The engineering discipline concerned with the study, design and application of equipment, devices and systems which use electricity, electronics, and electromagnetism.
Questions tagged [electrical-engineering]
634 questions
72
votes
9 answers
Why do fans spin backwards slightly after they (should) stop?
Today, I've decided to observe my PC fan as I shut the computer down. The fan slowly lost angular momentum over time. What I've found really interesting is the fact that the momentum vector change did not stop at the zero vector, but instead flipped…
Captain Trojan
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57
votes
3 answers
Is there a physical limit to data transfer rate?
Is there a physical limit to data transfer rate (e.g. for USB $3.0$, this rate can be a few Gbit per second)? I am wondering if there is a physical law giving a fundamental limit to data transfer rate, similar to how the second law of thermodynamics…
Shing
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57
votes
3 answers
Why do we use AC for long distance transmission?
Why do we use AC (Alternating Current) for long distance transmission of electrical power?
I know that AC is such a current that changes polarity (magnitude and direction) and has fixed poles.
EiNsTeIn
- 703
52
votes
3 answers
Why do we use Root Mean Square (RMS) values when talking about AC voltage
What makes it a good idea to use RMS rather than peak values of current and voltage when we talk about or compute with AC signals.
anilkumar
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52
votes
8 answers
Difference between live and neutral wires
In domestic electrical circuits, there are 3 wires - live, earth and neutral. What is the difference between the live and neutral wires?
As there is AC supply, it means that there are no fixed positive and negative terminals. Current rapidly…
45
votes
8 answers
How do headphones and earphones produce good bass if tiny speakers can't produce low frequency sounds very well?
It's a well known fact that small/tiny speakers cannot produce low frequency sounds very well. Conversely, large speakers cannot produce high frequency sounds very well. Hence the need for tweeters and woofers in your speaker systems.
But, how do…
navigator
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36
votes
7 answers
Why can't you hear music well over a telephone line?
Why can't you hear music well well over a telephone line?
I was asked this question in an interview for a university study placement and I unfortunately had no idea.
I was given the hint that the telephone sampling rate is 8000 samples per second.
Danny Rancher
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33
votes
5 answers
How is data transferred between devices?
If you send a text from your phone to your friend, do electrons move from your phone to your friend's phone? How is text transferred (physics wise)? I am a programmer and I want to know how it is working.
Adm Kuznetsov
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27
votes
1 answer
Why don't they use springs as an energy source for cell phones?
I know they used springs for clocks way back in the day and now it's all lithium ion batteries.
For reference, consider the Iphone that has a battery with a capacity of 5 Watt hours (18,000 joules).
For portable energy sources, fuel cells have been…
Klik
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26
votes
6 answers
Quantum random numbers from a laser -- simplest setup?
I'm a software / maths guy who would like to build a physical setup for generating quantum random numbers. I have no physics background, so bear with me.
Background
The project is for a public exhibit, so it's important to me that the setup should…
helveticat
- 371
23
votes
11 answers
How do computers store sound waves just by sampling the amplitude of a wave and not the frequency?
All of this just doesn’t make sense though.
I mean, doesn’t the amplitude represent the loudness and the frequency the pitch? Aren’t they completely independent from each other?
Is the book just lacking information or am I just not getting…
RedP
- 411
21
votes
3 answers
Can the speed of light inhibit the synchronisation of a power grid?
As far as i know the following are true:
for a power grid to work properly, the voltage supplied by all the generators has to be relatively synchronised at every point in the grid, especially at the generators themselves.
changes in electric…
jucom
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20
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2 answers
Does a Mobius resistor have zero inductance? How would you calculate the inductance?
Wikipedia describes a Möbius resistor as follows, and the Patent for this device gives a similar description.
A Möbius resistor is an electrical component made up of two conductive surfaces separated by a dielectric material, twisted 180° and…
Truth
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18
votes
6 answers
Why is electrical energy so difficult to store?
Does anyone know a general answer to these questions? (I've asked them together because they're all pretty related, it seems.)
Why is it that we find electrical energy so difficult to store? Do we just find energy difficult to store generally?…
user27182
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17
votes
2 answers
Why is Near Field Communication (NFC) range limited to about 20cm?
Near Field Communication (NFC) operates at 13.56 MHz.
Near Field is the region situated at a distance r << λ
λ = c/f
c = 299 792 458 m/s in the vacuum.
f = 13.56 MHz = 13.56*10^6 Hz
λ = 299.8/13.56 = 22.11 m
Of this distance, the Reactive Near…
Mister Smith
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