Questions tagged [physics]
Physics is the natural science that involves the study of matter and its motion through space and time.
301
questions
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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
111 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
34 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
57 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
28 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!
2
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0answers
84 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
27 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
52 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
112 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
69 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
54 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
41 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
59 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
4k views
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 ...
1
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2answers
95 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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0answers
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
127 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
63 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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0answers
25 views
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 ...
1
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2answers
68 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 ...
0
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0answers
17 views
How do i set up an offset antenna?
How do i set up an offset antenna? I have two offset antennas. 1 for receiving and the other one for transmitting, they are at the same altitude. I don't know how to set up the angle because the beam ...
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2answers
44 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
97 views
PN Junction paradox or something else? [duplicate]
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3answers
214 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 ...
2
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1answer
62 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 ...
0
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1answer
127 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 ...
2
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4answers
172 views
What is unit jĻ?
I have an equation, from which I'm calculating the induced voltage received by an RFID tag antenna. I know that \$Ļ\$ = angular velocity, but what is \$jĻ\$?
And if \$jĻ\$ is related to angular ...
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0answers
43 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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0answers
78 views
How to simulate a MMF fiber in COMSOL Multiphysics?
I am a complete newbie to COMSOL multiphysics, but I have to study and simulate the effects of temperature on multimode optical fibers (MMF) using COMSOL multiphysics for my Bachelor's thesis.
I know ...
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2answers
39 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. ...
16
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5answers
2k views
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
47 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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0answers
21 views
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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0answers
41 views
Transformer operating frequency clarification
I'm trying to design a small audio transformer.
Specs are as follows:
...
0
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2answers
66 views
How can different voltages produce the same short circuit current?
I hope Iām not just thinking past something trivial but I canāt 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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1answer
74 views
voltage potential energy clearance?
1 coulomb = charge of 6241509074460762607.776 protons(fixed amount of energy passing thru certain point).
So 1 volt = 1 joule(energy) per 1 coulomb.
and 2 volts = 2 joule(energy) per 1 coulomb.
does ...
0
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1answer
59 views
Bidirectional level translator using N channel MOSFET
I'm using a n channel MOSFETa bidirectional level translator. The case when the body diode conducts the source end will be literally 0V or forward voltage of body diode, so the difference in voltage ...
0
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1answer
92 views
Is it logically explainable that current is lower when torque higher?
I am modelling a motor with a little simulation script. The principle is:
Input is the traction force needed to be provided by the motor
Output is the current to be provided to the coil of the motor (...
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0answers
39 views
Schottky diodes operation
As far as I know the depletion region is created due to the diffusion of majority charge carriers which expose the charge of their ions.
Is this the same for Schottky diodes (electrons diffuse from ...
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2answers
143 views
How does the arc extinguisher work in a miniature circuit breaker?
In a miniature circuit breaker, as shown below, the distance between open contacts is much less than the distance between metal bars in the arc extinguisher part (the gap gets progressively longer ...
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0answers
54 views
Magnetic locks with paramagnetic materials
Well I was wondering why magnetic locks are made of an electromagnet and a ferromagnetic material and not an electromagnet and a paramagnetic material.
The magnetic attraction between the ...
2
votes
5answers
93 views
Why is Frequency Conversion Additive in Acoustics Beating, but Multiplicative in Heterodyning?
In radio electronics, one of the first concept to learn is frequency conversion by using a mixer. And it's strongly emphasized that the mixer is a multiplier, not an adder used in audio circuitry. The ...
0
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1answer
71 views
Magnetic force and Coulomb force
Lets have 2 electrons travelling with some speed relative to a static observer.
The force between those 2 electrons will be the Coulomb force and the magnetic force.
Is it forbidden from the laws of ...
2
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1answer
54 views
Mechanical Circuit Analog Question
I'm doing a practice problem from https://6002.catsoop.org/F19/ex11/mechanical_analog
The problem is as follows: A mass m = 10 kg is at rest on a horizontal plane with viscous friction coefficient B =...
2
votes
2answers
61 views
Magnetic force as a function of PWM frequency
Consider an experiement with a DC source feeding an coil with a constant DC current I. The coil with an iron core attracts a magnetic plate with mass m with force F. The force F is higher than Fm and ...
0
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1answer
650 views
Slayer exciter(Mini Tesla Coil) Not Working[IRFZ44N]
I made a tesla coil as https://www.youtube.com/watch?v=Ca2e3evwVK0 's circuit. the MOSFET seems to be getting hot and current passes through the primary but I get no response from the secondary.
...
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2answers
85 views
How to find the voltage of a capacitor in a Op-amp + RC network?
I found this practice problem online which asked to find the voltage across the capacitor as a function of time. The circuit is:
My intended approach is to first find the initial condition when the ...
1
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1answer
118 views
Deep explanation on TVS diode voltage suppression?
I am looking for a deep explanation on why a TVS diode suppresses voltage. All of the research I have done on Google just says 'it suppresses voltage by shunting current', but this doesn't make sense ...
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1answer
52 views
Network Identification - How to find R1 and R2
I've been working on this practice problem I found online.
So, from the graph I understand that \$R_{eq} = 2000\$ for the entire circuit. Since I want to find \$R_1\$ and \$R_2\$. To do this, I turn ...
