New answers tagged

0

Joule integral is actually used as parameter of fuse. There are two extremes for specifying the current carrying capability of a conductor. a) Over a long time, so all heat is lost to the environment. The current will be given for some permitted temperature rise. Typically this is the temperature rating of the insulation. b) Over a very short time, so short ...


1

The accumulation is due to difference in electric field at two points .HINT try relating flux and electric field for charge accumulation ${E} = \frac{J}{\sigma}$ where $j$ is the current density and ${\sigma}$ is conductivity


0

Short circuit current depends on the spectrum $S$ and the external quantum efficiency $EQE$ of the solar cell, $$ I_{ISC} = q \int_{E_1}^{E_2} S(E) EQE(E) dE $$ The number of photons usefully absorbed per second is equal to the short circuit current. Can you get the Physics of Solar Cells by Jenny Nelson from a library? This is a great book for introducing a ...


0

Current flowing through a wire does increase its mass, but the increase is minuscule, and it's not due to the increase in the speed of the conduction electrons. Those electrons behave in ways that are similar to the molecules in a gas, and we can successfully model many properties of metals using the Fermi gas model. In a wire with no electrical current ...


1

I don't think that the mass would increase significantly, because electrons move in a wire with a drift velocity of the order of 1mm/s, it is the EMF that is established instantaneously.


1

The center of gravity of the system will rise only as high on the right as it was on the left. Supposing that the rolling happens as designed, and the mass of everything other than the water is negligible, the center of gravity of the water will be the same on the right as on the left. The pendulum therefore won't reach the hook unless you lift it the rest ...


1

When electrons zip around in a wire, they occasionally collide with the atoms of the wire. As a result, the electron can impart some (or all) of its kinetic energy to the atoms of the wire. This causes them to vibrate. And it’s this vibration that is macroscopically seen as the heating up. Consider the atoms in the dielectric. They can be thought of as ...


1

Current trough a wire gets the electrons moving, ( I would not talk about traveling energy) they are slowed by bumping in atoms and get them to move or vibrate faster, which is heat. The stuff between the plates of the capacitor ist partly polarized, so the electric field has shorter ways, the same thing as getting the plates closer zigether.


1

The constitutive relationship of an ideal capacitor is $$i = C\frac{\mathrm{d} v}{\mathrm{d} t}$$ when voltage and current directions associated to the capacitor are chosen according to the passive sign convention, regardless of whether the capacitor is charging or discharging. If, instead, you chose the active sign convention, the constitutive relationship ...


0

I think all they are trying to really convey is that the power of an element (battery, load, resistor, whatever) is it's voltage multiplied by its current. As an example, i simulated your circuit using r = 0.01Ω, L = 50mH, R = 2Ω, and e = 12V. The circuit is closed at time t = 1ms. By the end of the plot it has essentially reached steady-state. The energy ...


0

According to Ohm's law Ir=V/Rt you calculate current in the circuit. At each resistor there will be a voltage drop equal to Ir*R. To find power dissipated on each resistor you multiply that voltage dropxIr.


4

Here is something to get you started. Firstly let's make a simple SPICE model for a single solar cell. We have a current source in parallel with a diode, we also have a voltage source which we will sweep to calculate the IV curve. Here is the spice model, * Single solar cell solar cell Isc1 0 1 390.30 d1 1 0 GaAs_diode vs 1 2 0 vcc 2 0 0.7 * Ideal GaAs ...


0

You cannot just say that a motor produces 184 pounds of force. Do you mean 184 foot pounds of torque, 184 inch pounds of torque, or what? In your formula you are giving a radius of the lever rod as 18 inches and applying 184 pounds at its end. This would be 184 foot and a half (18 inch) pounds, or 276 foot pounds of torque. This is extremely over rated for a ...


1

you have confused power (watts) with energy (joules). Watts x time yields energy, upon which your equation must be balanced.


2

No, it would not necessarily mean infinite. This is a classic mathematical misunderstanding regarding limits. If you have a fraction, $$\frac ab$$ and you let the numerator tend to zero, $a\to 0$, then the fraction might tend towards zero: $$\frac ab\to\frac 0b=0\; \text{ for } \;a\to 0$$ If you instead let the denominator tend to zero, $b\to 0$, then the ...


