Questions tagged [physics]

Physics is the natural science that involves the study of matter and its motion through space and time.

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2 votes
1 answer
38 views

Can a vacuum tube convert tube heat to power

In playing with the triode component in the Falstad simulator, I often observe behaviors that seem nonsensical, with a tube sometimes acting as a power source. If a triode just had three connections ...
-1 votes
4 answers
96 views

Why do electrons move in a circuit? [closed]

I am trying to make sense of why electrons move in a circuit. I did my research and the first answer I got is because of the difference of electric potential between the two points of the battery that ...
2 votes
1 answer
244 views

Isolated circuits: can their reference voltages (GNDs) be at the same potential?

Suppose there are two independent circuits isolated from each other. If they are isolated, the impedance is very high between them (ideally infinite) and there is no current flowing from one to the ...
1 vote
1 answer
65 views

Limit of applicability of "quasistatic"/capacitive picture of devices

When analyzing the transitories associated with switching in semiconductor devices, in textbook treatments one often sees the time dependence considered by including (potentially nonlinear) capacitors ...
2 votes
1 answer
92 views

LC Resonance with Inductor with Solid Metal core

Consider inductor with air gap and solid metal core made from material with relative magnetic permeability 1 regardless of temperature (such as copper or aluminium). There is Air gap between coil and ...
5 votes
1 answer
394 views

What is the correct carrier concentration equation to use?

In this book I am reading, it gives the intrinsic carrier concentration as: \$ n_i = \sqrt{N_c\cdot N_v} \cdot e^{({\frac{-E_g}{2*K*T}})} \$ While another book says the carrier concentration is: \$ \...
0 votes
2 answers
97 views

RC response for any given voltage [closed]

Lets imagine a simple RC circuit in which the response voltage is defined by the following equation: $$ V(t) = V_{inf} \cdot (1-\exp(-t/\tau) $$ This is only true when a constant voltage is applied (...
6 votes
5 answers
13k views

Designing an analog circuit that Fourier Transforms or Laplace Transforms an input signal

This is currently my pet project but I am a bit stuck on some problems. First I'll go over my idea for the Fourier Transform: The Fourier Transform is defined as \$F(\omega)=\int^{\infty}_{-\infty}...
0 votes
2 answers
410 views

Electric potential energy of charge relative to 2 metal plates

Let’s say I have a positive electric charge in middle of two plates, one is positively charged, the other one negatively with total intensity of electric field of 5 N/C. If the charge has 2 Coulombs, ...
1 vote
0 answers
204 views

How does a boogie board/LCD writing tablet/ChLCD reset actually work?

there are those boogie boards, which essentially are just special LCD screens: ChLCD screens. which work by reflecting light on the places where it is activated. in a boogie board, the pressure causes ...
2 votes
1 answer
219 views

What would be the effects of a -1000 nanotesla geomagnetic storm be on modern electronics?

After reading the Wikipedia article on geomagnetic storms, I'm curious about what the effects of a -1000-nanotesla-minimum geomagnetic storm would be on modern military and consumer electronics, as ...
1 vote
1 answer
86 views

Confusion about why pn junction discussion insensitive to doping variations faster than Debye length

Sze (Physics of Semiconductor Devices, 3e) gives the following discussion which relates to how equilibrium electric fields/equilibrium potential build-up at thermal equilibrium are related to doping ...
2 votes
1 answer
347 views

What is the length of one symbol sent through WiFI?

Having a WiFi emitter sending a frame, how much time does each symbol take? And therefore, what distance do they spread over? This depends on the Modulation Coding Scheme. I would like to know which ...
0 votes
2 answers
505 views

Capacitor discharge math discrepancy

I'm trying to cross check mathematically the mA being discharged from a .33uF capacitor which is charged to about 1200V by a circuit which is provided 37W of power to it. I do it three ways. 1) The ...
1 vote
1 answer
93 views

Does these terms consider the same: Voltage, electric potential, and potential difference?

What are the differences between these terms? Are they considered the same?
1 vote
1 answer
85 views

How to derive the maximum power transfer theorem using the relation p=v²/R?

