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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How do i build a DIY bolometer?

I want to make a device that detects a small temperature variation (less than 1 K) in a diode or a transistor, and calibrate it with a potentiometer, but i don't know how does temperature affect the ...
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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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1answer
65 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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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
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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
54 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
37 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
29 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
49 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
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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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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
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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
105 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
53 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
160 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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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
67 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
150 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
47 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
95 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
30 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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86 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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0answers
81 views

How to calculate neutral base width for an emitter-base junction with forward bias voltage

I am trying to find the neutral base width for an emitter-base junction with a forward bias of 0.75V and a base-collector junction reverse bias of 20V. I am not sure how to factor in the forward bias ...
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3answers
54 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
115 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
70 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
68 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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44 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
156 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
62 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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24 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
139 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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4answers
70 views

Energy Transport in Circuits

I've been reading about how energy is actually transported in circuits (I first read about it here: http://amasci.com/miscon/ener1.html). The description in this article of why electrons don't move ...
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Temperature Effect on Schmitt Trigger Threshold Levels

I have found minimal information on the internet, as well as in multiple data sheets I have looked at. I'm designing for a large temperature range of 150°C. I require a fairly consistent voltage ...
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2answers
81 views

Transformer Secondary Discontinuity

I am using a step up transformer and I am getting a weird discontinuity in the secondary output. Has anyone seen anything like this before? I cant figure out what might cause this. In a one test setup ...
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2answers
49 views

What is impeding current when voltage is stepped up in a transformer? [duplicate]

What is physically impeding electric current when a transformer steps up voltage? Is there some EM field along the conductor impeding electron movement? FYI, I'm not asking about losses or leakage. (...
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2answers
122 views

PN Junction paradox or something else? [duplicate]

[![I am having problem understanding reversed biased pn junction as the explaination provided by my book or any other source about flow of current in forward biased condition seems equally applicable ...
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3answers
241 views

Why should signals in circuits propagate much slower than the speed of light?

I've read a couple of other topics (such as this one and this one) about the lumped circuit abstraction requiring that signal timescales (i.e. the period of the highest frequency signal component) be ...
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1answer
123 views

reverse bias of the gate of an N-channel enhancement mosfet

So how negative can I drive the Vgs of an N-channel Mosfet before damage occurs? Datasheets specify BVDSS and BVGSS but these are "forward" breakdown voltages -- ie the absolute maximum Vds before ...
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1answer
150 views

Can anyone explain reverse bias pn junction using only electrons as charge carriers

In forward bias condition p-type semiconductor is connected to positive side and ntype semiconductor to negetive side and the electrons flow from n-type to p-type to cathode of battery. But imagine ...
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4answers
183 views

What is unit jω?

I have an equation, from which I'm calculating the induced voltage received by an RFID tag antenna. I know that \$ω\$ = angular velocity, but what is \$jω\$? And if \$jω\$ is related to angular ...
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44 views

Are there any general guidelines for knowing which order to find equivalent capacitances/resistances in

When simplifying a circuit with multiple capacitors or resistors is there a generally accepted order for knowing which equivalent capacitors/resistors to find first? Should I start farthest from the ...
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2answers
40 views

Different ways or sensors to detect the weight on an object in a system

I am starting to gather information for a project I am excited about; my project is essentially a barbell that can detect the weight loaded on it. I will quickly summarize the function and restraints. ...
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Physics behind signal reflections and series termination

I have been looking for cause of signal reflections in transmission lines. Everywhere it is concluded that the reason is impedance mismatch. I can understand if the impedance changes in the path of ...
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1answer
50 views

Find electric field due to point charge +Q under given condition

As shown in the image, there are four conditions given: Electric field in figure:1 at point 'P' let = E_P, Electric field in figure:2 at point 'M' let = E_M, Electric field in figure:3 at point 'R' ...
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Error Propagation and Analysis on a experiment due to Voltmeter Constraints

I got a situation: at the moment I am unable to access both channels for Keithley 2182A nanovoltmeter using LabVIEW. However, for some odd reason, while I cannot access the channels at once, LabVIEW ...
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2answers
70 views

How can different voltages produce the same short circuit current?

I hope I’m not just thinking past something trivial but I can’t make sense of this. In this video, https://m.youtube.com/watch?v=XDf2nhfxVzg , variable voltages from .1-20V are used and when he shorts ...

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