The time rate of change of energy

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1answer
2k views

Calculating the mechanical power of a water pump

Say I want to pump water from one container to another. The water levels are 3 meters apart, and I want to pump 10 litres per hour. I figure the mechanical power necessary, assuming no losses, is: $$ ...
1
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1answer
198 views

How to understand the thermal radiation?

I am studying the thermal radiation (Stefan–Boltzmann law) by myself $$P = \epsilon \sigma A T^4$$ here $\epsilon$ is the emissivity, $\sigma$ is Stefan-Boltzmann constant, $A$ is the surface area ...
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2answers
2k views

Light bulbs, Wattage meaning? [closed]

Light bulbs, Wattage meaning? Two incandescent bulbs (120 V, 25 Watt) and (120 V, 500 Watt) connected to the same batteries. Which one shines brighter? And why?
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2answers
290 views

How do you calculate power at the focal point of a mirror?

I'm a Mechanical Engineering student and I'm working on my senior project, so I need help. My project is about designing a solar dish having a diameter of 1.5 meters and a focal length of 60cm. so at ...
3
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2answers
2k views

Is it possible to get energy from electrical wire using induction?

Pardon me if this is a stupid question but my physics courses are from a long long time ago and I was a teenager back then. ;) Electricity in a wire generates electromagnetism, right? Would it be ...
0
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2answers
88 views

Nuclear based wireless power?

I would like to ask if there is any Nuclear process which can be used to produce a wireless power ? Is there any nuclear process can be radiate to the environment with no harm to human beings? ...
3
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1answer
2k views

Calculating displacement amplitude of ultrasonic power transducer

I am not a physicist, but my current project drives me to some physics-related computations, hence seeking help. I have some ultrasonic transducers, 5938D-25LBPZT, for which very limited information ...
7
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5answers
2k views

When driving uphill why can't I reach a velocity that I would have been able to maintain if I started with it?

Consider these two situations when driving on a long straight road uphill: Starting at a high velocity $v_h$, which the car is able to maintain. Starting at a lower velocity $v_l$, and then trying ...
2
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2answers
2k views

Harvesting electricity in the air from power lines:

Recently I came across this quote on the internet, about a person who apparently set up devices to extract electricity from the "air", on his own property: I read an article a couple of years ago ...
6
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2answers
2k views

Quantum Computing Power Advantages

Currently, the world's fastest supercomputer runs at 17.59 Petaflops, which consumes 9 megawatts of electricity. A qubit-based quantum computer has the potential to operate much more quickly for some ...
-1
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3answers
258 views

Power of a runner

How can someone calculate the power in watt that a runner produces, when he runs uphill and downhill? Is there any algorithm? It is important to take under consideration the uphill and downhill ...
0
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1answer
413 views

Is resistance to motion directly proportional to the speed of a moving object?

Power is known to be equal to the force x velocity (P=FV). Im solving a question that states the following : Car with engine working at 32 kW, mass of 1 tonne, travels at a constant speed of 40m/s ...
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2answers
622 views

Mechanics Question: Energy, Work and Power

I'm a pure mathematician by trade, and have been trying to teach myself A-level mechanics. (This is not homework, it is purely self-study.) I've been working through the exercises and have come up ...
0
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1answer
357 views

Mechanics Question: Work and Power

I'm a pure mathematician by trade, but have been teaching myself classical mechanics. I've got to the chapter on Work, Energy and Power and I've found an example that is causing me some problems. ...
2
votes
1answer
67 views

Sound intensity and space/things in the way

Suppose you have two stationary people, A and B, who are equally effective in terms of hearing ability, and A emits a sound that is heard by B at a certain intensity. If they remain stationary, and B ...
5
votes
2answers
605 views

Averaging decibels

Wikipedia: The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. If I ...
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2answers
8k views

Confusion about P=VI and V=IR

If we look at $P=VI$, we see that if the current doubles then the potential difference is halved but this doesn't seem to make sense according to $V=IR$. If we look at that equation, since the ...
2
votes
6answers
1k views

Confused about unit of kilowatt hours

So I am a little confused on how to deal with the Kilowatt hours unit of power, I have only ever used Kilowatts and I have to design a residential fuel cell used as a backup generator for one day. ...
2
votes
1answer
128 views

What are the properties and impediments of a liquid air fueled engine?

