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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58 views

What is this linear encoder from a old inkjet printer using a thin metal rod and a metallized glass plate?

What is the working principle of this sensor ? It was found in a canon inkjet printer from around 2000-2005. Not a fancy model, though. The metal rod broke, as it is surprisingly fragile. It doesn't ...
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Why we still observe leakage at drain when we ground source. gate, and body of NMOS? [duplicate]

Why do we still observe leakage at the drain when we ground the source, gate, and body of NMOS? I think it has something to do with the p well implant or doping concentration but I'm not sure
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Why we still observe leakage at gate when we ground source. drain, and body of NMOS?

Why we still observe leakage at gate when we ground source. drain, and body of NMOS? I think it has something to do with the gate oxide or capacitors but im not sure
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34 views

Measure capacitance of planar electrodes for sensing gas using Arduino/Nucleo board

I am looking to do post-grad research study next year in the sensory field for sensing gases like hydrogen, nitrogen or ammonia (not decided yet). So trying to understand what is out there and how ...
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1answer
36 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?
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87 views

Suppose there is a standing wave in a transmission line at high power. Will the nodes of a wave 1 ft apart be hotter than the antinodes?

I was looking around for an evening and could not find an answer. I am also fuzzy on the exact electromagnetic physics principle of why a reflection occurs (please do not say "because the ...
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4answers
127 views

BJT Early effect and the small signal model

As the collector-emitter voltage changes, collector current changes due to the Early effect so the base current must also change. In the small signal model, we only account for the change of collector ...
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1answer
51 views

Physics of BJT and charge profiles

Why does a linear charge profile in the base imply no recombination of charges at the base, but in case exponential decay it implies recombination at the base? Why does charge density at the base ...
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2answers
175 views

What causes energy to be radiated away from an antenna

This seems like such a simple question but there is just something that is not making sense to me. I'm a 4th year ECE student so I think I should know this answer. Here's the question: Recently I've ...
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2answers
55 views

Reactive power and eletro-mechanical analogy

Regarding this question, I will try to use the analogy of the differential equations $$F = m\frac{dv}{dt}$$ and $$V = L\frac{dI}{dt}$$ and $$w = \int Fv dt$$ with $$w = \int VI dt$$ to figure out the ...
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5answers
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Color LEDs and voltage: why the discontinuity on blue?

Something is bothering me when I consider the forward voltage of tiny monochrome LEDs. Consider the following data from datasheets of tiny SMT monochrome LEDs of different colors (sources red yellow ...
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1answer
91 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 ...
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282 views

Analog Is Digital? [closed]

As I started reading a bit about analog vs digital signals, I keep returning to this thought. This could be something pretty obvious to the pros out there, but is it safe to assume that underneath it ...
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0answers
42 views

Solutions to wave equations

In the following steps for a solution to the Telegrapher's equations, I don't understand how equation 9.17 follows from 9.16. Substituting in \$\gamma\$ as given, it seems that the result should be \$...
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4answers
237 views

GaN Vs SiC physic properties

Here is a table which shows the différence between GaN and SiC: I have no knowledge about physics of components. I have just some bases. In the above table I do not see real difference between SiC ...
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2answers
106 views

Holes in RF shield, what frequencies can escape?

So this is part of a theoretical design problem that I've come across not too long ago, and still can't find a satisfactory answer for it. Assume a large (infinite) metal plane with a round hole in it ...
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1answer
89 views

Trouble to understand Johnson Nyquist noise: why I don't find the "4" in the voltage fluctuation

I am a little bit confused to precisely understand the meaning of the formula: \$\langle \overline{V}^2 \rangle=4 k_b T R \Delta f\$ Imagine a resistor \$R\$ in \$x=0\$ thermalized at temperature \$T ...
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42 views

Do you get correct graph of transfer characteristics(CNTFET), if you take +ive Vds(constant) value instead of -ive. As mostly CNTFETs are p chnl FETs

I'm studying transfer characteristic curve of CNTFET to get value for mobility, S.S, etc. According to my basic background knowledge, NMOS curves lie in the 1st quadrant. While for PMOS they lie in ...
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1answer
73 views

In semiconductor physics, how can we know which units to use for Boltzmann's constant?

I'm working through Example 3.9 from Sima Dimitrijev's Principles of Semiconductor Devices textbook, and I'm not sure how to know which units to use for k in solving for \$v_{th}\$ in part a. The ...
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3answers
113 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 ...
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2answers
130 views

Depletion Region Capacitance in MOSFET

Hi, I would like to ask about the behavior of a MOSFET as a capacitor, particularly at the onset of inversion/weak inversion - see Fig 2.6(c) At this stage in Fig 2.6(c), there is positive charge at ...
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1answer
56 views

Relating Temperature and Battery Performance (HELP)

I am a grade 11 student performing a experiment on relating how external temperature affects the performance of a battery, so its voltage and current change. I've done so much research and cant find a ...
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1answer
44 views

Inductor/Electromagnet used to lift up a magnet? Joules to Newtons or Joules to Gauss?

With interest in using an electromagnet to lift up a magnet. I dove in. I will state general information. The set up is unknown but I'm interested in the physics/electrical engineering involved in ...
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1answer
33 views

Electrical work sign convention

If I understood the correct sign convention it's as shown in the below sketch
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1answer
143 views

Voltage and current tolerances

I'm attempting to self-learn as much as I can about electrical fundamentals and circuit building (red flag here I'm sure, but want to be completely honest in the hopes that someone can offer some ...
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2answers
52 views

Can we use the sawstop concept for metallic doors as well for home? If not how can we protect from door finger injuries? [closed]

Is it possible to apply the Sawstop concept where the system induces small current and monitors changes when human finger is inserted? If not what are the nest ways [for metallic doors that closes ...
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37 views

Any recommendations for gas discharge tube mathematical modeling references?

