New answers tagged

0

Yes, you are correct. The potential difference between the plates remains the same, so the charge is increased by the same factor as the capacitance is increased - let's call this factor $k$ and let the dielectric have relative permittivity $\epsilon$ and fill a fraction $f$ of the plate separation $d$. So $V = Q_0 d/\epsilon_0 A$, where $A$ is the plate ...


0

You can think of the capacitor (when the dielectric is inserted) as being 2 separate capacitors in series: one of width $d$ and the other of width $(L-d)$, where $d$ is the width of the dielectric material and $L$ is the separation of the two metal plates. If you have two capacitors, 1 and 2 in series, the effective capacitance is $$C_{eff}=\frac{C_1C_2}{...


0

To make things even more confusing, there is a sense in which we could assign the vacuum a "resistance" of 377 ohms: https://en.wikipedia.org/wiki/Impedance_of_free_space


-1

Have anyone analyzed exponential solution of wave equation for displacement vector of a planar wave in vacuum ? Remember (using LaTex code) $\vec{D}=\vec{P}+\epsilon_0 \vec{E}$ and, also remember that $\vec{P}$ is a symmetric colinear field, this is a field constituted by pairs of vector with same modulus but oppositely directed on same straight line. Fact ...


2

1) It is necessary for a plane EM wave. If one assumes solutions to the Maxwell's equation to be plane waves, it is not hard to show that $\vec B \cdot \vec E = 0$. Namely, take the third Maxwell's equation and dot both sides with $\vec E$. $$\nabla \times \vec E = - {{\partial \vec B} \over {\partial t}}$$ $$i\vec k \times \vec E = i\omega \vec B{\rm{...


0

As an example of how silly this is let's say you like to eat hot food (at least, hot enough not to die of food poisoning assuming you eat meat, and you cook it with a microwave which consumes 1,000 watts, which you run for ten minutes a day (three meals, three minutes per meal). I'm assuming that a microwave is the most efficient practical way of cooking ...


0

Some idea of how wildly ambitious these claims are can be gleaned from a BBC TV programme that was broadcast about six years ago. In this show, they put a family of four in a house for a day and powered it through pedal power; they needed scores of cyclists. The show is no longer available directly from the BBC, but this clip gives you some idea. ...


1

Under the scenario you presented, all you've done is made a bigger battery. Which is just sitting there, so there is no current flow. If you open up a standard 9 volt rectangular battery you will find six 1.5 volt cells connected in series, i.e. exactly as you described.


9

A human can produce about 100 W power continuously. That is equivalent to a couple of lightbulbs. So, while pedalling continuously you can keep one room reasonably lit. In one hour, that means you can generate a total energy of 0.1 kWh. A top athlete will be able to do better, so let's say it is possible to generate 0.2 kWh in 1 hour. That is still nowhere ...


0

You are right in both respects : This is a very poor question, expecting you to guess what might have gone wrong. There could be several explanations : bulbs with different resistances, or different ways of connecting them. The question is wrong. Your logic is correct in both cases. So either (a) there is some other valid reason in the question-setter'...


5

None of the above. Electrons are negatively charged, always. They do not become positively charged under any circumstances. In DC circuits they flow (or rather 'drift' at about 0.1 mm/s) only in one direction, from the -ve terminal to the +ve. In AC circuits they flow forwards and backwards in the wire, changing direction 50 times per second. They don't ...


1

Potential difference (or voltage) is equivalent to a pressure difference in a pipe system of water. If there is equal pressure at two points, then no water has any reason to move. If there is a difference, water flows (is pushed) towards lower pressure. Similarly, charges will want to move towards the point of lowest possible potential. The larger the ...


0

Electric current is due to the flow of free/conduction electrons in a conductor. By convention the direction of current is chosen as in the direction opposite to the flow of electrons. At any instant, the number of electrons leaving the wire is always equal to the number of electrons flowing from the battery into it. Hence, the net charge on the wire is ...


2

If one understand "carry particle" in the meaning that the particles move with the same velocity as the photons, than clearly no: Photons by itself could not carry particles. Photons move with the velocity of light $c$ and massive particles could not be accelerated to this velocity. This is both an observation and the basis of the Special and General ...


2

Good question :-) In the "ancient" times there was this old problem about the particle-wave duality. At the time, there was a Pilot wave theory, on which the particles and the waves are also different entities in some interaction. But it didn't live too long. Probably it failed some sophisticated experiments. On the current theory, there are fields, and ...


0

Clearly, the water may be in direct contact with the 220 or 230V phase line voltage inside the shower head. But normal tap water has a high resistance, and this resistor (of the water touching the body) is in series with a user's body resistance. It is not (directly) the voltage that is dangerous, but the resulting current that may flow through the human ...


