Questions tagged [field]
The field tag has no usage guidance.
69
questions
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3answers
59 views
If greater potential energy is toward pos charge, then why PN energy band diagram show lower energy toward pos charge across depletion region?
If in an electric field, greater potential energy and voltage are toward the positive charge and away from negative charge, then why do PN energy band diagrams indicate lower energies toward the ...
10
votes
4answers
817 views
Construction for a homogeneous field using permanent magnets
Please let me describe what I am trying to achieve and I will pose my question in the end.
I am trying to design a small chamber which can have a uniform magnetic field inside. I want to see if a ...
2
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2answers
95 views
What causes the electric field to change over series resistors?
So for example if we have a a wider and a narrower wire of the same length in series, since v1A1=v2A2, in the narrower wire the charges will move with a greater velocity. Since v is proportional to ...
-1
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2answers
70 views
Relation of drift velocity and electric field?
So I attached the standard derivation of the relationship between drift velocity and electric field.
My problem is:
Tau=s/Vd, where s is the mean free path of the electron. Substituting this into the ...
7
votes
1answer
712 views
Sewing machine motor repair
I'm a sewing machine mechanic, trying to increase my electric motor knowledge.
I have a Bernina 830 sewing motor where the carbon brushes ran down and the wire damaged the commutator and ran a groove ...
1
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0answers
38 views
Field Coil Help - Varnish, cotton, wrapping etc
I am restoring a 1940s sewing machine. The motor wire war in really bad condition and needed replaying. I take off the wrapping on the coils to solder some new wire. The wrapping that was used was ...
0
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1answer
39 views
How to detect a magnetic field from a distance?
I want to detect a magnetic field, like those of small neodymium magnets, from at least 6 inches away (the further the better, I'd like at least a foot but I won't ask for too much). I'd like to do ...
0
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2answers
62 views
A very basic question about PLC field input switches
Below shows two simple ladder logic examples written for a PLC:
As far as I understand, the -| |- and -|/|- above are the symbols we write for the PLC not the actual input switches.
But we also need ...
-1
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1answer
40 views
Transistor Electric field [closed]
For unbiased transistor, is the maximum electric field larger in the emitter ā base junction or in the base ā collector junction? Why (draw)
0
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0answers
40 views
What are the chain reaction that create the electromagnetic wave?
From my very limited knowledge I know that an electromagnetic wave is created by some chain reaction of accelarating/oscillating electric and magnetic waves, I also know about how the electromagnetic ...
0
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2answers
68 views
Why is \$E_1=\frac{F}{q}=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_2}\$, instead of \$=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_1}\$?
I have a question about these electric field strength formulas
Why is \$E_1=\frac{F}{q}=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_2}\$, instead of \$=\frac{K\frac{Q_1 Q_2}{x^2}}{Q_1}\$?
\$K\$ is constant \$=9 \...
2
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1answer
109 views
Does this sensor measure electrical or magnetic fields (with oscilloscope)
I want to measure electrical and magnetic fields of the frequency 50Hz to 1MHz with my oscilloscope.
For electrical fields I learned that any bunch of metal will work.
For magnetic field derivation ...
0
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2answers
50 views
Magnetic field of a coil composed of stacked coils
Basically my question is that if you have a coil with N turns with its ends connected to a source of current (I), and you have another coil which is N number of single coils stacked on each other with ...
1
vote
0answers
29 views
Parabolic wave equation, electric and magnetic field definitions
The split step solution for Parabolic Wave Equation (PWE) applied to the tropospheric propagation problem is:
$$u(x+\Delta x, z)=e^{ikM(z)10^{-6}\Delta x}\mathfrak{F}^{-1}[e^{\frac{-ip^2\Delta x}{2k}}...
0
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0answers
25 views
Electric Field in a Multi - Cell Cavity
let's consider a multi cell cavity like this one. The image has been taken from here.
My question is about the magnitude of the electric field inside it. Let's consider each single cell of this ...
1
vote
1answer
159 views
Interface conditions and surface current density
let's consider the interface condition for magnetic field strength:
1) I do not have a clear idea of what js represents. If I have understood it correctly, it is a linear density ([A/m]) of a surface ...
