# Tagged Questions

The kind of magic without which all of this wouldn't be possible. This tag should be used for questions about the **physics** of the fields that charged particles create and how these fields interact. It should not be used for all questions involving electromagnetism, that would be everything on ...

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### Electromagnet duty cycle

I have a project where I would like to use an electromagnet to lift an item for a longer period of time. I was looking at a magnet like this one: ...
80 views

### What makes a magnetic field probe insensitive to E-fields?

Consider a magnetic field (B-field) probe such as this one: (source) I understand that as as the magnetic flux through the loop formed by the coax shield changes, the charge carriers in the loop ...
2k views

### How to reverse rotation direction of stepper motor

Is it possible to reverse a stepper motor's direction of rotation by changing the polarities of its wires? I'm asking because I have two stepper motors connected to one single driver and mounted on ...
113 views

### Help explaining “reactive power” video: lights do not use any power? [closed]

In the following video the poster wonders whether his lights, which do not seem to consume any power are running on "reactive power": http://www.youtube.com/watch?v=UbKr7aYKSPU Is the poster of the ...
118 views

### Voltage source connected to single inifinitely long wire

I have in my mind a thought experiment which I cannot figure out. Imagine a voltage source working on let's say 1 GHz. One end is connected to a ground, which is very small (we can abstractly assume ...
136 views

### What is the magnetic analog of resistivity?

Would the magnetic analog of resistivity be the inverse of permeability? I ask this because resistivity is defined by E/J, and so taking the magnetic analogs as H/B, I see that this is simply the ...
90 views

### Electromagnet interference with motorcycle

I just got a sport bike which the frame is aluminum the engine is aluminum the swing arm as well. Basically this bike is made up of mainly aluminum and plastics with very little steel or any other ...
371 views

### Does heat affect the magnetic field of an electromagnet?

I know that heat destroys perm magnets, but how about electromagnetics? Does heat affect the strength of an electromagnetic field?
520 views

### Controlling an electromagnet strengh with arduino

This previous question Controlling an electromagnet with Arduino deals with binary control (ON or OFF) only. On my side I need to choose the strength of the magnetic field. It is a home made ...
667 views

### Why does a simple conductor start to emit EM waves when carrying a signal?

I understand that on circuit board traces with a clock, if the higher harmonics have sufficient power, it results in electromagnetic waves being emitted from the traces which creates EMI. What I don't ...
83 views

### Why can't we record amp sounds from line out of amps when we can hear in headphones using line out? [closed]

Suppose there is electric guitar, and we connect it to amplifier (amp). When we connect our headset into line out of the amp, we can hear what we are playing. If so, why can't we record the sound out ...
311 views

### PWM controller to meet EMI/EMC regulations

I'm designing an application in which the current running into a load is controlled by PWM. A microcontroller generates a PWM cycle at 20kHz and this signal is used to control a MOSFET which is ...
141 views

### Does living near a cell tower decrease your overall exposure to RF? [closed]

I understand that my mobile phone will increase its RF levels when it struggles to connect with a cell tower/base station due to distance. Also being nearer a cell tower will increase my exposure to ...
196 views

### How do arcs generate radio-frequency

When I have an electric arc, and put an AM radio nearby, I hear a crackle and the station that I previously heard goes away. I am wondering what is going on with the electricity through the air to ...
335 views

### Are E and B fields in phase in electromagnetic radiation?

I recently wrote this answer, in which I said: Radio waves are electromagnetic radiation. Electromagnetic radiation contains of two components, one electrical and one magnetic. These components ...
406 views

### What is the difference between electromagnetism and electromagnetic radiation?

In a previous question, I asked if having 2 coils of wire with electricity flowing from one to the other is RF, and they replied that it was not Radio Frequency. I was puzzled because I thought this ...
224 views

### Voltage and Current relationship in generation

Please could someone explain why the current is 180 Deg out of phase with the voltage when measured at the generation point and then in phase with the voltage when measured at the load point. I am ...
308 views

### Amperian loop to measure solenoid's magnetic field

My textbook proves the formula $B =\mu_0In$ for a solenoid by taking a rectangular Amperian loop as shown here: The problem I see with this though is that it only takes into account the ...
69 views

### On Electro-galvanic fuel cell [closed]

Hello for every one , my close friend is going to design some of Electro-galvanic fuel cells , and he seeks for more information about it , how does it work ? what are the laws of physics which ...
111 views

### Terminals of three phase power machine

A three phase machine, instead of having six terminals, two for each slip ring, has only four terminals. Because the starting point of all the three coils have a common junction which is usually ...
109 views

### Can someone explain impedance in simplest way? [duplicate]

I know in DC it is Resistance of the load. In AC is it impedance of a line correct? can someone please help me understand impedance and types of impedance. Zero Sequence, Positive sequence and 2 ...
205 views

### On using an electromagnet in a magnetic stirrer

What's the simplest and cheapest way to use one or more electromagnet to to stir a stir bar ? That is, how to control the speed at which the polarities are reversed. I don't want any mechanical part ...
104 views

### Inductive Braking System [closed]

In a traditional braking system, brake pads produce friction with the brake rotor to slow or stop the vehicle. In an inductive Braking System induction is used to extract energy and act as a brake. ...
105 views

### ElectroMagnetic Induction

there is already a electromagnetic brake. I'm thinking to use a electromagnetic induction as brake. is it possible?
389 views

