# Tag Info

43

Electricity isn't a gas that expands out to shock anything in contact with it. Electricity is a flow from high voltage to low voltage. Touching a charged object is only dangerous if you become a current path--if it uses you to get somewhere. Even if the earth had a net charge, you aren't providing it anywhere to go, so you will not be shocked. It's somewhat ...

42

When discharging without a tool, the whole charge exits your body through a small skin surface area, say $0.1 \,mm^2$. When you hold a tool that surface is much bigger; perhaps $100 \,cm^2=10,000 \,mm^2$. That means that the current flowing through neurons in that area is much lower, and perhaps low enough as to not be felt. Pretty much the equivalent of ...

20

I'll answer the concrete question, because it's one of those fun ones where the units are all wrong and the scales are just absurd. Does this also mean that if I release a million amperes of current into the earth, every living entity walking barefooted should immediately die? It depends on how long you do it and with how much power. And ...

14

This gives me a feeling that a capacitor never gets charged fully. Am I right? Why not? In the context of ideal circuit theory, it is true that the current through the capacitor asymptotically approaches zero and thus, the capacitor asymptotically approaches full charge. But this is of no practical interest since this is just an elementary ...

9

Firstly we are not the best conductors, so current might be having a relatively hard time getting through us. But I believe the real reason is that you also need a high potential difference in order to get current flowing through you. Like lightning which needs a huge potential difference between the clouds and earth (so big that most of times a neutral ...

7

You will get a pretty good answer by reading this paper. In short: fat, water, and muscle each have different electrical properties as a function of frequency. By measuring the (very small, on the order of micro amps) current that flows between your legs when frequency of the driving voltage is changed, you can create a model of the body as parallel and ...

4

As others have mentioned, for all intents and purposes, yes it reaches %99 charge after 5 tau. However, as the current gets smaller and smaller as we reach full charge, technically it will never become 'fully' charged, even in practice. The current will continue to get smaller and smaller, until it is unmeasurable and therefore negligible.

4

A battery in a circuit normally sources electrons at the negative terminal and sinks electrons at the positive terminal. The chemical reaction at the positive terminal consumes them. The total number of electrons in the battery does not change. Similarly, a diode accepts electrons at the negative terminal and sources electrons at the positive terminal, ...

3

If you are seeing 4.5 volts across three batteries and 3.3 volts across two others, then the join you think you made is not a join. There is a common thing in electronics called a "cold solder joint". It usually happens when your solder is not quite hot enough when it touches the metallic surface - just the kind of thing that happens when you solder to a ...

3

The filament will be a reasonable approximation to a black body emitter, so it's spectrum will be given by Planck's law: $$B = \frac{2hc^2}{\lambda^5} \frac{1}{e^{\frac{hc}{k\lambda T}} - 1}$$ So just measure the radiance of the light from the filament for a range of wavelengths and do a fit to Planck's law by varying $T$. This will give you an excellent ...

3

To fully charge a capacitor to 5 Volts, say, you could connect it to a 10 Volts source until it is half charged, then connect it to your 5 V source. This is of courcse a ridiculous method, since you could hardly hit the moment of correct charge so precisely; any micorvolt error would start an exponential curve as in your original setup. That being said, ...

3

How can electrons travel in these beams if they repel? First of all, the picture you posted looks like lightning which is basically arcing, i.e., ionization of gas to create a conductive path. This is not what I would typically consider an "electron beam". To answer you question: Creating and maintaining the integrity of an electron beam is not easy. ...

3

A counterpoint to Schwern's answer (which was instructive, but I believe wrong on some key points - but I will borrow a couple of numbers from it). I think the correct way to pose the question is: If a 300 mA current for 100 ms will kill a human, what should be the rate of change of the electric field around the body to induce that current? Treating ...

3

From Wikipedia An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. The electrons are still there when you switch off the bulb.Its just that once you turn off the lightbulb there is no net force on the electrons and they whizz about in random directions constituting no net ...