I recently came across a very interesting article that suggested the possibility of using liquified gases like air, nitrogen, or oxygen as a power source for cars. It appears that this company is ...
2
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2answers
217 views

Why do we need more power to do a job fast?

Let's assume we have two identical electric trains. One has a big electric motor (high power) and the other has small motor (low power). Let us assume the electric motors are of the same brand and ...
0
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1answer
3k views

Calculate the UPS Capacity in amp-hours [closed]

I am trying to find out the UPS capacity in amp-hours for my HP UPS system. I've already done some calculations based on the UPS information from the HP Power Manager software. Bellow are my ...
1
vote
2answers
697 views

An Ideal Transformer

In a transformer assumed to be transformer, power in the primary is equal to power in the secondary. So in a sense, the power in the secondary is 'fixed'. Output voltage in the secondary is also fixed ...
4
votes
4answers
3k views

Do resistor-based fan regulators save no power at all?

I have heard that the traditional resistor-based fan speed regulators are inefficient. In fact, I have noticed that such regulators tend to get hot when the fan is set to low speed. However, does that ...
0
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1answer
276 views

Power, Force Velocity

In any case, if the force and power is constant , does velocity also need to be constant? If no, can you tell me a case. Further can this be extended for non-rigid bodies.
3
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2answers
2k views

What is the luminosity per square meter hitting the Earth's surface from the Sun?

So I know that the Sun's luminosity is $3.839 \cdot 10^{26}$. What I want is the luminosity per square meter at the Earth's surface. So this is what I have got so far: I know the distance to the ...
10
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3answers
3k views

why aren't there nuclear powered aircraft?

I know this might sound like more of an engineering question that about physics, and it probably is, but bear with me: i'm still not sure if the answer to my question lies in the physics or in the ...
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3answers
5k views

Average power dissipated by a resistor on AC current

So let's say we have an AC current of 120 V at 60 Hz. Then i's waveform would be $$f(t) = 120 \sqrt{2} \cos(2 \pi 60 t)$$ Or rather the amplitude times $\sqrt{2}$ times $\cos(2 \pi ...
2
votes
1answer
409 views

Which speed can an electric scooter reach on a given slope?

Electric scooters are always "given" as "working with slopes up to xx%", but what does it mean? Given motor torque and power, scooter+driver weight and wheels diameter, how can I determine at which ...
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2answers
3k views

Does the 'mAh' rating of a battery have something to do with its power?

I'm curious about the 'mAh' of a battery: how can this impact the power of the battery? I've done some research on the internet, and most of the articles I found explain about the 'amount of charge ...
4
votes
4answers
7k views

How does power consumption vary with the processor frequency in a typical computer?

I am looking for an estimate on the relationship between the rate of increase of power usage as the frequency of the processor is increased. Any references to findings on this would be helpful.
2
votes
2answers
380 views

Should the term Watt's Law be used?

I'm revising some electrical curriculum for a technical training program. In the curriculum students have to calculate values using Ohm's law and the equation Power = Current * Voltage (or P = IV). ...
3
votes
2answers
207 views

Inefficiency Comparison of Car Air Conditioning vs. Open Windows

On a recent long, hot journey in Spain, I was pondering which was the most efficient way of cooling the car. Which of these would be the most effective? Switching on the air conditioning, thereby ...
0
votes
3answers
322 views

How to imagine the following power and torque?

I can roughly feel a force of 10 newton only by considering the weight of 1 kilogram object. How to imagine the following measurements? Maximum horsepower 16 hp @ 9,500 RPM Maximum torque ...
2
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2answers
202 views

Can wireless power transfer harm organic life by anyway?