In most derivations of the Maximum power transfer theorem the derivation is done using the relation of power : P = i²R And on further derivation it comes out to be Pmax = Vth²/4Rth If I derive the ...
1 vote
4 answers
1k views

Why don't volts and amps necessarily increase together in Watts = Volts*Amps? Don't more volts = more amps and vice versa?

I'm trying to understand modern American housing circuitry, which have 15 and 20 amp breakers and work on 120v circuits. They're described using the simple formula Watts = Volts*Amps. I'm using ...
1 vote
2 answers
80 views

Lightning board 3 meters

In France, you will see some signs like the one below: Those signs are next to buildings which have lightning rods. They also have some conductors to make the current go from the rooftop to the earth ...
1 vote
1 answer
56 views

Thermodynamics of a simple electrical conductor

I derived an expression for the time constant of the temperature of an electrical conductor and was looking for some constructive feedback. Initially there is no current flowing through the conductor ...
1 vote
2 answers
73 views

Why don't oppositely charged ends of separate batteries and capacitors produce current flow? [duplicate]

I have a question here regarding the flow of current from charges. I understand if you connect a simple circuit to a battery it creates surface charges which allow the current to flow. My questions ...
1 vote
1 answer
157 views

Construction of a Lagrangian function for a circuit

I was reading the paper "Introduction to quantum electromagnetic circuits", by U. Vool and M. Devoret and I am stuck in the construction of a Lagrangian function for the example LC circuit ...
3 votes
0 answers
178 views

Physics diagram to electrical schematic

After waiting a reasonable amount of time with no answer here, I have duplicated this question at Physics Stack Exchange. I am asking this question on behalf of user furious.neutrino. This question ...
1 vote
0 answers
412 views

Calculating steady-state temperature for electrically heated wire

I am working on a program aimed at finding optimal parameters (voltages and feed rates) for a hot wire foam cutter. One starting problem that has to be solved before even attempting to evaluate heat ...
0 votes
1 answer
710 views

Given a energy band diagram, can you always calculate potential, electric field, and charge distribution?

Given a band diagram, where do you start to get the electric field and charge distribution?
3 votes
2 answers
996 views

Why is erasure much slower than write for (NAND) flash?

Typical block erasure time for NAND is on the order of milliseconds which is one order of magnitude higher than write. Both of them are based on FN current. Why? Thank you!
0 votes
0 answers
34 views

Sizing MOSFET VDS to account for Stepper Back EMF

I'm having difficulty conceptualizing how the Back EMF of a motor, stepper in this case, can damage an H-Bridge MOSFET if the Vds aren't sized correctly. My main issue is my understanding of how the ...
1 vote
3 answers
68 views

Seebeck Voltage [closed]

I understand that the voltage of two metal elements is V=(Sb-Sa)(T2-T1) regarding a thermocouple. But, what if mass was introduced to find the voltage? Can mass also be used to find voltage with ...
1 vote
1 answer
92 views

Transient Charge Density in Conductor

Veritasium's (Derek Muller's) video How Electricity Actually Works makes the claim at 4:44 that: The truth is, if you average over a few atoms, you find the charge density everywhere inside a ...
3 votes
1 answer
4k views

Hall effect sensor operational distance from magnet

I want to use a this hall effect sensor to detect the presence of magnet. I'm pretty sure I understand how to use the hall effect sensor, but I'm not sure how to calculate the distance the sensor can ...
0 votes
1 answer
394 views

How to analyze a capacitor connected to a DC voltage directly (no resistor)?

This may be a very basic question but my misunderstanding is due to the difference between how physics explains the charging of capacitors and how we analyze circuits in circuit analysis. According to ...
1 vote
1 answer
325 views

Understanding the formula of the saturation current in a PN-junction diode

According to Wikipedia, the saturation current in a diode is given by the following formula: $$I_S = qAn_i^2\left(\frac{1}{N_D}\sqrt{\frac{D_p}{\tau_p}} + \frac{1}{N_A}\sqrt{\frac{D_n}{\tau_n}}\right)$...
3 votes
3 answers
727 views

What does it mean that an integrator has an infinite DC gain?