### magnetic field outside solenoid

It is written in our course book that the magnetic field outside a solenoid is negligible and almost zero. Why is it negligible? Is it negligible compared to the field inside solenoid or is it nearly ...
54 views

### How do construct a electrical resistance tomography apparatus

Im interested in constructing an electrical resistive tomography setup to image underground structures. While I somewhat understand the principle, I have found limited information on design and ...
343 views

### Differences between a planar coil and coplanar waveguide to create a local 1D AC magnetic field

Coplanar waveguides (for example picture look here) are often used in research to create a local in-plane magnetic field. Now if compared to a planar microcoil like this, driven by a AC voltage in ...
185 views

### what type of armature i should use in 12v dc magnetic 2 pole motor to get more than 8000Rpm

i m trying to wind a motor but i am new at this so can any one can tell me how can i wind an armature to get more than 8000 Rpm in a 2 pole magnetic motor of 12 volts
610 views

### Suggestion to electrically disable a Faraday Cage

My plan is to ultimately develop an Autonomous Faraday Cage. The project seems very straight forward; however, I am unsure on how to effectively control the cage (turn on and off). I have constructed ...
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### Electrical Displacement Transducers

Please can you clarify for me what responsivity, maximum range and linear range mean in relation to an electrical displacement transducer? edit: I know now that responsivity is just output/input ...
166 views

### Electrical circuit / transformer in series?

I would like to pull out 5v 3A max in series from an already existing connection from the mains 240v 40A connection. Current circuit: What I would like to implement: What are the possible ...
105 views

### Pros and Cons of 3 Different Transducers

What are the pros and cons of using these different transducers? I can't find see what the difference would be between either of them? I mean, they are all used in converting energy right? Linear ...
779 views

### In a DC motor, is there one commutation point that is optimal in all respects?

This recent question got me thinking about commutation timing, and why advancing it can be desirable. However, I wanted to consider more deeply the underlying phenomena, and I'm pretty sure my ...
169 views

### Kill with voltage [closed]

Is it possible to get so much volt in you, that you become capable of killing another human being Example: the game ''infamous''. In the game, you are literally living on volts. So my question is ...
718 views

### Is it valid to consider back-EMF in a DC motor equivalent to increased inductance?

I know that back-EMF can be considered as a voltage source in series with the motor which is proportional to speed. This is the common understanding, and I totally get it. Before I understood this, I ...
357 views

### Dirty electricity filters how do they work?

There are videos on youtube about finding sources of high EMR. In this videos they reduce EMR level by plugging some 'dirty electricity filters' in wall outlets. I ...
242 views

### Calculating what frequencies a dielectric can be considered perfect

I have a problem that is likely going to be on my E&M final this semester that my classmates and I can not figure out how to solve. The question is At what frequencies can Earth be considered ...
172 views

### Electrical Generator Windings - Is there an “ideal” way to wind?

I've got a question that's been bugging me for a while. Is there a "best" way to position a magnet and wire coil inside a generator? I saw a "how-to" on how to build a wind power plant and they had ...
697 views

### Open Source or free electric field mapping software

Looking for recommendations for 2D (or 3D) electric field mapping software. I want to be able to populate a series of electrodes in a plane and understand the equipotentials present when these ...
75 views

### How can I find the stored energy in a 2d triangle that has a different electric potential at each point?

I am writing a FEM solver for a project. I need to calculate the total energy stored in my mesh so that I can compute the capacitance of the solution. So obviously I have to loop through all the ...
226 views

### emi standards/best practices for PC cases

According to an EE friend, the FCC specifies EMI tolerances (max outputs) for PC components, including cases. However, here it says that there are standards for a number of components but not cases. ...
98 views

### What characteristics of magentic coil is the most important for VLF sensitivity

I try to sense a VLF magnetic field (1-100Hz) by using a coil. The field is very weak and in most of reading there is too much noise. Is there the most important characteristic of the coil, should I ...
881 views

### How to convert a three wire hall effect sensor to a 2 wire sensor?

Would there be any possibility to convert a three-wire hallsensor to a 2-wire equivalent. The connections are a V+, GDD and OUT. The voltage between V+ & GDD would be 24V and the OUT port would ...
226 views

### Faraday Cage - Detecting one

I am looking for a cheap and easy way of creating a small electronic device that is capable of detecting whether or not it is inside a Farraday Cage. Hopefully, without an external sensor/emittor.
267 views

### M.S. Math to Engineering Ph.D : Mathematics in Electrical Engineering

I have two Bachelor's degrees. One is electrical engineering and the other one is mathematics. I am studying mathematics (partial differential equations) in the graduate school (Master course) now. ...
477 views

### How to determine the force of a solenoid based on inductance

I'm looking to potentially build my own small solenoids, I thought perhaps that I could take an Air core inductor, a spring, piece of plastic, and conductive core and build my own. Is there a way to ...
394 views

### Multi-tap transformer current handling capability

I have a transformer with a single secondary winding but with multiple taps, as shown in the image. It is rated at 4A @ 24V (96VA). Does this mean that at lower voltages (16V and 8V) it will be able ...
128 views

### Automobile ignition coil (spark coil)

Question: How is this possible to get 1:1000 electric potential scale while primary/secondary loop scale is only about 1:100?