Any recommendations for gas discharge tube mathematical modeling references? Lieberman and Lichtenberg (2005) Principles of Plasma Discharges and Materials Processing (see @AdilMalik 2020-12-21 ...
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4answers
215 views

What happens to the generator if we don't consume the generated electricity from generator? Only theoretical explanations, please

As all we know, there are different ways of generating electricity such as solar cells, wind turbines, dams, etc... I'm gonna pick wind turbines as a metaphor to tell what is on my mind. Let the wind ...
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1answer
190 views

How does a single phase shared neutral circuit actually work, physically?

Okay so this is a two part question. First Question is probably more of an ELI5 question. But I am a fairly experienced electrician (NOT AN ENGINEER mind you.) but I have a generally good working ...
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2answers
56 views

How do I set up a circuit in order to help me measure the resistance of a 1-meter length copper wire with changes in temperature?

I am a high school student and I am taking Physics at school. I have been given the task of measuring the resistance of a copper wire with changes in temperature, however, I have no prior knowledge of ...
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2answers
178 views

What causes flicker or 1/f noise?

What physical processes causes the generation of electrical and radio/EM/RF flicker or 1/f noise? Or why are those sources not generating normally distributed electrical observables (such as thermal ...
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58 views

How do I effectively trip a digital Hall effect sensor with low current. Magnetic field amplification?

This is part of a more complex project for school but here is what you need to know to help me. I have a DC voltage from 0-5 volts I must include a resistive load. The Hall effect sensor trips a ...
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5answers
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Does "a signal is buried in noise" mean that the noise amplitude is still smaller than the signal amplitude? (Special case: Lock-in amplification)

I heard that Lock-in amplifiers (LIAs) especially play to their strengths when the signals are weak compared to the noise level. But then I talked with someone about it, who understands the principles ...
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2answers
92 views

What happens after disconnecting DC powered inductor?

Voltage over an inductor is proportional to the di/dt. I want to know what happens if I disconnect an inductor from a DC power suddenly. After disconnecting no current could pass through it, right? So ...
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3answers
198 views

How can a crossed dipole (turnstile) antenna be omnidirectional in 3D?

A crossed dipole or Turnstile antenna is said to not only be omnidirectional in the plane of the two dipoles, but its pattern is roughly spherical, there's no null along the axial (boresight) ...
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1answer
67 views

Crosstalk between transmission lines

I was reading these slides about crosstalk between transmission lines. At page 6 there is this circuital model to describe the effect of mutual coupling between these two lines: My doubt is: why \$I_{...
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1answer
132 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 ...
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1answer
34 views

Confusion on Voltage levels in Digital Waveforms

My question is why Io is in different direction when Vo=H and Vo=L respectively? I really can not understand the underlying mechanism!
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0answers
88 views

What is the noise electrical appliances / lights make before the power goes out during a blackout? [closed]

I have no prior EE experience, but I am curious about why there is a strange noise when a blackout occurs. It makes a high pitched noise right before the lights fade out? What causes incandescent ...
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3answers
56 views

How does being exposed to strong radiations effect nanosatellite electronics equipment?

I'm on paper designing a nanosatellite power system. The satellite would be orbiting in LEO. And I am wondering how and what type of radiation would affect its electronics. The system has a ...
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2answers
119 views

Where does Ohm's Law, Kirchhoff circuit laws, etc, come from? [closed]

I know that these various laws that we use are often commonly accepted in practice but I am always curious how far down the rabbit hole you can do until you hit something that you just accept as true. ...
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1answer
71 views

Power calculation

Let's say I'm gonna charge a 1mF capacitor from 0 to 100V in 10 seconds. Assuming there's no limiting resistor nor any other losses, the total energy that must be tranfered from the 100VDC supply to ...
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1answer
83 views

Semiconductor diffusion current over time

Suppose you have an injection of holes into a semiconductor such that at some time you have this linear hole profile: Because the diffusion current at any point is proportional to the slope of P at ...
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0answers
49 views

Since current through capacitor (between the plates) is displacement current, what is the current flowing to the leads of a capacitor called?

Since there is no conduction current through the capacitor, what is the current that flows between the battery and the leads of the capacitor while the plates are charging (or discharging) to their ...
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2answers
60 views

How does writing a bit to a GPIO pin turn on my induction motor?

I have a Raspberry Pi 3 hooked up to a Yahboom 4wd robot controller board: When I set GPIO PIN 2 to output mode, then write a 1 to it, the fan turns on. What actually happens, physically, that turns ...
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9answers
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Why doesn't higher frequency mean higher data rate?

My question is very primitive :) I've read multiple articles today and answers here, on Stack Exchange, but still don't understand one thing. Why doesn't frequency itself affect data rate in mobile ...
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2answers
302 views

How to automatically reverse the direction of a motor without human intervention?

I am working on this project where I have an arm at rest want a brushless DC motor (BLDC) to automatically reverse: (I've added an image and text above for a visual reference) Given that I am taking ...
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1answer
65 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 ...
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25 views

Side lobe level of an aperture antenna

There is a electric field in the far zone of the rectangular aperture antenna as shown below. Antenna lies along the xy plane. $$E_{\theta}=\dfrac{jke^{-jkr}}{4\pi r}\dfrac{sin(0.5\lambda k sin\theta ...
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2answers
156 views

My oscilloscope tells me I vibrate at 60Hz. How?

As I live in North America, my initial hypothesis is that I'm picking the 60Hz from my house's power line. But, to my understanding, my body can't be a 60Hz antenna (1/4 wave antenna length for 60Hz ...

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