The study of the presence and flow of electric charge. Charges, currents, fields, potentials.

learn more… | top users | synonyms

7
votes
1answer
2k views

What’s the relationship between thermal radiation and Johnson thermal noise?

All objects above absolute zero emit radiation due to random collisions between the atoms they are made of. The spectrum of radiation emitted varies according to the temperature of the object, I ...
7
votes
4answers
828 views

Why does electric field intensity $E$ can be uniquely determined by its divergence and curl? [duplicate]

My question is, the number of following equations $$\nabla\cdot E=\frac{\rho}{\varepsilon}$$ $$\nabla\times E=-\frac{\partial B}{\partial t}$$ is 4 while the number of unknown variables $E=(E_1,E_2,...
7
votes
3answers
9k views

Where do electrons in electricity come from?

Where do the electrons come from when an electric generator is making electricity? Is from the air? Would a generator work in a vacuum? Electrons have mass so where would they be pulled from if ...
7
votes
2answers
2k views

Does Tesla's photoelectric “solar cell” really work?

Tesla patented a device for gathering energy from light, using the photoelectric effect. (US 685,957 - Apparatus for the Utilization of Radiant Energy): Basically just a sheet of "highly polished ...
7
votes
5answers
4k views

Why does a faraday cage protect you from high currents?

In an electrostatic case it is clear that that in a space enclosed with a conductor (without charge in it) the electric field is zero. This is often demonstrated in physics shows like on the ...
7
votes
3answers
3k views

When mutual inductance is occurring between two coils, is self inductance always occurring in each individual coil?

When a coil connected to an AC generator creates an EMF in another nearby coil (mutual inductance), is self inductance simultaneously occurring in both coils?
7
votes
4answers
10k views

Why does the current stay the same in a circuit?

I was informed that in a circuit, the current will stay the same, and this is why the lightbulbs will light up (because in order for the current to stay the same, the drift speed of the electrons need ...
7
votes
1answer
194 views

What experiment disproved single fluid theory of electricity?

I just can't understand how history of electricity goes on. What experiment disproved Benjamin Franklin's fluid theory of electricity?
6
votes
4answers
19k views

Electrical force vs gravitational force

Given that the electrical force is so much stronger than gravitational force at atomic levels, why is it that it's the gravitational force between you and the earth that keeps you on the ground rather ...
6
votes
2answers
31k views

Why don't electric workers get electrocuted when only touching one wire? [duplicate]

I know that when electricians work on the poles on the streets, if they only touch one wire at a time they will be fine. However, from my understanding, the negative wire is connected to a large ...
6
votes
3answers
10k views

What happens if I throw a battery into water?

Today I have by accident thrown a AAA battery into a bucket of water. I fished it out of the water immediately (within 20 seconds or so) and nothing notable had happened and the battery is still full ...
6
votes
5answers
5k views

Is there a travelling speed of for electric field? If yes, what is it?

Consider two circuits containing a battery, bulb, switch and conducting wires but of length 1 meter in one case and 1000KM in other. When switched on at the same time both the bulbs glow ...
6
votes
4answers
1k views

Why is there an electric field in a wire even though it is a conductor?

If you take a perfect conductor, there cannot be a field across it since if there were, the particles would arrange themselves in a way to cancel out the field right? Yet, why does the same not hold ...
6
votes
7answers
5k views

Can electricity flow through vacuum?

People say yes, and give a wonderful example of vacuum tubes, CRTs. But can we really say that vacuum (..as in space) is a good conductor of electricity in a very basic sense?
6
votes
4answers
2k views

What is the current of a capacitor when the derivative of voltage is undefined?

This is from the textbook I am reading: I know this equation for capacitors: $$i=C\cdot \frac { dv }{ dt }$$ Here is my question: how can diagram (a) be allowed if the derivative of the voltage ...
6
votes
6answers
3k views

Why does electricity need wires to flow?

If you drop a really heavy ball the ball's gravitational potential energy will turn into kinetic energy. If you place the same ball in the pool, the ball will still fall. A lot of kinetic energy will ...
6
votes
2answers
761 views

How exactly does a solar flare cause a power line surge?

