router's antenna? [closed]

Lately a weird dark spot has appeared right above the antenna of my wifi router. It wasn't there before. I have tried to wipe it and it got a little bit brighter but I don't think it's dust. My guess ...
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93 views

### How does an antenna work?

I'm looking for a model of an antenna that would explain how it works an in particular where the values of impedance like 36.5 ohms come from. I've tried looking but everything i found was overly ...
31 views

### Mesh current analysis but with variable resistors [closed]

I can't seem to be able to introduce V0 here! Here was my working out, using 3 mesh and 4 node equations. Only one mesh equation has V0 but it doesnt seem possible to introduce it into the rest.
68 views

### Why we are using coupling capacitor in AC amplifier? [closed]

Why we are using coupling capacitor in AC amplifier?
84 views

### Magnetic force acting on a current loop while next to a current carrying wire

With I1=20A and I2=30A, find the net magnetic force acting on the loop. I am not sure how to even approach this problem. I know that the magnetic field of the wire is $\frac{\mu_0I}{2\pi r}$ and that ...
• 1
41 views

### If we change the direction of the connections in a step-down transformer, will it become a step-up transformer?

If we change the direction of the connections in a step-down transformer, will it become a step-up transformer?
27 views

### Why my DC thick charging cable is slower than a thinner one? (having same power rating & adaptor)

Does that means thick wire cause more current loss than thinner one?
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### How are quantum gates encoded in voltage/current waves for superconducting qubits?

From what I understand, the voltage and current waves propagate down the input transmission line, hit the nonlinear oscillator, and then bounce back toward the generator. How are gates such as the X ...
8k views

### How do computers store sound waves just by sampling the amplitude of a wave and not the frequency?

All of this just doesn’t make sense though. I mean, doesn’t the amplitude represent the loudness and the frequency the pitch? Aren’t they completely independent from each other? Is the book just ...
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52 views

### Power dissipated in transmission cable

Taken from NSAA/ENGAA 2022 (University of Cambridge's admissions assessments for Natural Sciences/Engineering) Electrical energy is transmitted at high voltage to a remote farm using an overhead ...
193 views

### Resistors in high frequency

My question is this: Can we use ordinary resistors like those we use in labs(1.2K ohm), in high frequency (like 4GHz)?
400 views

### How are photodiodes fundamentally calibrated?

I have a theoretical question regarding the irradiance measurement of light sources. From the basics I know the following: Irradiance has the unit $\frac{w}{m^2}$, in the context of light that means: ...
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179 views

### Working of transistor

For the operation of the transistor, the base-emitter junction is forward-biased and the Base collector junction is reversed-biased. Due to the concentration gradient, electrons from the N side (...
96 views

### Why Faraday homopolar generator need brushes?

It is said that if one would attach a load physically to the rotating disc from center to rim no current would flow because both in the load wires and the disc itself currents would be generated in ...
93 views

### What is "capacitive effect" in terms of battery research?

For example, the paper I am reading states that the current was "periodically interrupted without changing polarity" to "demonstrate that the peaking behavior is not due to a capacitive ...
70 views

### Help understanding why built in voltage in PN junction created?

I was reviewing basic semiconductor physics and need some help understanding where my logic is incorrect. For a basic PN junction, the process of forming the depletion region is described as follows: ...
70 views

### Doubt on time invariant system

Now I am delaying the output of a system (which takes $x \left( t \right)$ as input and gives $t \cdot x \left( t \right)$ as output) by $T$ then final output is: Let's denote the output of the ...
72 views

### Why there is no EMF induced in this circuit

Why there is no current flow in this circuit? On this diagram, the copper wires are long and extend far beyond the magnetic field range and they rotate with multimeter or BT transmitter, magnet is ...
72 views

### From the physics standpoint, how should I align a USB Internet stick relative to the nearest cell tower in order to have the best signal? [closed]

I use this USB Internet stick: (Huawei E3372h-153) To connect to the Internet, I simply insert a SIM card into this stick and then insert the stick into a USB port of my laptop. Based on my ...
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764 views

### Load Lines and Characteristic Curves

While studying electronic circuits involving diodes, I came across the concept of characteristic curve, which relates the voltage drop in a diode with the current through it. However, I was also ...
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### Why do we still consider a doping concentration in undoped MOSFET devices?

I am studying cryogenic behaviour of MOSFET devices especially the evolution of threshold voltage with temperature. I mostly measure FinFET and FDSOI devices, all which have supposedly undoped channel....
94 views

### How to collapse telescope image cone into an optical fiber?

I have an application where a telescope will be receiving light from a laser source. I would like to couple the output of the telescope, which is the image cone, into an optical fiber. Does anyone ...
92 views

### Does KVL don't hold in pn junction reverse bias?

Does KVL hold in pn junction reverse bias because any reference about semiconductor physics provide that figure if we apply KVL around the loop won't be zero it will be equal to $V_{bi}$ then how KVL ...
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1 vote
under thermal equilibrium the pn junction have a built-in field let say it's $E_{1}$ , if we make a reverse bias the external battery provide a permanent field $E_{2}$ , so the total field inside the ...