# Tag Info

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. ...

8

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 ...

4

I believe the question has been answered (earlier), but not explicitly. The question seems to be if an incandescent bulb requires 100 watts to produce 1690 lumens and an LED 23 watts to produce 1600 lumens, what is the theoretical minimum number of watts required to produce 1600 lumens. Using Jason and Sergei's answers (and Tom Murphy's paper already linked ...

33

Yes, there is a fundamental limit. It comes down to two factors: How many watts of light energy can the source produce for each watt of electrical energy? How many lumens does each watt of light energy correspond to? The first question is straightforward - by conservation of energy, 1W of electrical energy can yield at most 1W of light energy. The ...

6

Yes there is the thermodynamic law of Conservation of Energy. Light is a form of energy, and you can't get more energy out than is put into the system. This paper http://physics.ucsd.edu/~tmurphy/papers/lumens-per-watt.pdf puts the number at about 250 lm/W for "white" light

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

VA is used for apparent power and reactive power. Watt is used for active power. An inductor or a capacitor in an AC circuit does not dissipate energy, because the current and the voltage are 90° out of phase: energy flows into them during half the cycle, but it flows back during the next half cycle. The power lines have to supply that current however, and ...

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 ...

-1

You can reference these links: https://en.wikipedia.org/wiki/Volt-ampere https://en.wikipedia.org/wiki/Watt The prefex Kilo simply means 1000. So a Kw is 1000 watts and a KVA is 1000 volt-amperes. Hope this helps!

2

if there is a fan inside the tank and if the tank's volume is kept constant, what will be happen? The air will circulate and viscosity will convert kinetic energy to thermal energy, i.e. temperature will increase. The electrical energy input will be eventually converted to thermal energy which is $\delta Q$. So $W=pdV-Pt$ is not correct. The equations are, ...

3

The maximum and minimum are "local" values. As you move closer to A (at 0.2 m you are MUCH closer to A than to B) the amplitude of A is much larger - so although there may be destructive interference between A and B at that point, this is by no means perfect interference, and the resulting amplitude is still quite large (lot of A minus a little of B). ...

0

Apart from friction in the load (which cannot be predicted), the flywheel does not make any difference to the maximum rotation speed reached by the motor. If there is no friction, then given sufficient time the motor can accelerate the flywheel up to its own maximum unloaded speed, however small the torque supplied by the motor. An even higher speed can be ...

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 ...

2

So long as your electric generator is spinning then you will get electricity out of it The BIG problem with this construction is conservation of energy. You will have to supply energy to the windmill in order to get electric energy out of it. So to get an "infinite" amount of energy out of your windmill youd have to supply more than that to keep it ...

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