64 votes
Accepted

Is there a physical limit to data transfer rate?

tl;dr- The maximum data rate you're looking for would be called the maximum entropy flux. Realistically speaking, we don't know nearly enough about physics yet to meaningfully predict such a thing. ...
  • 4,573
61 votes

Is the voltage ever undefined?

The voltage between to points in the universe is always defined. But the voltage between two circuits is undefined because (at least from electronics point of view) circuits are abstract models of ...
  • 631
53 votes

How is data transferred between devices?

It is less of a "sending electrons," and more of jiggling them. Think of a wave, done by the crowd at a sporting event. One person raises their hands high, and then sits back down. The ...
  • 43.2k
44 votes

How do headphones and earphones produce good bass if tiny speakers can't produce low frequency sounds very well?

There are a few reasons why small speakers have trouble creating bass. Bass is directly proportional to the amount of air the speaker can move. So you want a large cone that can move a large distance....
  • 3,486
34 votes
Accepted

How electrons move so fast in a electric circuit?

The electrons themselves don't move all that fast. The wave energy is the part that moves quickly. Picture it this way. You have 500 meters of pipe, with a small hole at the other end. The pipe is ...
  • 2,736
33 votes

Is there a physical limit to data transfer rate?

The Shannon-Hartley theorem tells you what the maximum data rate of a communications channel is, given the bandwidth. $$ C = B \log_2\left(1+\frac{S}{N}\right) $$ Where $C$ is the data rate in bits ...
  • 461
31 votes

Does a Mobius resistor have zero inductance? How would you calculate the inductance?

The inductance can be calculated, but it is first necessary to look at the behavior at very fast timescales of a ns or so. Clearly the two faces of the strip form a transmission line and so, at short ...
  • 559
28 votes

Why does a capacitor act as a frequency filter?

An capacitor has one intuitive property: Its voltage can't change instantly since its voltage is dependent on the charge it has stored, and charge doesn't move at infinite speeds (there is always ...
  • 7,785
27 votes

How is data transferred between devices?

I have drawn a diagram to illustrate the mechanisms of how telecommunications work. This is a highly simplified cartoon of what happens. What I’ll be describing is in part often described in Telecom ...
24 votes
Accepted

Are neurons more energy efficient than transistors?

Not surprisingly, it isn't so easy to get the power consumption of a cell. What is the power consumption of a cell? makes various estimates. One estimate for a human cell is $$P_{cell} = 3 \cdot 10^{-...
  • 28.2k
24 votes
Accepted

Why is it easier to raise AC current to high voltage than DC?

Changing the Voltage of AC can be done with a simple iron core transformer. That's a simple device without moving parts that only consists of a magnetic core, copper wire and some isolation (...
  • 712
17 votes
Accepted

Is the voltage ever undefined?

Is the voltage ever undefined? The voltage, or potential difference, between any two points is always defined. It is defined as the work per unit charge required to move the charge between the two ...
  • 58.2k
16 votes

Is the voltage ever undefined?

I interpret that statement as "the voltage difference between those two disconnected circuits cannot be solved for using Kirchhoff's laws".
15 votes

How is data transferred between devices?

All I really have to add to the other answers is to provide some context to complete the picture. You probably know that when you send something (like a text, or a web request) over a network, it is ...
14 votes

How electrons move so fast in a electric circuit?

In fact, electron's speed is not so fast that light bulb glows up immediately. It is the electromagnetic field which travels in the circuit at near the speed of light that is resposible for it. ...
11 votes

Why does a capacitor act as a frequency filter?

What is the physical behaviour which allows a capacitor to act as a high or low pass filter? A capacitor alone cannot act as either. To create a filter you need a combination of resistance and ...
  • 252
10 votes

Is the voltage ever undefined?

I want to elaborate a little bit on what several comments and answers have stated: Undefined from an engineering perspective is different from undefined from the physics perspective. An electrical ...
10 votes
Accepted

Do electrical appliances reduce the heating bill?

They do reduce the heating bill, but.. Let's see some numbers. The average power consumption of (i) a fridge is 50-100 W, (ii) a television is 50 W, (iii) a laptop is 50-100 W etc. Average power ...
  • 4,840
9 votes
Accepted

What is meant by phase coherence of electrons?

Strictly speaking, a phase coherent electron device is an electronic device whose dimensions is smaller than the phase coherence length of the electrons. This definition is the one adopted in ...
  • 9,905
9 votes
Accepted

Why does a capacitor act as a frequency filter?

Imagine electricity as water in a pipe. The current can flow in either direction (direct current, DC) or one way then the other way (alternating current, AC). Now put a rubber membrane in the pipe. ...
  • 106
9 votes
Accepted

Radio receivers and the loss of electrons

Here is a circuit diagram of a very simple crystal set and there is a return path for electrons. $L$ and $C1$ form a parallel resonant circuit the output of which is rectified by the diode, $D$, and ...
  • 80.8k
9 votes

How do headphones and earphones produce good bass if tiny speakers can't produce low frequency sounds very well?

It's actually because headphones/earphones are placed in directly contact with your ear and so the sound waves do not need to travel far. The intensity of sound decreases as $(\frac 1r)^2$, and so ...
  • 25.8k
9 votes
Accepted

In the equation below for root mean square voltage, I don't understand how the $1/T$ came in, and how that equation was even derived

The average or mean value of $f(x)$ over a relevant interval is $$\frac{\int f(x)\, dx}{\int dx} .$$ For a sinusoid that repeats every period, it's enough to integrate over the period, as any ...
8 votes

Why two separate batteries in a circuit don't work?

The short answer is that you need a complete circuit for a battery to work. However, I find a longer answer to be very useful to help with understanding. If you have a circuit, you are solving a ...
  • 43.2k
8 votes
Accepted

How come a mobile phone signal is blocked by aluminium foil, but Wi-Fi gets through?

A matter of thresholds The reality of spread-spectrum is complicated but let's imagine that the WiFi router and cell phone tower have both allocated 1 Watt to transmit to your phone, and it in turn ...
  • 6,655
8 votes
Accepted

Why does my TV screen stay dust-free while other screens do not?

It is unlikely that the electronics of the device is responsible for that. The times of high static voltage in TVs are long gone. The only electronic thing I think could be responsible for that is ...
  • 6,965
7 votes

Pn junction voltage drop?

1) If the n and p doped regions are externally connected using a perfectly conducting wire, why will not any current flow? In thermal equilibrium no current can flow if one connects the two sides of ...
7 votes
Accepted

Why doesn't the Earth's magnetic field affect electronics?

Well, it does. The Earth's magnetic field is about half a gauss, or $0.5\times10^{-4}\rm\,T$. So if you have a meter of wire carrying one ampere of current from east to west, it'll feel a magnetic ...
  • 75.7k
7 votes

Capacitor in a superconducting circuit

To take your question at face value: what if we somehow connected the two ends of a charged capacitor with an ideal wire, that somehow avoids having self-inductance or radiation losses or anything? ...
  • 16.8k

Only top scored, non community-wiki answers of a minimum length are eligible