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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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Why galvo mirrors have different speeds? [closed]

I want to understand why galvo mirrors have different speeds for different axes for raster scanning in a traditional laser scanning confocal microscope.
anabelee's user avatar
2 votes
1 answer
92 views

Will a circuit oscillate at all its resonance modes or only the most dominant one?

Will a circuit oscillate at all its resonance modes or only the most dominant one? Consider an amplifier with a feedback loop that meets the Barkhausen criteria at multiple frequencies. Will it ...
SRobertJames's user avatar
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2 votes
2 answers
580 views

If electromagnetic waves are indeed created by a changing electric and magnetic field, then why don't we see magnet based antennas?

I understand that exciting electrons, basically freely moving electrons cause electromagnetic waves. The faster they accelerate the higher the frequency of the waves. If this is indeed the case, then ...
Vishwa Mithra Tatta's user avatar
9 votes
4 answers
2k views

Why does this battery use 4.2 V when its nominal voltage is 3.7 V?

I changed my headphone power circuit and I noticed it was using 4.2 V to charge a 3.7 V battery. I am confused why it is using 4.2 V. I know to charge a battery you need more voltage than its rating, ...
Ray's user avatar
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0 votes
1 answer
54 views

What is the reactive power of a capacitive circuit?

I want to understand the reactive power in a purely capacitive load. Surprisingly, I couldn't find the formula for this anywhere, so I derived it myself, and would like to ask 1. Is this formula ...
SRobertJames's user avatar
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6 votes
3 answers
228 views

Behaviour of uninitialised RAM in an ASIC

This is a question for anyone with experience designing or with a deep knowledge of volatile memory in an ASIC. E.g. chip designers or silicon process engineers. We are using the ET1200 EtherCAT ASIC (...
Rocketmagnet's user avatar
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3 answers
105 views

Why are current, voltage and resistance all low in this scenario?

My understanding here is that compared to the internal resistance of the source, the resistance of a human is very low so terminal pd is also low. Then if current chooses the path of least resistance ...
user357057's user avatar
15 votes
3 answers
2k views

Why does an inductor's inductance decrease with current?

I am struggling to understand what seems like a fundamental behavior of an inductor. I am looking at a chip mount LQM18PN2R2MFR inductor. One of the diagrams on the manufacturer's website shows a ...
tronhawk's user avatar
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2 votes
1 answer
138 views

Measuring current with a multimeter around a closed circuit [closed]

A question from physics lab: Referring to the circuit you built to measure currents, what would happen if we completed our circuit with a wire and measured the current with the multimeter at the same ...
Dee's user avatar
  • 21
2 votes
1 answer
46 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 ...
supercat's user avatar
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-1 votes
4 answers
123 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 ...
majduddin's user avatar
1 vote
1 answer
67 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 ...
EE18's user avatar
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2 votes
1 answer
140 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 ...
Fan's user avatar
  • 39
0 votes
2 answers
98 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 (...
Gerard Carrera Cardona's user avatar
1 vote
0 answers
640 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 ...
TeD van Loon's user avatar
1 vote
1 answer
100 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 ...
EE18's user avatar
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1 vote
1 answer
133 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 ...
Subhadip Kar's user avatar
1 vote
2 answers
86 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 ...
Jess's user avatar
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1 vote
2 answers
82 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 ...
Tp86's user avatar
  • 63
1 vote
1 answer
87 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 ...
user50655's user avatar
3 votes
0 answers
179 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 ...
Math Keeps Me Busy's user avatar
0 votes
0 answers
37 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 ...
Lpaulson's user avatar
  • 305
1 vote
3 answers
70 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 ...
David's user avatar
  • 11
1 vote
1 answer
93 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 ...
Math Keeps Me Busy's user avatar
1 vote
1 answer
576 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)$...
Surzilla's user avatar
  • 121
3 votes
3 answers
955 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,...
Mikayla Eckel Cifrese's user avatar
1 vote
2 answers
133 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?
Shubham Singh's user avatar
0 votes
2 answers
165 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?
JePl's user avatar
  • 1
0 votes
1 answer
48 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, ...
Colin Marcus's user avatar
0 votes
0 answers
70 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 ...
komrad2236's user avatar
1 vote
0 answers
60 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 ...
lasb3tas's user avatar
  • 195
8 votes
3 answers
2k 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: ...
Akash Sagar's user avatar
1 vote
1 answer
207 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 ...
axis's user avatar
  • 11
1 vote
1 answer
512 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 ...
puq_87's user avatar
  • 69
3 votes
1 answer
270 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?
L1234's user avatar
  • 47
1 vote
1 answer
388 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 ...
Seidenki's user avatar
3 votes
0 answers
68 views