There are occasional large scale electrical blackouts caused by solar flares. Quebec Solar Flare Blackout My question is: what affects the severity of the problem? It obviously depends on the ...
6
votes
2answers
19k views

Why do two connected 1.5-volt batteries become a 3- volt battery?

Why two connected 1.5 volt battery become 3 volts? If one battery plus side is connect to minus side of another battery, there should be a current flow between them until no free charge move anymore, ...
6
votes
9answers
23k views

Why is the charge transferred by electrons and not by protons?

Charges are transferred by electrons which we all know. But why can't it be transferred by protons? Well, I searched on Google where I found similar questions already being asked on many sites. ...
6
votes
2answers
17k views

Capacitor circuits with light bulb

Let's say we have a normal circuit with a light bulb, with wires and a battery. When one places a capacitor in this circuit, how is the light bulb able to light up, even when the capacitor prevents ...
6
votes
2answers
8k views

how calculate resistance between two points for arbitrary resistor grid?

I need to calculate resistance in an electrical grid. Grid is a graph. Edges of a graph are resistors. How calculate resistance between any two vertexes for arbitrary graph? I know Kirchoff law and ...
6
votes
2answers
6k views

What is the difference between induced and motional emf?

At least from their names, it seems motional emf is induced, so what's the difference?
6
votes
2answers
1k views

Conservation of Energy in a Capacitor

Consider a parallel-plate capacitor in free space. A negatively charged point particle with initial velocity $v$ passes through the space between the pair of parallel plates (with an initial path ...
6
votes
5answers
1k views

How long would it take for electricity to flow from one terminal to other, via a 1 LY long wire?

Basically, how long does it take for electricity to determine there is a closed circuit and how does it know that the circuit exists? I'm curious to know how it knows there is a closed circuit at any ...
6
votes
3answers
465 views

Why does Joule heating not occur when no current flows through a conductor?

Joule heating happens every time when the conduction electrons transfer kinetic energy to the conductor's atoms through collisions, causing these conductor's atoms to increase their kinetic and ...
6
votes
6answers
22k views

Calculating engine starter’s energy use

During a discussion on start-and-stop vehicle technology some bloke began pushing the point that re-starting the car uses stored energy from the battery, which needs to be replenished by increased ...
6
votes
1answer
253 views

If increasing applying energy to an atom excites electrons, why does electrical conductivity decrease as temperature increases?

Applying energy to an atom makes the electrons jump up to higher energy levels. This is known as excitation. Electrons on higher energy levels are easier to remove from an atom than those on lower ...
6
votes
1answer
1k views

How much of current flows through a bird sitting on a power line?

I've been googling for hours and went through over a hundred answers. Now, some say the bird doesn't form a closed loop, some say the current is so small that it doesn't kill the bird. From as much as ...
6
votes
4answers
24k views

Can Gases conduct Electricity?

Liquid electrolytes ionize and hence a current can pass through them. So if a gas can ionize, can it conduct electricity too? If so, what are a few such gases?
6
votes
1answer
775 views

Is there something like the Poynting vector for hydraulic circuits?

The Poynting vector is a representation of the energy flux in electromagnetics, showing the amount and direction of power flow at different points in space. In electric circuits, the energy is not ...
6
votes
1answer
159 views

Is there mechanical strain on a wire along the direction of current flow?

The (attractive) magnetic force on two parallel wires can be seen by the two wires bending towards each other. This can be explained by the Lorentz force acting on the charges and the charges "pulling"...
6
votes
5answers
15k views

Potential difference (PD) and electromotive force (EMF) in terms of electrons?

I am trying to understand potential difference and electromotive force in terms of electrons. In the above 3 circuit diagrams the red shows (what I think to be) the distribution of electrons around ...
6
votes
2answers
2k views

Will I get a shock when I try to use my hair-dryer under water?