1

A compass needle is magnetized and will experience a force or torque when placed in an external magnetic field such as one produced by a nearby current carrying wire. The compass needle is said to have a "magnetic moment" which measures how magnetized it is, and therefore how strongly it responds to external magnetic fields. Sometimes, magnetic ...


2

Physics equations are models (or abstract descriptions) of observed behavior - and as such they make certain assumptions, and so their domain of applicability covers those scenarios where those assumptions are valid. Mathematically, when the distance is zero, you have a zero in the denominator, and the value at that point is, technically, not infinite, it's ...


-1

We are treating the charge as a volume charge density. Now you say that at any point why isn't the field infinite. It isn't so because exactly at that point the charge is zero. Why? Because a point has no volume and hence charge at that point is zero. Hence $Q = 0$ when $\Delta v = 0$ $\Rightarrow$ $\overrightarrow{\mathrm{E}} \neq \infty$


1

how do I calculate how much voltage and/or time I need to put a given charge on the material? If the material is not conductive, then it is difficult to put the charge across the material. Since charging up one tiny point doesn't really affect the rest of the material. So "how you do it" would be critically important to understand how long it ...


1

You charge an insulator (e.g. methyl methacrylate a.k.a. Plexiglas) by targeting it with a cathode ray. The abstract linked below quotes a value of 2 million volts. I remember this sort of thing was done in the ion implantation lab where I worked as a student years ago. Those voltages were lower, probably no more than half a million volts. https://www....


1

But if there is a resistance in the primary coil it will dissipate heat following $I^{2}×R$ (primary). For an ideal transformer energy is conserved. Power in primary = power in secondary. Therefore there can be no resistance in the primary coil or there will be energy dissipated (lost) as heat in the primary coil. So for an ideal transformer the primary and ...


1

Solar cells are photovoltaic devices: they develop a photo-voltage when illuminated. In this sense they bias themselves. But that is a very confusing way of thinking about the as components in an electrical circuit. To get useful power out of a solar cell you must apply forward bias. The optimum bias is at the maximum power point (peak of the dashed curve). ...


1

tl;dr: The diffusion length of majority carriers is on the order of 1000 km so it can be ignored as a useful device parameter. We can show this by looking at the rate question for bimolecular recombination. At constant temperature the law of mass action says that product of electron and hole concentration of any doped or undoped semiconductor is a constant, $...


2

There is more than one relevant potential difference. You must distinguish between the potential difference, $V_L$, across the load (i.e. the 'user' that we are aiming to supply) and the potential difference, $V_W$, across just the transmitting wires (of resistance $R_W$ taken together). The load and the wires are in series across the supply so $V_\text{...


1

If we decrease the current by a factor of 10 and increase potential difference by a factor of 10, the system loss (emitted heat) decreases This is incorrect. The power is given by $P=IV$, so if $I$ decreases and $V$ increases by the same factor then power remains constant. the system loss (emitted heat) decreases following the formula 𝑃=𝐼2𝑅. But ...


0

Current generally prefers to flow more through the part of the circuit which offers the least resistance. For example, if 2 resistors $R_1$ and $R_2$ are connected in parallel and there is an incoming current $I$ then current is distributed as $$I_1 = I \frac{R_2}{R_1+R_2},$$ $$I_2 = I \frac{R_1}{R_1+R_2}$$ If you increase one of the resistance a larger ...


0

When the magnetic field is stationary and the coil is moving, the induced emf (called motional emf) is due to the magnetic field applying forces on moving charges within the coil, in accordance with the Lorentz force law $\vec{F}=q(\vec{E}+\vec{v}\times\vec{B})$. When the coil is stationary and the magnetic field is moving, the emf induced by the time-...


4

First off, energy storage doesn't really come into play in grid control. (Grid-scale energy storage is basically an experimental future technology that doesn't have a practical impact yet.) So the grid is basically about managing things such that supply=demand within very close tolerances. So: This is mostly done by throttling natural gas plants up and down,...


2

The generators have governors that control the speed of the machines. When generation exceeds load the machine speed up and the governor action slows back down (e.g. to 60Hz reference). In addition, many plants are on AGC which is a wide area approach to controlling frequency (and thus the generation-load balance). This reference should help and this also (...


0

An electron beam in a cathode ray can be deflected by a magnet, but the best way to deflect an arc would be to put a grounded conductor near-by. A near-by electromagnet would probably have the same effect (and don't hold it in your hand).


3

The transfer of charge ionizes the air around it, making that zap sound.