Why do we use silicon in the crystal direction [1 0 0]?

In MOSFET, we use silicon in crystal direction [1 0 0] , while we use direction [1 1 1] in BJT. What is the reason? I expect the opposite, because we see more atoms on the surface in the direction [1 ...
mohammad rezza's user avatar
5 votes
1 answer
375 views

Why don't we consider drain-bulk voltage instead of source-bulk voltage in body effect?

Why don't we consider drain-bulk voltage instead of source-bulk voltage in body effect? For example, in the threshold voltage formula, we have source-bulk voltage, not drain-bulk voltage.
mohammad rezza's user avatar
1 vote
3 answers
582 views

How does a electrical device draw its rated current?

I am learning electronics and this question has been bugging me quite a bit. If I have a device, let us say rated at 6 volts and 350 mA, this means the device will work when there is a potential ...
Dixshant s's user avatar
3 votes
2 answers
4k views

How do I calculate threshold voltage from the graph?

I have a table of values given to me which contains drain current Id (in μA) and gate voltage (in volts) calculated in the saturation region for a thin film transistor. I need to find the threshold ...
blackblade's user avatar
0 votes
0 answers
108 views

Calculate complex impedance value from voltage in time domain waveform

I have problem. I was doing an electrochemical impedance spectroscopy (EIS) test on my Randles cell. simulate this circuit – Schematic created using CircuitLab The data from potensiostat's ...
Prayander Sahatma Siahaan's user avatar
1 vote
1 answer
158 views

Difference between arsenic and phosphorus in IC fabrication technology

What is the difference between arsenic and phosphorus in IC fabrication technology? When do we prefer one of them over the other?
mohammad rezza's user avatar
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 ...
Polynomial's user avatar
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1 vote
0 answers
501 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 ...
Daniel Stepanoff's user avatar
0 votes
1 answer
130 views

Why is the gamma term missing in the first case of single transistor example?

This is the video. How is the gamma term present in one case and absent in another?
debashish's user avatar
-1 votes
1 answer
284 views

Maximum weight for robot arm - MG996R [closed]

I want to build a robot arm (see here) to move a dumbbell of 2 kg (roughly 2.2 lbs). However, since I have no background in engineering, I have no idea how to calculate / find out if the servos used (...
juliusphysics's user avatar
12 votes
1 answer
942 views

Why does current flow direction matter in welding?

In DC welding, there are two configurations - direct current electrode positive (DCEP) and direct current electrode negative (DCEN). When the electrode is negative, the current flows from electrode to ...
S. Rotos's user avatar
  • 3,217
3 votes
2 answers
554 views

How can I calculate how long it will take equipment in an enclosure to overheat?

This is kind of a follow-up question about determining the heat dissipated from equipment based on power consumption. I have a situation where I have to install a router and UPS system in an enclosed ...
Frank's user avatar
  • 293
0 votes
1 answer
51 views

How to compute flux through a sphere when flux density is given in rectangular co-ordinates?

Compute the total flux of D leaving a sphere of radius 1m, and hence the total charge enclosed by that sphere. D(x,y,z) = xX̂ Attached is my current working and the worked solutions provided to us. ...
Toby Z's user avatar
  • 11
3 votes
2 answers
145 views

Fermi level of metal

Do metals have fermi level? As we know conduction band and valence band are overlaped for a metal. Does it make any sense for metals to have fermi level?
sumita sahu's user avatar

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