The time rate of change of energy

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2answers
45 views

Speed to power conversion

Here it is stated that there is a cubic relationship between fan speed and power consumption (Pfan ∝ FanSpeed^3). I have the fan speed (m/s), but I need to convert it into power (W). How can I compute ...
-1
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0answers
31 views

Power output of a galaxy problem [on hold]

A galaxy contains 10^9 M⊙ of neutral hydrogen. Given the transition rate for the hyperfine transition is 2.85*(10^-15) s^-1, calculate the galaxy’s power output (in W) in the 21-cm line. How ...
-1
votes
0answers
13 views

What motor is required to run lift 200 kg on 25 feet? [closed]

I am working on a Lift project for a wheel-chair , & i am wondering what power of motor and pulley is required for 200 kg , 1 person lift.
-3
votes
0answers
15 views

What is the Power delivered by the elevator motor [closed]

A motor which drives an elevator operates at an efficiency of 85%. The motor must overcome a frictional force which is 15% of the weight of the elevator and passengers. If the elevator has a mass of ...
0
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0answers
10 views

Circuit providing output? [migrated]

What does it mean for a circuit to provide an output power of say 1000W? Is "circuit providing power" referring to the battery supplying energy to the external circuit, or is it referring to the power ...
4
votes
1answer
55 views

Passively moving air [closed]

I'm interested in channeling air into an underground condenser to generate water. Which of these approaches would be most appropriate, and is there a better approach I haven't considered? A: A ...
0
votes
0answers
14 views

electromagnetic losses at conductor interface at high frequencies??

Skin depth effect reminder When an electromagnetic wave arrives at a conductor interface of conductivity $\sigma$ , most of it is reflected back. Only a small fraction penetrates as an evanescent ...
1
vote
0answers
28 views

How does the optimal-gear indicator work? [migrated]

Modern cars like BMW, Ford, Audi come with a system on the panel which tells the driver the next optimal gear to drive. How does it work ? What is the algorithm behind it? What data does it require ...
0
votes
2answers
33 views

Calculate required power output for a laser

How to calculate power rating required for a laser in order to produce a dot at a specific distance after reflection? For example, the laser is 10cm from the mirror, at an angel of 30 degrees it ...
0
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3answers
46 views

How does $p=fv$ hold when $v=0$ and an engine is working?

Standard high school equations: Work = Force x Distance Power = Work / Time = Force x Distance / Time = Force x Velocity When a space rocket takes ...
1
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0answers
64 views

Flux Linkage Inside of a Conductor

Can someone explain to me why the flux linkage inside of a conductor is dependent on the cross sectional area of the conductor? My book says that d$\lambda$ = $\frac{x^2}{r^2}$$\phi$. Where $\phi$ ...
0
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1answer
28 views

Ratio of two RMS values in recorded audio

A quick(ish) question: I produce music and I am having a discussion on the difference between two RMS values in a specific record Nero: The Thrill (Porter Robinson Remix). In the verse, the RMS is ...
0
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0answers
16 views

How does one measure the power factor?

How does one measure the power factor? $$\text{power factor}\equiv\frac{\text{power}}{|V||I|}=\frac{R}{\sqrt{R^2+(1/\omega^2C^2)}}$$ for an RC circuit driven with $V(t)=V_0\cos{(\omega t)}$.
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2answers
39 views

Simple Circuits [closed]

I have a small and easy dilemma, judging by how sophisticated the website is, and need a simple answer for it So $P=E/t$. And $P=I*V$. Therefore $E/t=I*V$. I just need an explanation on how this is ...
0
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0answers
22 views

High resistance wire as a heating element

I'm redesigning one of the labs for our senior lab class at my university. It's a thermal conductivity experiment meant to measure aluminum's thermal conductivity in a thin (1.1 cm diameter) rod. I ...
0
votes
1answer
83 views

Find the electric field of light due to an LED [closed]

This is a JEE mains question which neither me, nor any of my teachers can figure out. Help me here. "A red LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the ...
0
votes
1answer
37 views

Power dissipation across resistors in series

Suppose we have a simple circuit with an input voltage source $V$ and two resistors. Now if we want to find the power dissipated by each resistor using the formula $V^2/R$, should the voltage be the ...
1
vote
0answers
25 views

Calculating power in fluid systems with $pQ.$

I was wondering: say we have a fan which is being used to provide lift to some mass, like in a simple air cushion device, where the air has to flow through a chamber beneath the fan. Let's say that ...
0
votes
1answer
23 views

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) ...
0
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1answer
57 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?
1
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1answer
28 views

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 ...
0
votes
1answer
45 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 ...
1
vote
1answer
87 views

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 ...
0
votes
1answer
80 views

Car Motion: Power and Distance: Air Drag [closed]

I need to workout the amount of Power required by a car, in order to overcome air drag forces. I have figured out that, Power = c(Velocity^3). But, I am unable to understand Power's relation with ...
1
vote
2answers
273 views

Human Muscle Energy - Increases or Decreases by doing work?