0

Overall a neutral dielectric can be seen as having a neutral charge distribution, but when you only have 2 opposite point charges, it does not work. The electric field produced by a dipole is Demonstration for the potential can be found here: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dipole.html We can check that this field satisfies what neutral ...


0

Between a negative and positive charged particle you have an electric field, an a dipole has both. Most el. fields start at one charge and end on another.


2

yes, the potential difference is the voltage.


2

Electric fields are conservative. Any shape you create with electrodes or insulators or dieletrics is irrelevant. A closed loop through any such static field will sum to zero potential change. So no current is created. Your field may in fact create a strong push on charges in the section between the electrodes, but the rest of the loop will feel the exact ...


0

If one charges an insulator, then yes, sometimes the excess charge stays on the insulator. A charged particle is attracted to any polarizable medium (static cling, in your socks, is this effect, writ large). Mobility of charge in such a situation is dependent on the LOCAL electric field, not the large-scale "it has multiple positive charges" ...


0

There are two main mechanisms which can be involved. For a discharge to occur, atoms in the air must become ionised. When the electrons and ions recombine, they release a characteristic energy which corresponds to a specific colour for that ion. This "corona discharge" can sometimes be quite faint and invisible in daylight, but if it is really not ...


0

It is possible to apply a force without having any motion (that should be obvious just from your day to day experiences, right?). So there is a repulsive force on the electrons but they don't move anywhere, at least nowhere fast because the force is not enough to push them through the insulator...at least until the insulator breaksdown. Like sticking a bunch ...


2

It is also the electric force, but caused by atoms/molecules of the insulating solid. Such an electric force is also found in conductors; the difference between conductors and insulators is in its implications on the mobility of charge carriers. And this is fully governed by quantum theory of solids: in short, in insulators an electron can not get into ...


0

So, for anyone interested I found the solution to my problem. I didn't know that there is a difference between voltage and "electromotive force". A short explanation can be found here: https://circuitglobe.com/difference-between-emf-and-voltage.html


-1

It is quite possible to have a net current of opposite direction in different locations of a wire. An example is a wire that reflects light under an angle. There will be a phase difference related to the angle, the wavelength and the distance between the locations, which can be an odd multiple of $\pi$.


3

Charge carriers can move arbitrarily, but current density is the net movement of all charge carriers at a given point. So current will only ever point in one direction at a time at any location. That current may represent the net movement of many individual charge carriers in different directions.


4

No, you cannot have multiple currents flowing in different directions in the same wire because all real wires have resistance. It will lead to inconsistencies with respect to other considerations, such as power dissipation. To illustrate, see the circuit below. Applying Kirchhoff's voltage law for the two loops solves for the two loop currents $I_1$ and $I_2$...


2

If you point your right hand thumb in the direction of positive current flow, your fingers will wrap around in the direction of the magnetic field.


1

If you apply alternating current to the terminals of coil the flux also changes direction and instantaneous flux also can be found by using right hand rule.


1

I think the problem arrives in the way the diagram on wikipedia shows the negative charges to sit on the wand and its metal sphere. While the large metal sphere is being positively charged, (actually it is having its negative charge stripped), these negative charged are carried by the belt towards the grounded earth, and thus 'disappear'. However once the ...


0

As it is rightly pointed out in an earlier answer that N and P layers offer a driving force for the carrier transport, I would like to bring a side advantage of these layers into the notice - The perovskites are prone to degradation by moisture. These N and P layers apart from rendering better charge extraction may also provide protection of the perovskite ...


2

[My] domes are all far from the VDG. In most design of VDG, I saw that one dome is placed encapsulating the top roller. But in my design, both domes are far apart connected with some cabling. That won't work. The fact that the upper dome encloses the apparatus that takes the charge off of the belt is the most important part of the design. It's literally ...


1

This answer is incomplete, as I'm no expert, but it may be of some help. The idea of having the top roller assembly surrounded by the dome is that the charges that build up on the outside of the dome will not give rise to an electric field inside the dome, so charges arriving on the belt are not inhibited from leaving via the top comb. I'm not at all sure ...


0

TV picture tubes and a CRO most CRO tubes, the phosphor on the screen and the inside of the tapered part of the tube are coated with aluminium, which is evaporated on. The electrons can pass through aluminium to the phosphor. Then they are then collected by the coating and returned through the EHT laed, which is clipped into a connector in the side of the ...


Top 50 recent answers are included