Hot answers tagged

44

The base current in a transistor controls the collector current. The energy comes from the power supply. It is not generated within the transistor.


36

The problem assumes you understand something that is not clearly spelled out: the wires and the (unknown) load are in series. Therefore they share the current, not the voltage of the battery. That's the situation: simulate this circuit – Schematic created using CircuitLab As other have pointed out, the voltage drop across the wires is small given ...


33

60A through a 0.01ohm resistance gives a 600mV drop. That is the voltage you need to use in the equation.


29

For most of the copper wire and traces you see, about 60% the speed of light in a vacuum. The energy is the signal so they are the same. The speed of electrons is much slower...slower than walking pace. The electrons aren't moving to and from the powerplant 60 times per second. Think the difference between the speed of sound and the wind. The wave (energy) ...


25

The field strength at a distance from the inductor is critically important. If the inductor is well shielded, with zero field in the space nearby, then it won't act like an antenna. Obviously. So, how can we maximize an inductor's distant field and create a good radio antenna? Well, first we should wonder about the distance involved. The field must be ...


24

The problem with these theoretical examples lies in the fact the current is assumed infinite for 0 seconds. Crudely substituting this in the conservation law: $$ \frac {\partial \rho }{\partial t} +\nabla \cdot \mathbf {J} = 0 $$ $$ \frac { \rho }{ 0 }+ \infty \neq 0 $$ Since charge is conserved, the assumption of infinite current in zero time is wrong. ...


24

This is like asking "how bright is a red light?". It's as bright as it is. You can make a bright red light or a dim red light. As another answer points out, the energy per photon of an electromagnetic signal depends on the frequency of the signal. But you can make a brighter or dimmer (higher or lower power) source at any frequency by emitting more or fewer ...


23

Indeed it can be a very good antenna. Look no further than the transistor radios and AM band receivers. In those ubiquitous consumer goods the antenna consisted of a piece of very low loss ferrite with a very high permittivity. This was wrapped in many amp*turns of very fine copper wire. The high permittivity gave the antennas an effective cross-...


21

If i remove both terminals rapidly enough to avoid any arc formation The more rapidly you remove the terminals, the more an arc will want to form. Ideal inductance is defined by: $$ v(t)= L\frac{\mathrm di}{\mathrm dt} $$ If you remove the terminals "instantly", then the current must stop "instantly". That means the di/dt term will approach infinity, and ...


20

(added) The wave speed ratio of electricity v/c is limited by the relative permetivvity, \$ε_r\$ of insulation around the conductor for the speed, v relative to speed of light, c in a vacuum. It is also limited by the relative magnetic permeability, \$\mu _r\$ in the wire or closely coupled around it, as this would occur in magnetic components. \$v/c = 1/\...


18

This is mostly a con. The circuit is probably only to light the LED so that it looks like it's doing something. Most power grid loads, like your house, are inductive. Inductive power factor (current lagging voltage) can be offset by adding capacitive power factor (current leading voltage). If you get it just right, then the result looks resistive, which ...


18

Taking, at random, Overland Park, Kansas, as an example: Population 191,278 (2017). Area 195 km2. Annual energy demand (per capita) 13,500 kWh = 37 kWh/day. World Bank. City demand = 191278 x 37 = 7 x 106 kWh/day = 7 x 109 Wh/day = 3600 x 7 x 109 = 25.5 TJ/day. For pumped storage the formula for energy stored is \$ E = mg\Delta h \$. Assuming we could ...


18

I am not sure exactly what you are expecting as an answer, but storage has already started to be used to supplement all energy sources. Utility-connected battery banks have already proved superior to any alternative peaker plant. This report on the Australian 129MWh Tesla battery installation's first year of operation could shed some light on it. In just ...


17

TL,DR; What you are seeing is primarily the result of reactive load droop sharing, with secondary loading voltage drops in the transformers and lines. When generators run in parallel like they do to supply national grids, there are two mechanisms at play that largely go unnoticed by the local population. Perhaps the most critical one is speed droop load ...


16

Simple thought or practical experiment: If he's right then the heating time to bring water to boiling point is independent of the quantity of water. One cup will take as long as two. If you're right two cups of water will take twice as long to boil.