Occasionally people get killed in their bathtubs by having an electrical device such as a hair-dryer take the bath with them - in movies. It seems to be a common belief that this is realistic, even ...
6
votes
2answers
389 views

Shot noise at high frequencies (can it really be ideal white noise?)

Quantum shot noise (either optical intensity noise or electrical current noise) described by the noise spectral density of $2 e I$ (electrically) or $2 h \nu P$ (optically). So it is white noise. I ...
6
votes
2answers
784 views

Ionized Depletion Region, Why aren't those charged being excited?

Ok so I understand the PN junction, and how when 2 Semiconductor materials are placed together the Electrons will jump into the Holes near the junction creating a Negatively Ionized Atoms on the P-...
6
votes
0answers
65 views

Weird phenomenon on aluminum laptop casing [duplicate]

A couple of days ago I observed a phenomenon which I'm not sure I understand correctly. My brother-in-law has recently bought an ASUS gaming laptop in an aluminum casing. When the power supply is ...
5
votes
4answers
9k views

A circuit with no voltage difference, but current flowing

From Michael on Skeptics Stackexchange: How about a wire that's grounded? Safe to touch, right? WRONG. ...
5
votes
3answers
4k views

Do electric and magnetic lines of force physically exist?

As per my imagination any thing can't impose force on the other by not giving even a touch(i,e action at a distance). So I thought there must be some physical existence of lines of force. Although ...
5
votes
5answers
4k views

How does insulating footwear prevent an electric shock?

The reason I have always heard to explain the reduction of electric shock when we wear insulating footwear goes as follows: When electricity passes from our body to the ground, an electric circuit ...
5
votes
1answer
544 views

Why does the electron volt seem inconsistent with mass?

If I understand correctly, an electron volt is the work done when an electron is moved from a plate with a voltage of 0V to another plate with a voltage of +1V. This is represented by $V = W/Q$, or $W ...
5
votes
3answers
931 views

Why don't we use beta radiation for making electricity?

Why don't we use beta radiation to make our electricity? Since it is an electron being released/made, it would make sense to try and capture it. But, we obviously don't so. What am I missing in my ...
5
votes
3answers
749 views

Can electricity transfer radioactivity?

If a cable used to power something is exposed to a radioactive source will it over time make the entire cable radioactive?
5
votes
5answers
5k views

What voltages are used to “safely” shock someone (as in a carnival game)

I've had this debate with some coworks. What voltage (rough order of magnitute) is used to safely shock people? "Safe" is a vague term, but as an example, there are arcade games where you hold onto ...
5
votes
4answers
41k views

Why does connecting a battery's positive terminal to the negative terminal of another battery not create a short circuit?

This is a question regarding the physics behind the observation. I have guessed the answer to the question, but I may be wrong, so I want to wait for the responses before posting it. Some major ...
5
votes
2answers
1k views

Why doesn't a neon sign seem that hot?

I heard that neon signs contain plasma, why aren't they hot? is it because the electrons and ions do not hit the lamp's wall? Is it because it is non thermal plasma and electrons and ions are not in ...
5
votes
4answers
17k views

How can you have a negative voltage?

How can you have a negative voltage? I don't really understand the concept of negative voltage, how can it exist?
5
votes
5answers
14k views

Understanding the relationship between electricity and magnetism

I keep on hearing that magnetism is just another form of electricity and vice versa. If that's the case why can't we use magnets as batteries, and why aren't my batteries magnetic?
5
votes
3answers
860 views

How is Kirchhoff's voltage law understood in the water flow analogy?

I met the Kirchhoff circuit laws in the past, but now I'm trying to associate them with a practical representation to be sure to understand them. Let's start with the Kirchhoff current law: If I say ...
5
votes
2answers
7k views

How do stun guns not kill people?

Now, I've seen a lot of answers to this sort of question, but most of them provide answers that don't actually make sense from a physics perspective. As an example of such an answer, I've commonly ...
5
votes
4answers
19k views

Is it possible to flow current in open circuit?

As I know a battery is an example of a closed circuit where it can then produce electricity , electrons will flow from negative pole to positive. A chemistry representation of this battery is for ...