0
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2answers
51 views
Floating Conductor Next to AC Power Source
Let's say I have a conductive metal sphere connected to a 50Hz 1kVrms AC Power Source referenced to Earth ground. About 3cm away, there's an identical metal sphere suspended by a non-conductive ...
0
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1answer
97 views
Does a pcb as patch antenna isolate itself?
I'm currently working on a prototype patch antenna for UHF. Since I'm out of copper at the moment, I used empty PCB's as base material (don't mind the PCB in between, it's only a spacer):
So now my ...
1
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1answer
72 views
Magnetic Monopoles and Magnetic Current Densities
I see that in electronic engineering the Maxwell equations are written with also some terms which represent the magnetic charge and the magnetic current densities. I was told they are inserted only to ...
0
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0answers
73 views
Alternator field winding VS equivalent inductor
I have a question which I know is going to be more opinion biased than factual. I know this isn't the purpose of the forum, but I would really appreciate some extra opinions so I'm going to ask it ...
1
vote
0answers
51 views
Should I daisy chain start connect or wire separately?
This is related to field wiring schemes and interference. Sometimes tens of transducers are needed to be coupled to a single-ended data acquisition board's analog input channels where the transducers ...
3
votes
1answer
155 views
Detrimental impact of magnetic field on PCB and battery?
We are developing a small consumer electronics product consisting of a small 4-layer PCB along with a few PDM microphones and BLE chip/ an antenna, as well as a LiPo battery. We are locating a small ...
-1
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3answers
2k views
What is the SI unit of magnetic force?
As derived from F = qvB sinĪø, what is the unit of magnetic force, and why?
Edit: I mistakenly asked about magnetic field before. -- I'm asking the magnetic force.
1
vote
1answer
126 views
Understanding oscilloscope pattern
This is likely an obvious question for anyone with professional experience but I'm just a humble software engineer trying to fathom the mysteries of my oscilloscope...
I created a simple square wave ...
1
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1answer
34 views
What determines the direction and cause of electric field exerted on test charges?
-I understand when there is an on-going electric field, if it is produced by a positive charge, the direction of electric field is away from it etc. And, if we get a +ve test charge, it repels it, and ...
1
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1answer
77 views
use battery to generate weak electric field?
i am a biology student interested in how marine animals react to weak electric fields. My professor and I want to do a trial experiment and were hoping to rig something up ourselves for cheap. Is ...
0
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1answer
99 views
Enhancement type MOSFET - channel formation
In an enhancement type MOSFET (an n channel one assumed here), when a positive gate to source voltage is applied, the holes of the substrate near the gate move deeper into the substrate away from the ...
0
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1answer
288 views
Question on MOSFET - small signal model
In the small signal model of a MOSFET, the current from the drain to the source (for an n channel MOSFET) is a function of the gate to source voltage only.
But, if a positive voltage was not applied ...
2
votes
1answer
138 views
How to extract energy from an alternating electric field?
Given an alternating electric field E inside e.g. a big parallel plates capacitor, how can you make use of the field's energy to power an electronic device?
So far I thought of putting two smaller ...
0
votes
1answer
50 views
E fields and M fields in Near Field
I am reading a textbook that mentions that small loops with high dI/dt on a PCB tend to produce predominantly magnetic waves and stubs with high dV/dt tend to produce predominantly electric waves in ...
0
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0answers
58 views
What is the direction of electric field inside a battery?
Outside the battery, in the conductor it is in the direction of conventional current. But what about inside?
Somehow linked: For p-n junction, at the depletion region which side is at higher ...
1
vote
3answers
565 views
Solenoid's field intensity calculation dependency on width/diameter of coil?
Textbook formula for field intensity in solenoid coil is
H = (N * I) / l
H magnetic field intensity in ampere-turns
NI ampere-turns
l is length between the ...
0
votes
1answer
94 views
How to excite a fluorescent lamp without connecting it?
I'm a newbie in electrical engineering, so this might be a silly question. But are there any standard ways to create an electric field over a volume of air, strong enough to excite a compact ...
