# Tagged Questions

The time rate of change of energy

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### Average Power and Instantaneous Power

I am confused between the usage of the terms average power and instantaneous power. What is the main difference between the two?
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### Could a civilisation contact us by laser from 50 light years away?

The Kepler Space Mission has discovered over 1,000 planets. These discoveries may increase the confidence of some people that other civilisations exist. That is an opinion issue, and not what I want ...
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### Why are GPS transmitting signals made so weak?

Twice this year, my car's GPS receiver got totally lost. It seemed the cause of this was heavy cloud, (because I can't think of any other reason), and the GPS stayed in "Recalculating" mode, until ...
117 views

### Does a switched on power socket consume electricity? [closed]

Lets say I have a TV and a power socket but the TV switch is off however the socket switch is switched on, so will it consume electricity?
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### Formula connecting Force and Power

Is there such formula? There probably is of course, but i would like a very concise description of how to derive it, in order to better understand myself. Thank you in advance.
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### Work done by flow of a fluid

I'm looking at the power a flow of steam in a turbine. I originally assumed that the kinetic energy of a moving section of steam was equal to (let $V$ be volume, $\rho$ be density, and $v$ be velocity ...
282 views

### relationship between voltage and current

I know that this question had been asked many times but I think it will be a new info in Ohm’s law: $$R = V/I$$ So Voltage is directly proportional to Current In Electric Power’s law: $$P = VI$$...
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### General relation between power density of any engine and dissiapation rate and temperature

Many years ago ( before my university studies ) I read that renewable resources are fundamentally limited by laws of thermodynamics to produce energy very slowly (low specific power or power density) ...
139 views

### What does 400kW(e) mean?

I am trying to read a document and it says a power grid is 400kW(e) what does this mean?
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### How much power does it take to keep a massive particle suspended in a gravitational field?

For instance if I have a rocket of mass $m$ in a uniform gravitational field $g$, and I want to keep it floating in the air via thrust alone, then how much power in the form of (say) chemical energy ...
58 views

### Energy consumption on resistance in AC circuit?

The electrical part of a PM machine is described as a symmetric three-phase Y-connected circuit with floating neutral point, $e=Ldi/dt+Ri+v$, where $e$, $i$ and $v$ are vectors of emf, current and ...
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### Maximum power transfer proof

I have the following homework problem. Consider a power supply with fixed emf $ε$ and internal resistance $r$ causing current in a load resistance $R$. In this problem, $R$ is fixed and $r$ is a ...