# Tag Info

16

The problem is that the two calculations have hardly anything to do with one another - so it's no wonder you don't get the same result. The electron volt, as you say, measures the work you need to move an electron across a potential difference of one volt. On the other hand, if you want to calculate the mass of an electron using $E=mc^2$, what you need is ...

13

Another term is thermal resistance, This is incorrect. Thermal resistance is something that prevents heat flow. It is an entirely separate concept from electrical resistance. How is contact resistance explained? To obtain very low resistance in a material like most metals, the electrons must be delocalized from the individual atoms, and free flow ...

6

Electricity needs charges particles (or quasi-particles) to conduct. Heat can be conducted with almost any quasi-particle. Diamond is one of the best conductors of heat in existence, and it's because of phonons, ie quasi-particles of lattice vibrations, which are strong because the diamond lattice is strong.

5

This is a very interesting question, especially considering the very recent history of scholarship on electrical contact resistance (a term first coined in 1964 by William Shockley, one of the inventors of the transistor), as well as thermal contact resistance. For the following explanation, I will use this research paper on electrical contact resistance ...

4

I have seen lightning hit the middle of a sea lake. ( very happy I had not gone swimming). The water did not boil enough to be observed at my distance, about 500 meters. No dead fish were washed out. A boat or a head in the sea water will become a focus for the upward streamers that will join the downwards leaders and form a path for the energy of the ...

3

Because so many different power generators are connected to the same mains circuit, it is extremely important that all generators maintain the same phase (and thus frequency) of the power supply. This makes the 50 Hz (or 60 Hz, depending on what continent you are on) a rather reliable reference signal. In this website the question of mains power stability ...

3

The charger accepts one voltage as its input, and produces another voltage as its output. This could be done with a transformer or any number of other conversion techniques - for example, in a switched mode regulator the voltage is connected very briefly to charge a capacitor, then disconnected again. It keeps repeating this to keep the output at the right ...

2

Your fillings are either gold / palladium inlays or silver-mercury amalgam. The composite or enamel fillings don't apply here. Welding fillings together will require that you have fillings in opposing teeth. It is certainly possible to weld metals together with a brief electrical current - it's done by robots in car factories every day. However, it requires ...

2

When one says that bulb is 100-W, does that mean it is 100-W at 120V, which would tell me the resistance of the bulb? Somehow I have to find the resistance of the bulb which is not given. Recall that, for a resistor, the AC power dissipated is $$P_R = \frac{v_{rms}^2}{R}$$ Assuming the voltage across the bulb is not significantly reduced by the ...

2

Power: $$P=VI$$ Ohm's law: $$V=RI$$ Resistance: $$R=\rho \frac{L}{A}$$ These should be what you are looking for.

2

The lightning only 'sees'positive and negative charges. If the storm clouds are negatively charged then they drag a positive charge along the surface of the ocean. When the charge reaches a certain capacitance a lighting strike will neutralize the potential. Like some people, the strike follows the path of least resistance; which is usually the highest ...

2

Electrons do not "decide" which path to take in any meaningful precise sense (they don't take any particular path at all unless an interaction fixing their position takes place every step along the way), hence there is no time span in which that decision is made.

2

I guess the answer you are looking for is that the electric field propagates at the speed of light. Suddenly add a voltage source to a complete circuit and the electric field will spread at the speed of light $c$. Depending on how far away a specific electron is in the circuit, this electron will soon feel this electric field and then immediately react to ...

2

The temperature of the circuit can probably be crudely modeled by assuming that you have two channels: one for heat absorption, and one for heat loss. Heat loss Suppose you have something like a light bulb. The hot filament loses heat via radiation and conduction. Let's focus on radiation. The rate of heat radiated by an object of temperature $T$ depends ...

2

Lightning branches so that it can reduce the resistance of the path it takes to the ground. As you know, when you attach two identical resistors in parallel, the equivalent resistance is lesser than that of the two in series. Branching essentially does that. It creates more and more parallel paths by which the electrons can flow, thereby reducing the total ...

1

The blade geometry and structural stability is less meaningfull when you have more blades. Means; if you have to to build the blades only from direct cutted materials without any airfoil-shape you have to use more blades. Thanks to Betz law, this doesn't even change the efficiency too much, and it's more or less only a investment cost factor. And, ...

1

Your answer appears to be correct, bar the lack of any electric charge in your formula. If the applied force is solely due to a cosinusoidally varying electric field at a given position (you can ignore the magnetic component of the Lorentz force only if the charge moves non-relativistically), then so is the acceleration. Integrating this with respect to ...

1

Looking up "what happens when lightning strikes a house" on google (it is a .php file so I had to use printscreen) See also this youtube video. So yes, avoid taking a bath during a close by storm. Have a look at this answer What will happen when lightning strikes on the surface of the deep sea? which has some numbers of the energy in a strike. By the ...

1

Rather than call it "electricity", I would prefer "current". But you are correct. For a disconnected segment, the amount of time the current will continue to flow depends on the capacitance, the resistance, and the starting current. For for your average "disconnected wire", the capacitance is quite low and resistance is such that there will be very little ...

1

Are you speaking specifically about currents in wires? If you look at (the simplest version of) Ohm's law you will see that $\mathbf{J} = \sigma \mathbf{E}$, where $\sigma$ is the conductivity (technically it's a tensor, but we'll assume a constant scalar for now). In this case, $\eta$ = $\sigma^{-1}$, which is the resistivity. Thus, we can show that ...

1

You should look at an electric circuit a like a river or a water slide attraction in an amusement park (see my little artist impression below). The resistors are the steep parts: that's where the potential energy is lost. The wires are the horizontal parts, so there no potential energy is lost. But as the water is already moving, it doesn't stop moving in ...

1

First, if you ground a magnet into powder, then the tiny resulting magnets would rearrange themselves into the lowest possible energy state, and that's with each N pole matching with an adjacent S pole. Yes, you could guess you'd get one long line of magnetic particles lining up into a long thin magnet, but then the next line over would line up in the exact ...

1

DC current is organized as following: positive potential applied to one end of the wire, negative potential applied to the other. Electrons move from one end to another with some speed. If you have one electron in vacuum and electric field from A to B, then there will be force acting upon that electron due to $F=eE$. Movement should happen along line ...

1

First, do not put them "in series"! Each is powered from the mains ie they are in parallel. Second, earthing is typically applied to any external metalwork that anyone might come into contact where there is any danger of the live coming loose and touching that metal. Think worst case fault conditions. Finally, the fact you have to ask these question means ...

1

When a motor moves it also acts as a generator and the current trough the windings is given by the difference of the external voltage and the induced voltage. When the motor stands still, though, the generated voltage is zero and the windings will draw the max. current they can based on their DC resistance. In other words, the faster the motor runs, the ...

1

Point particles as the electrons (which are the charge carriers) move according to Newton's law $\textbf{F}=q\textbf{E}=m\textbf{a}$. Whenever an electric field is present it generates a difference of potential between two points $A$ and $B$ given by its differential form calculated between the two points  V_A - V_B = \int_A^B \textbf{E}\cdot d\textbf{s}. ...

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