I mean, I get that, in the ideal case, \$G\rightarrow \infty \text{ as } s \rightarrow 0\$, but it doesn't make sense for a physical device to be able to amplify a signal to an arbitrarily large value,...
0 votes
0 answers
26 views

How to find gain parameter of complementary filter algorithm for application in navigation

I am using mpu-6050 6 axis Inertial measurement Unit for navigational purpose for tracking orientation and position of a vehicle w.r.t starting point, I am trying to improve the orientation tracking ...
1 vote
2 answers
121 views

How does electricity flow if circuit is not complete? [closed]

https://youtu.be/oI_X2cMHNe0 What is he saying at 13:20? How can bulb glow if the circuit is not complete?
0 votes
2 answers
134 views

What is happening at the end of this circuit? Why is the voltage zero at the bottom?

What is happening to the voltage at the bottom? Why is it zero? How does the voltage go back to the positive terminal?
0 votes
1 answer
41 views

Fundamental Question - how does magnetic permeability work for weak signals?

This is basically a physics question. If a sophisticated answer is needed, please go for it. The standard explanation of magnetic permeability is something like this: In a ferromagnetic material, ...
0 votes
0 answers
22 views

What is the relation between the minority charge profile in the base and the collector current (BJT)?

For a BJT in forward active mode, the minority charge concentration at the base-collector junction is zero. If this is the case, how is a non-zero number of electrons able to make it to the collector? ...
0 votes
0 answers
69 views

What goes on inside the transistor that amplifies the signal?

I understand that, for example, in BJT NPN transistor in common emitter configuration used as amplifier, feeding the small signal at the base will produce the larger signal at the collector. But what ...
4 votes
1 answer
549 views

Does electricity flow in open circuits?

Say I have an open circuit with a battery. I have a wire connected to the negative terminal and a wire connected to the positive terminal. The wires aren't connected. In this scenario, would their be ...
1 vote
0 answers
59 views

Igniting and maintaining plasma in low pressure chamber

I'm trying to create and maintain plasma inside a vacuum chamber (up to 50 Pa), I have a home-made feedthrough done with an HV BNC sealed with Viton gaskets on a KF50 flange (makes a ≈25 mm gap). I ...
8 votes
3 answers
1k views

Do MEMS or optical gyroscope record Earth's rotational and revolutional angular velocities?

I am using a 3 axis gyroscope (Android device) to record angular velocities using a sensor data logger application. When the device is placed stationary, the gyroscope recorded the following values: ...
6 votes
3 answers
7k 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 ...
1 vote
1 answer
337 views

Equation for diode saturation current in photovoltaic cell model

I've been looking for mathematical models for photovoltaic cells. Most of the references I've found use the following circuit to the model the behavior: Particularly, the diode current is modeled ...
3 votes
1 answer
198 views

What is equilibrium carrier concentration in a semiconductor? Is it material specific? How to calculate it?

Is equilibrium carrier concentration dependent on doping density? If it is, then how to know how much the doping density should be for a particular semiconductor device?
8 votes
1 answer
195 views

Is birefringence exploited or otherwise meaningfully observed anywhere in electronics?

Birefringence is a property of certain materials where the refractive index of the material is dependent upon the polarization and direction of propagation of light through it. I recently learned ...
1 vote
1 answer
260 views

How does the electric field inside a conductor remain zero?

I'm learning about current in conductors, and came across the statement that "The electric field inside a perfect conductor is zero", this is frequently explained used Gauss´s Law by saying ...
2 votes
2 answers
845 views

Why does the majority carrier concentration near the junction not decrease under forward bias? (PN junction)

We see that the current due to the majority carrier decreases near the junction as shown above, which means the majority carrier concentration should also decrease since the diffusion current is given ...
3 votes
1 answer
222 views

Will thermocouples sharing a common wire create inaccuracies during measurement?

Specifically, I've been working with pre-existing temperature cables which are T-type thermocouples which share the same Constantan wire. My question is if one of the thermocouple junctions is heated ...
90 votes
19 answers
25k views

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

simulate this circuit – Schematic created using CircuitLab My physics teacher said that the current through the resistor is 4A because each battery has a current of 2A if hooked up to the ...
2 votes
2 answers
202 views

Static electricity discharge, what gets transfered?

Ive been studying Maxwell equations at school and I solved several excercises regarding electrostatic fields, however, I still have some very basic unanswered questions: When a non conductive object ...

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