2

The paper strips were ironed to make them flat and easy to stick to the CRT screen. Old CRT color screens used (IIRC) around 25kV to accelerate the electrons to excite the phosphors on the screen itself. This resulted in the buildup of a static charge on the inside of the screen, and a corresponding charge on the outer, with the glass acting as a dielectric. ...

2

You are touching something that has OV and the Earth which again has 0V. No potential difference there.So why should you have a current through you?There is no electric field to drive charges through you.

2

Electricity will only flow if there is a difference of voltage. If the earth, the object, and your body are all at the same voltage (lets call it zero volts) then there is no difference in voltage and hence no electrical current.

2

In brief: No. But to be safe you need a better appreciation than the wording of your question suggests. Numbers can be arbitrary Touching a point labelled 0V might kill you. Touching a point labelled 1000V might not - if no part of you is in contact with anything that isn't also also labelled 1000V, using a common reference point. From the perspective of ...

2

Without equations: The ideal dipole is made up of two oppositely charged particles infinitely close to each other. So we can immediately deduce that if the electric field does not change along the direction of the dipole, it exerts no force (because the force it exerts at the positive particle will identically cancel that at the negative one). The only way ...

2

My guess; you are mixing up quadripoles and quadrupoles. Quadripoles are two-port networks used in electric circuit analysis. The original German word is "Vierpol Theorie", which means Four-pol because of 4 Poles. https://en.wikipedia.org/wiki/Two-port_network Quadrupoles are related to multipole expansion used in electromagnetic, atomic orbital,.. theory. ...

2

The current is the conventional current in the opposite direction to the electrons current but they are the same thing , the current is the same in series connections. If the two lamps are identical they will give the same amount of light.

2

Since the lamps are in series, the electric current through each is identical; all of the current out of one lamp is in to the other lamp; if there is a flow through one, there is a flow through the other. It cannot be that there is a flow through one and not the other (in the context of this simple model). Thus, if the lamps are identical, their ...

2

As you walk across the floor, the soles of your shoes attract electrons from the carpet, and those electrons build up all over your body. The excess electricity wants to find a way off of your body, and when the doorknob provides a path of least resistance, the air between your hand and the doorknob expands, turns into a plasma, heats up, and pops as the ...

2

Static comes from the same root as stasis, meaning stop, immovable, To create static electricity, you have to rub two different materials. At the moment you rub them, the electrons already moved Note the word "create", creation is not static, and yes there are transient fields and currents during creation of a static field. The static describes the ...

2

Is there a fallacy in this statement? At least two. First, unless one is referring to a perfect (ideal, etc.) conductor, only in the electrostatic case does the electric field inside a conductor vanish. Second, in the case of an ideal conductor, there can be a steady current through without an electric field inside. Recall that an electric field ...

2

You are sloppy with units, but the result is correct. To go from 25C to 3C is 22 cal/g. When you multiply by 300 g you have cal and your conversion to kJ is correct. Converting to W-hr is silly, but that is the unit of energy, not W/hr. You have 8.3 W-hr you want to remove. That chills the water assuming no new heat is added, so insulate the water. ...

2

Q = mc(t1-t2), Now, m = (density)(volume), Specific heat of water, c(in joule/gramCelsius) = 4.186, Hence, you can find the energy it would require for this conversion. . And the work you do can be a bit more pertaining to your efficiency.

2

Theoretically yes, the laser principle does not consume any material. There is a light source that excites the electrons in the material to higher levels, they deexcite to some intermediate one, here the avalanche of photons appears producing the laser light and leaving the electrons in the ground state. And you can repeat the process without a loss.

2

You really are asking two questions. First - how do we calculate the temperature: At the typical temperatures of a halogen bulb, the large majority of heat loss is due to thermal radiation (although there is some conductive loss in a halogen bulb as the bulb is not evacuated). Because of this, the most important factor is the "apparent size" of the ...

1

Any force that involves electric or magnetic fields uses the Lorentz force equation: $\textbf{F} = q(\textbf{E}\times\textbf{B})$ An electrostatic force comes from a static electric field, such as the one generated by a charge at rest. This force is given by $F=q\bf{E}$ since the magnetic field is zero. Electromagnetic force comes about from the same idea, ...

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