3
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5answers
8k views
How does a capacitor resist changes in voltage?
I was reading about how capacitors work and two sentences confused me:
"A capacitorās ability to store energy as a function of voltage (potential difference between the two leads) results in a ...
0
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1answer
61 views
Strong H fields: electronic items susceptible to thier damaging effects and how to shield them
This is another question related to magnetic fields. I'm trying to determine the thickness of copper foil that would be required to shield common electronic items from H fields of about 133 A/m over ...
0
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4answers
343 views
What is voltage exactly? [duplicate]
First, let me start off by saying that I have read the answers to this question (which is the same as mine), but the answers basically explain the different ways voltage is created or compare it to ...
0
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0answers
31 views
Electrical field of cathode ray
In my study book of radio frequency engineering is a question, which is pretty odd in my opinion.
Calculate the electrical field of a cathode ray for the cases r < d and r > d. There are two ...
0
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3answers
3k views
How does the range of bluetooth increases by adding an antenna?
I have seen too many tutorials on how to increase HC-06 bluetooth module range. They all involve cutting the on-board antenna and adding an external one (a piece of wire or a 2.4GHz antenna). I was ...
1
vote
3answers
1k views
Disposable camera EMP coil not producing any field
I recently took on this project: https://www.youtube.com/watch?v=WIMhraVcdTg
Trying to use a disposable camera as an EMP generator.
I wrapped my wire around a bottle, but it still won't do anything,...
1
vote
2answers
95 views
Electric Field electrical charge
Hey i dont know how to solve this. Can somebody help me?
In the two-plate arrangement shown in the sketch, there is homogeneous electrical field strength
$$\vec{E_0} = -\vec{e}_y * 10\frac{kV}{cm}$$
...
1
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1answer
141 views
Is Work done to Transfer Energy?
The example below is for a perfect lossless circuit with no resistance for the sake of illustration only. In reality this does not exist, but again the purpose is for simplicity.
If there is 1 Joule ...
0
votes
1answer
76 views
Does my electric clearing field actually make ions?
I am using an electric clearing field of 15v/10cm (~150V/m) to remove ions from a test chamber, however I'm wondering to what extent the localisation of the field's reference voltage plays a role.
...
0
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2answers
283 views
EMI Field Strength
I tried to look up this kind of question in the archives but didnt find much usefull information. I also have another question in regards to EMI but I will ask this later in a seperate post.
...
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0answers
137 views
Equipment to measure strong constant (in time) and slowly changing electric fields
I would like to measure the electric field in the vicinity of an object of interest. I would like to have decent spatial resolution (i.e. be able to pinpoint a measurement to a point in space within ...
1
vote
2answers
184 views
How does current flow inside a grounded coax shield?
I have been trying to reconcile the fact that current flows on the inside of a coax shield with the common practice of grounding the shield. These ideas seem contradictory at the moment.
For a 2-wire ...
2
votes
3answers
264 views
Help me understand electrical fields better
I have a hypothetical scenario that would help me better understand (I hope) electrical fields and propagation of electrical fields better.
So let's have a super simple circuit with one voltage ...
-1
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2answers
84 views
Would the Electric Fields of simultaneously transmitted waves affect eachther
If there are 2 waves, with different frequencies, wouldn't the Electric fields add up and impact both waves regardless of the frequency difference?
I attached a picture of what I mean, when there are ...
0
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1answer
64 views
Find error in mathematical proof of electromagnetic fields
This is wrong but I can't figure out what is wrong, could someone help me find the errors.
2
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1answer
159 views
Antenna design for radio energy emission into a fresh-water test tank
I would like to emit as much RF energy in the frequency range of 433.9 to 434.5 MHz into surrounding fresh water with a 100mW transceiver.
The antenna is in the middle of a 4mx8mx2m fresh-water tank ...
1
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2answers
2k views
Does a simple bug detector detect electric field or magnetic field?
Hi.
This is a very cheap and simple bug detector that is supposed to make sound
when it detect RF signals between 100Mhz-2600Mhz.
I found out that it doesn't do what it supposed to do,since its
...
