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44 votes
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How does a transistor act as an amplifier considering energy conservation?

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

Why can I use P = I²R but not P=V²/R when calculating energy lost in a circuit?

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 ...
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33 votes
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Why can I use P = I²R but not P=V²/R when calculating energy lost in a circuit?

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

What is the speed of "electricity"?

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 ...
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24 votes
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Heat lost in ideal capacitor charging

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} +\...
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24 votes

How many watts does a 40 MHz radio frequency signal create?

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 ...
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21 votes
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Where does all the inductor stored energy go?

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{\...
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  • 55.5k
20 votes

What is the speed of "electricity"?

(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 ...
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18 votes
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Why don't we think about battery storage for all sources of electricity on a utility scale instead of just renewables?

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 ...
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18 votes

Why don't we think about battery storage for all sources of electricity on a utility scale instead of just renewables?

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 ...
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18 votes
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Why is the energy in a battery QV, but the energy in a capacitor QV/2

Short answer: an ideal battery has constant voltage \$U_{nom}\$ (nominal voltage) until it's empty, so energy stored is: \begin{aligned} E &= U_{nom} \times I \times T\\ &= U_{nom} \times \...
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17 votes
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Why is home voltage value higher during the night?

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 ...
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16 votes

Is a microwave's output power proportional to the mass of its contents?

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 ...
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  • 160k
16 votes

How can I deduce the power of a capacitor from its datasheet?

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 ...
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15 votes
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Will repeatedly turning a light bulb on and off damage it?

It depends on the type of lightbulb! Halogen, incandescent, fluorescent, and vapor lights all use tungsten filaments that heat up and emit electrons via thermionic emission. In that sense, they are ...
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14 votes

Does an EEPROM consume power only during the transition edges or during entire read/write cycle?

Here is an example write current waveform from the NXH5104 4 Mbit Serial SPI EEPROM datasheet. In the table of 'Static characteristics' the average write supply current with 4 sectors active and 5 ...
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13 votes

How does a transistor act as an amplifier considering energy conservation?

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 ...
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13 votes

Heat lost in ideal capacitor charging

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 ...
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  • 385k
13 votes

What is the speed of "electricity"?

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 ...
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13 votes
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How to shunt 1500 joules when voltage exceeds 75 VDC

It seems perfectly feasible to dump the load into a 1 kW wirewound resistor using a mosfet. Example resistor: Vishay p/n FSE100022ER500KE This is a 1 kW wirewound resistor rated for 10x overload for 5 ...
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  • 24.4k
12 votes

Electrical energy in a fighter aircraft

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 ...
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12 votes

What's the most economical way to digitally measure 240V mains voltage, current and power factor?

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 ...
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  • 385k
12 votes

What if we attach a TEG between a freezer and stove?

It works, but the way in which a TEG works is to extract energy from the flow of heat like a waterwheel extracts energy from the flow of water. So you'd be cooling the stove, and dumping heat into the ...
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  • 45k
11 votes

Producers consumers balance in the grid

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 ...
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  • 16.1k
11 votes

What is the speed of "electricity"?

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,...
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11 votes
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Intuitive way of "visualizing" how the energy is stored in an inductor?

I'm going to start by discussing capacitors then move to inductors. I'll avoid complex equations (to save myself as well as this discussion.) I may even discuss duals between capacitance and ...
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10 votes

In the USA, the grid transmits power at/around 60Hz. How big of a frequency deviation can the grid handle before relays trip and cause a blackout?

Short answer: The range is usually held within ±0.5%, so its from 59.7Hz to 60.3Hz for a 60Hz grid. Long answer: Frequency is regulated tightly because it's how the overall load in the grid is ...
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10 votes

Relationship between I2C drawn energy / power consumption and data rate

The I2C data and clock lines draw power when they get pulled low. Because then power is sunk through the pull-up resistors. While a line is pulled low it will draw 5V/4.7k\$~\Omega \approx\$ 1mA. ...
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10 votes

Why don't we think about battery storage for all sources of electricity on a utility scale instead of just renewables?

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 ...
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