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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GaN Vs IGBT performances

I was making some research on GaN and I do not understand why GaN is so reveolutionnary. When I take a look on the following specification RdsOn and Coss (Cds + Cgd), the GaN semiconductor has lower ...
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Calculation of series circuit elements

I have a series circuit. Should it be true for this series circuit if I true to write like: ...
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-2 votes
1 answer
53 views

Using an air pump for an pneumatic forearm trainer [closed]

I am attempting to create a forearm training device which looks like this (I don't know what it's called). Can I use this air pump motor with an arduino? It can provide pressure up to 100 kpa, but I ...
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9 votes
3 answers
1k views

Is charging a capacitor to a new DC voltage fundamentally lossy?

There has recently been a question about switching losses and Landauer's principle entered the discussion. I included it in my answer because I believe, a capacitor fundamentally cannot be charged ...
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Does coil winding impact current direction? (Lenz Law)

When a magnet is moving toward a wire loop north-side first, the current goes counterclockwise according to the magnet's perspective, as shown in the image below from Wikipedia. Now, consider a ...
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2 votes
1 answer
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Difficulties in modelling magnetic levitation system?

I am currently working on and writing a project (not homework) surrounding magnetic levitation with an electromagnet having to levitate an object underneath itself. I have taken a look at relevant ...
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What is the explanation for a haptic effect when tracing one's finger along a powered device's chassis? [duplicate]

I have a mid-2012 Macbook Pro Retina, and over the years I notice that when I wipe my finger along the surface of the chassis (like when wiping off dust), I sometimes feel a vibrating effect, a more ...
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1 answer
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Why does short band (high frequency) radio travel longer than low frequency?

In physics, we are taught that longer wavelength (lower frequency) have a lower attenuation in air, and thus is able to travel longer distances. However, when talking about radio channels, short wave (...
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MOSFET gate substrate voltage

In a MOSFET the channel is formed between gate and the body it would sense to use gate body voltage to form the channel. Why is gate source voltage used to form the channel?
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3 answers
106 views

Signal Integrity in electronic systems

When I went through EMC testing of some electronic boards, I observed that the frequencies of the EM waves generated by the boards are at the fundamental frequency with multiples of some whole number. ...
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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: \$ \...
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1 answer
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Experiencing issues with VHDL Code ModelSim: Wave Generation

I'm working on this project where I'm basically supposed to generate square wave (and other types of wave) using VHDL. The time period can be adjusted to either increase or decrease its frequency, and ...
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What is the EMF induced between two points in a closed wire loop?

Farday's law says if I change the magnetic flux through a closed loop an emf would appear. Between what two points is the EMF calculated? Let's say that my calculations give me an E=−dΦdt=10V. What ...
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7 votes
1 answer
446 views

5G and Radar Altimeter Interference - Am I Taking Crazy Pills?

I can't understand where the math supports the concept of 5G frequencies interfering with aircraft altimeters. Can anyone point out the holes in my logic or educate me? Knowns: Aircraft altimeter ...
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2 answers
74 views

What is the minimum capacitance Cx on LM555

I want to measure a capacitance between 10pF and 500pF and feed that information to a microcontroller. I was wondering if a CMOS LMC555 configured in astable operation could do the job with the ...
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Combining sinusoidal waveforms

Please can someone assist me with how to work this out? I know the answers as this is a practice question, but not sure how to get there. Two AC waveforms are described by the expressions: V1 = 190 ...
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What type of polarization does this wave have?

I just took a test today and one of the questions asked was to classify the polarization of a wave. The wave consisted of x/y components $$E = 3\cos(wt-kz) x + 4 \cos(wt-kz) y$$ I classified this as ...
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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 ...
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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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-1 votes
1 answer
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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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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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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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1 vote
2 answers
93 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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0 votes
4 answers
334 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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1 vote
1 answer
68 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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3 votes
2 answers
218 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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2 answers
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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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5 votes
5 answers
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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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2 votes
1 answer
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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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-8 votes
4 answers
335 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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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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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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2 answers
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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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2 votes
1 answer
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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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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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0 votes
1 answer
82 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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0 votes
3 answers
153 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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5 votes
2 answers
398 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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-1 votes
1 answer
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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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0 votes
1 answer
65 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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0 votes
1 answer
35 views

Electrical work sign convention

If I understood the correct sign convention it's as shown in the below sketch
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1 answer
269 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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0 votes
2 answers
53 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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0 votes
4 answers
409 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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1 vote
1 answer
360 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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0 votes
2 answers
62 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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2 votes
2 answers
220 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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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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6 votes
5 answers
1k views

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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0 votes
2 answers
123 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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