2

1) Electric flux lines model helps us to understand the behavior of an electric field much simply and it's pretty easy to visualize it. The definition of electric flux is the number of filed lines passing a given area normal to it. The field lines show the direction and magnitude of electric force at some point. The density of field lines at some region of ...


0

Electric flux is a useful mathematical concept which gives us a measure of how much the field flows through an area which is positioned within the field. Consider a surface of area A which is perpendicular to an electric field E. The flux is given by EA. The larger the electric field, the more the field 'flows' and therefore the larger the flux. Similarly if ...


1

By analogy, you are comparing the properities of a solid material, in your first paragraph, to a gas mixture, the atmosphere, in the second. So the path taken would flow through the "weakest" or most conductive sections of air. No matter how small a volume of air you take, the conductivity/ionisation path is very unlikely to be consistent enough to ...


0

I'll answer your question in three parts. "What is the average range of voltage in sky?" I would hope that for sunny skies, it's near zero - otherwise it'd be nothing but bolts from the blue all day long. But I assume that you're talking about the average range of voltage in regular lightning. NOAA says that we have .1-1 billion volts in lightning. "I ...


2

Typical domestic electricity consumption is 3,300kWh per year, or about 64kWh per week. Gas consumption is 16,500kWh per year; if you do not have a gas supply, your total power consumption would be about 380kWh per week. The maximum current which can be drawn per house from the mains is 100A. This is set by a fuse installed by your supplier close to ...


3

While the paper linked to in sammy's answer does provide an equivalent circuit (page 5988), it seems of little practical use, since even in (unstable) equilibrium the current in L2 rises linearly with time. Within seconds (at most) it will reach a limit: saturation of the transformer core or maximum current (either I=U/R where R is the resistance of the ...


0

I think the point made is that the kinetic energy of the electrons (or other charge carrier) will normally be far higher than $kT$. That's because although collisions with the lattice are frequent the electron loses very little energy with each collision. The point being made is that in a collision between a light object and a heavy one very little of the ...


2

The following paper is devoted to electrical analogues to mechanical oscillators. Fig. 6 illustrates a simple coupled LC circuit which imitates the inverted pendulum on a cart given in Fig. 5. It does not include a circuit to balance the 'pendulum' as in the video. https://core.ac.uk/download/files/508/12941830.pdf I also found the following which may be ...


0

Electric current is not a flow of energy; it's a flow of charge. Charge and energy are two very different things. An electric current is a flowing motion of charged particles, and the *particles do not carry energy* along with them as they move. A current is defined as a flow of charge by I=Q/T; amperes are coulombs of charge flowing per unit time. The ...


5

Strictly speaking, yes, I believe neutral atoms have an electric field (though very weak). For example, if you have a hydrogen atom in the ground state, the absolute magnitude of the wave function of the electron decreases exponentially with radius (for a sufficiently large radius), so there is a (very small) positive total charge within a sphere with an ...


11

In an atom the electrons do not have a position. They are delocalised over the whole atom and in the absence of any external field this results in a symmetric charge distribution. So an isolated neutral atom is spherical and has no external field. However if you bring two atoms near each other then their charge densities will develop fluctuations that are ...


6

Atoms are in the quantum mechanical regime. The electrons around the nucleus occupy orbitals ( not orbits) i.e. probability loci where a measurement will find an electron. These orbitals have quantum numbers that give them shape. When the angular momentum quantum number l is equal to zero, the orbital is isotropic and neutrality is maintained. But for ...


-1

Units are political. But one who is accustomed to seeing amperes can argue they are easier to use in real life.


2

Can Light Really be Matter? I suppose it depends on what you mean by "be". Matter will be created from light within a year, claim scientists It just is counter-intuitive to me. This is the fallacy of reasoning from personal incredulity. It isn't a good guide. I find most of QM and relativity counter-intuitive - it doesn't seem to be a simple ...


0

Interesting question. Light isn't matter. Matter is generally described by fermions, light is described as a boson. These are different. Though they have qualities in common, for example energy or mass or spin. Interestingly, Heisenberg judged that energy was 'equivalent' to the ancient principle of fire.


6

Initially, when first glass rods were systematically being rubbed, the "charging" phenomena was observed. The electric charges were hypothesized to be positive and negative, and the pioneer (Franklin? forgot the name...) pretty much arbitrarily decided to call one positive and the other negative. Further experiments helped him deduce that two like charges ...


16

The Hall Effect shows that negative charge is moving. In the Hall effect, one passes a current through a wide strip of metal exposed to a perpendicular magnetic field. If positive charges moved, we'd expect the positive charges to be travelling in the same direction as $\vec{I}$, and the magnetic force $q\vec{v}\times\vec{B}$ would be to the right. Thus, ...