Now, humanity can beam 50-60 watts power through 10 centimeter-thick concrete block. Can such wireless power transfer harm us by anyways?
2
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2answers
381 views

Lorentz engine to run a car?

Could a Lorentz engine (like the ones that move the write head inside of hardrives) be used to run car ? Would it be possable to get it producing 60hp, and a decent amount of tourque, if so how large ...
0
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1answer
122 views

Do you think it’s possible to make a power plant of the described kind?

We are working on a science project and try to engineer a power plant of a new kind. It is called Air HES (air hydroelectric station). The idea is described on our website. Do you think it is ...
1
vote
3answers
5k views

Two 60W-lightbulbs are connected on 220 V AC-voltage - how much electric power is spent by each lightbulb? [closed]

Two 60W-lightbulbs are connected on 220 V AC-voltage - how much electric power is spent by each lightbulb? There are two scenarios: In one, these two lighbulbs are connected serially, and in the ...
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2answers
425 views

Calculate power $P=V \times I$

I have an adapter which mentions like this... Input: 100-240V~1.8A 50-60hZ So how much power does it really consume? I just knew ...
2
votes
1answer
1k views

How are the CPU power and temperature caculated/estimated?

From Wikipedia The power consumed by a CPU, is approximately proportional to CPU frequency, and to the square of the CPU voltage: $$ P = C V^2 f $$ (where C is capacitance, f is ...
3
votes
1answer
9k views

Is there any significance to 1.21 GW?

In connection with a related question on Science Fiction & Fantasy Stack Exchange page: does this number 1.21 GW make any sense? What is 1.21 GWatts? With what can you compare it? Can the ...
1
vote
1answer
74 views

is it possible to gain from charging cold battery

Is it possible to get higher load of energy into a battery if you charge it when its cold eg. +9C? the battery is emptier, but does it let the power in? Is it safe?
3
votes
1answer
127 views

What are some ways that humans could have influence over what sequence a star was in?

How would a society go about either preventing our sun in its primary sequence from going into a Red Giant a billion years from now? Or perhaps, accelerating the process of going from main sequence ...
2
votes
1answer
77 views

Boiling water reactor

What are the typical power densities in conventional boiling water nuclear reactor per cubic centimeter of fission material?
2
votes
1answer
1k views

Finding electric power generated using heat transfer

I'm working through an example I have been given to study. Suppose I have a 2m X 4m photovoltaic panel on my roof that is irradiated with a solar flux of $G_s = 700W/m^2$. Given: $\alpha_s = 0.83$ ...
2
votes
4answers
431 views

Should we forget fusion and focus on geothermal power? [closed]

Firstly I can say that I would love us to come up with a sustainable fusion solution. However with the latest estimates being 2050 at the earliest for an effective fusion solution and the planets ...
4
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1answer
42 views

Have Sterling Engines Been Used In Outer Space?

I was reading about Stirling Generators having potential applications for power generation in outer space. Have Stirling engines ever been sent into space?
3
votes
3answers
889 views

Would a thinner atmosphere (such as high altitude) yield better solar panel energy generation?

I am curious. If you were to put a solar panel up in high altitude or on the surface of the moon, both of which have much less atmosphere to reflect/refract light, would that solar panel produce more ...
39
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8answers
14k views

What practical issues remain for the adoption of Thorium reactors?

From what I've read on thorium reactors, there's enormous benefit to them. Their fuel is abundant enough to power human civilization for centuries, their fission products are relatively short-lived, ...
3
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1answer
231 views

Lifetime of battery

If I directly connect two terminals of 3V battery (negative to positive) using copper wire, would it lose all its charge faster compared to another 3V battery that is used to lighten a 1.5V bulb?
3
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1answer
137 views

Can a solar thermal collector designed for use in homes ever power a stirling engine designed for use in homes?

Can a solar thermal collector common on private roofs today designed for collecting heat for the household ever collect enough heat to power a stirling engine of say this model: ...