16

Capacitors don't have power ratings because, ideally, they don't dissipate any power. They store energy unlike resistors which consume energy, giving it off as heat. Instead, you need to consider the following: The voltage rating needs to be at least that of the maximum voltage they will see in service. For power regulation and loudspeaker connection ...


13

It depends on the type of lightbulb! Halogen, incandescent, florescent, and vapor lights all use tungsten filaments that heat up and emit electrons via thermionic emission. In that sense, they are similar. However, the method to "turn on" the lights varies. Incandescent bulbs are simply turned on once and left on. The inrush current is on the order of 12 ...


13

The 'catch' is that a transistor only controls the flow of current; it does not itself generate power. The power would come from some other part of the circuit, perhaps from the electric company via a power supply or from a battery. Now, one possible point of confusion is that transistors can be represented as equivalent circuits that contain a so-called ...


13

When masses collide in an inelastic manner, momentum is conserved but energy has to be lost. It's the same with the two-capacitor paradox; charge is always conserved but, energy is lost in heat and EM waves. Our schematic model of the simple circuit isn't sufficient to show the subtler mechanisms at play such as interconnection resistance. An elastic ...


13

You need to separate two slightly different concepts. There is the electron drift velocity which is the speed at which the charge carriers in the wire move due to the electric field (and is basically negligible, think mm/s) and the propagation velocity of the EM wave between the conductors which is a significant fraction of lightspeed. It is the em wave ...


12

It's conceptually similar to an automotive electrical system. There is a generator (driven by the engine), batteries and some other stuff. Small planes tend to use 28VDC for the power bus, which is just double the voltage used in an automotive electrical system (voltage is quoted with the fan up front running, since there will be bigger problems should it ...


12

I used to design electricity meters so I'm biased. There's only one way to measure power (digitally) and that is to simultaneously sample the voltage and current waveforms at a reasonably high rate such as 1kSps or above. You multiply the v and i samples to get instantaneous power samples. You then average these power samples to get true average power i.e. ...


11

When you make a traditional inductor, you are trying to minimize the leakage inductance. In so doing, you try to get as much of the magnetic field to cut through nearby turns of wire. A toroidal inductor is particularly good at keeping its field to itself. The "leakage" part is that which radiates away into space, without being captured by the coil. ...


11

Grid frequency is where the magic hides.... There is energy storage in the inertia of all that spinning steel, and more the other side of those throttle valves in the PE of hot water trying to be steam. The grid frequency is really the integral of the difference between generation and load divided by the total mass moment of inertia in the system. $$\...


11

Apart from the actual electric grid part of the question, I think you might have a confusion about the speed of electrons and the drift velocity. What I'm saying is, when you say speed of electricity, I think you mean the speed of current, which is pretty fast, or the speed of electrons, which is also pretty fast, or the drift, which is pretty slow. (Pretty ...


10

Part of your basic premise is false: gas turbines can go from zero to full power in a matter of minutes. They've been used to provide peaking power for decades, since it's rare for power demand to vary so rapidly that they can't handle it. Because traditional generation capacity can be changed so quickly, there's no need to store electricity on more than a ...


9

In the CPU it's all heat. It's the changing from 0 to 1 and back (which ultimately is what a computer does) which consumes the energy, because charge has to be moved from one place to another, and it's this current (moving charge) through resistance which causes heat. \$P = I^2 \times R\$ Ideally a computer which doesn't perform any tasks consumes no energy,...


9

I am wondering if the energy loss in a voltage drop over an entire circuit is equal to the energy transferred from the circuit (e.g. light/sound/mechanical energy/heat). Yes. Energy is conserved. Any electrical energy that is lost by the circuit is transformed into some other kind of energy. It is often heat, for example in a resistor or a diode. It could ...


8

You are confusing kilowatt hours with kilowatts per hour (which is a fairly useless measure of anything). A kilowatt is a measure of the rate at which energy is delivered (also known as power). One kilowatt means that 1000 joules of energy is being delivered every second. A kilowatt hour is a measure of total energy delivered. kilowatt = energy/time ...


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