11

Physics's don't know that only negatively-charged particles move. We can create ion currents on demand in many environments. We do know that the current flowing in a metal wire is negatively charged particles in motion. As for how to determine that, you do a Hall effect measurement. The measurement works by subjecting a current in a relatively wide bar to ...


0

You're simply asking about Faraday's observations and law: a time varying magnetic field "produces" an electric field and this production is described precisely by Faraday's law: $$\nabla\times \vec{E} = -\partial_t\,\vec{B}$$ It may be more familiar to you in its integral (but altogether equivalent) form: $$\oint_\Gamma \vec{E}\cdot\mathrm{d}\vec{r} = -\...


0

As you point out, an oscillating electric charge (and by that I assume you mean a charge moving back and forth) generates both an oscillating electric field but also an oscillating magnetic field. This is straight forward to understand from the fact that charge in motion produces a magnetic field. This is also built in to Maxwell's equations (that describe ...


4

Technically "potential difference" is the difference in electrical potential, i.e. $\Delta V$, not the difference in electrical potential energy, $\Delta U$. Potential difference ($\Delta V$) is also called voltage, in certain contexts. However, many people and sources are sloppy about their terminology, and they will say just "potential" when they really ...


0

I asked my physics teacher, and the reason very little current (if any) is induced is that hysteresis in the core means it will quickly become saturated if the direction of magnetic flux does not change, and hence the secondary coil will not experience change in flux.


1

Courtesy of AnnaV : By heating cord your book probably means the wire or flex which conducts electricity from the power supply to the heater. This is made of copper because it has very little resistance to current, compared with the resistance of the heating element, which is very high. The electrical power dissipated in a resistance $r$ when current $I$ ...


2

Among competing hypotheses, the one with the fewest assumptions should be selected. Some electrified objects repel, some attract. This can be explained by two kinds of charge. Nothing that cannot be explained by two charges can be explained by adding a third kind of charge. So we continue to describe electricity as occurring in two kinds.


1

If you had one sweaty hand on the isolated circuit, and one bare foot on the wet Earth, there would be no path by which current could flow through your body, and return to the isolated circuit. A (probably) trivial amount of current could flow because of the AC voltage, and (probably) very weak capacitive coupling between the Earth and the circuit. But, I'...


0

1) Maybe this could provide you with some insight. This is from Griffiths Electrodynamics 3rd Edition. I'm not sure why the solutions you've found require the cosθ′ but this one doesn't include it. 2) When using spherical coordinates and trying to outline a full sphere, theta outlines a half-circle (existing in the xz plane), phi then rotates and ...


5

There are some good answers here, but I think I want to try to abstract Franklin's work a little bit. Because Franklin found just two options - "repel" and "attract", he was forced to consider only two kinds of charges. Consider the experiment, where glass-glass repels, plastic-plastic repels, and glass-plastic attracts. If all glass is the same, the glass ...


25

I agree with DanielSank that the question is asking (wholly, not partly) about the historical development of the concept of electrical charge, not our modern description of it - "how did they know?" not "how can we know?" The latter (answered by dmckee) is the end result of more than two centuries of observation, experiment, theorising and debate, and ...


3

Let's assume we don't know how many types of charges exist. But we know that there are bodies which either attract or repel each other. Now we perform an experiment We find all such bodies that repel each other and put them in separate categories. After extensive experimentation we observe that they only belong to two piles. Furthermore we also observe ...


0

I could be wrong, but there is a phenomenon in physics called quantum superposition. To briefly explain it, an electron can be in all possible allowed places at once until it interacts with another particle causing, in laymen's terms, the universe to "observe" it. When a circuit is closed, the free electrons are given a specific path in which they may go, ...


42

Get together a collection of charges. As many different ways to generate a charge as you can think of. Go ahead and invite your friends so they can think of some more. (As a practical matter you make static charges just before you use them, but still...) Now, test them pair wise to see if they attract or repel one-another. Keep careful records. Find the ...


1

The picture is correct. By the passive sign convention, the reference direction for current is into the positive labeled terminal of the circuit element and thus the circuit element is absorbs (not necessarily dissipates) power when the product of the voltage across and current through is positive. However, the reference direction for $I_S$ is out of the ...


3

Please note that this is not so much an answer as an extended comment. At this website (which is the Google Book website for Contemporary Newtonian Research by Z. Bechler) it says It is well known that Newton became convinced towards the end of his life that electricity played a vital role in the operations of nature. In the famous final paragraph of ...


1

there is an electric field inside the wire, and there is a loss of potential energy, or voltage as they move but this drop in voltage is usually negligible (thought not in some applications) and we only consider that the drop in voltage comes only from the circuits elements o loads. This idealization often fails not with the wires, but within the battery ...



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