When Human does some work, he gets tired. I will think he looses some energy. If he really loses energy by doing work how does he gain more strength to do more work later. His muscles become strong ...
5
votes
1answer
44 views

Does ambient day/night temperature change have significant energy generation potential

Is there significant energy to capture in daily day/night temperature change? For instance, I see from posts such as the following that there are materials with varying coefficients of linear thermal ...
0
votes
1answer
44 views

Negative power measurement of transformer short-circuit test. What happened?

I have a dissectible transformer, made up of two 120-turn coils. I connect a function generator to the primary side, set the AC voltage to be constantly 10V, and short circuit the secondary side. And ...
1
vote
2answers
54 views

Instead of a dynamo-meter, why can't we use $\tau=I\alpha$ to determine the power of a rotating shaft?

To measuring the power of a rotating shaft, dynamo-meters are used. Instead, why can't we find torque using Torque=Moment of Inertia times Angular Acceleration, $\tau=I\alpha$? And given that we know ...
0
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0answers
26 views

Non-linearity of energy conversion efficiency

I have a very general question to all of you. I am wondering if there is any basic physics principle that would state that energy conversion efficiency will be always non-linear (for the practical ...
-1
votes
1answer
53 views

What is one human power? [closed]

some time ago I was asked what the HP equivalent of a human was, looking into this apart from in the creation of steam engines the power definition 1 Horse power was set at the work of two of the best ...
2
votes
3answers
318 views

Car “oomph”: power or torque?

Two of the most important magnitudes that characterize a car's engine are maximum power and maximum torque. How are those two magnitudes related to the sensation that the car has "oomph" or is ...
0
votes
1answer
49 views

Electricity from effervescence, is it possible?

I've had this idea for quite some time (after having a cold and seeing Tabcin sparkling tablets), is there the possibility to generate electricity from effervescence? I envisioned something like the ...
2
votes
3answers
49 views

Solar plants and energy conservation

I'd like to apologise if this question is stupid or if it was asked ten thousand times - I haven't found an answer to it. Quite possibly due to mediocre English or abominable knowledge of physics. ...
0
votes
1answer
108 views

Can we make a “Gravity Mill” based on principle(s) of Newton's cradle?

DISCLAIMER: Newbie/Wannabe Physicist. What's to stop us from making a "Gravity Mill" which is a bar/rod attached with weights on both ends and pivoted at the ...
1
vote
2answers
99 views

Laser power consumption vs power output

I have a 5 mW laser pen powered by a 1000 mAh 3.7 volt battery that takes over 2 hours to recharge. It drains it in 15 minutes. Why is it only called 5 milliwatts output if it is consuming 14.8 W?
0
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3answers
53 views

Electricity consumption in fan

Does regulation in a fan vary in Electricity consumption? i.e. I want to know exactly, is the energy consumption more when regulator is tuned to highest number or lowest number?
1
vote
1answer
43 views

Is it true that a processor with a higher temperature uses inevitably more power in comparison with a processor with a lower temperature?

If a processor has a higher temperature, can you be sure it it consumes more power than a processor with a lower temperature? And is the reverse relationship true? A processorchip with a higher mean ...
1
vote
3answers
277 views

Defining Reference Directions for Voltage and Power (sign convention)

My professor decided to use the above reference directions when calculating power in circuits. He says that when power > 0, power is consumed. When p < 0, power is generated. This definition is ...
0
votes
1answer
60 views

Why aren't (domestic) kettles insulated?

In my experience of buying and using kettles, I have come across none which are insulated. The obvious reasons as to why it would be beneficial being that heating time would be reduced, similarly, ...
0
votes
2answers
111 views

What's the intensity of a laser pointer?

The unit of intensity or the irradiance of the light is $\mathrm{W/m^2}$. So what's the intensity of a light pointer? Searching on the web, the laser pointer's power is about $5\mathrm{mW}$, imagine ...
4
votes
3answers
1k views

What does 1714 mean in hydraulics?

After reading this answer: http://www.answers.com/Q/What_does_1714_mean_in_hydraulics, I still do not have a good idea of what 1714 represents. In fact, in the equasions I was working with I saw a ...
0
votes
1answer
46 views

What is the equivalent of the “amount of fuel” for a battery?

I am trying to make a performance diagram of an electrical powered device vs range, speed, etc. I want to compare it using the equivalent of fuel for a battery? I am not sure if it is just voltage... ...
-1
votes
1answer
43 views

Energy stored in hard disk [closed]

What is the type of energy stored in hard disk when data is stored? And Can we use it for electric power production?
-5
votes
1answer
57 views

What is a watt? [closed]

So in class I have learned that a watt is volt * amperre. In America they have 120 volts in the switch, while in Europe we have 220-240. I have seen the same powersupplies in the Us and the Eu, which ...
0
votes
2answers
34 views

Does the effect change if a continuing and constant force acts upon a mass?

If a continuing and constant force $F$ acts upon a body with the mass $m$, does the power (work per unit time) increase over time? It would mean that the converted energy per time unit increases. Is ...
0
votes
1answer
39 views

Too many antennas around a single energy transmitting antenna?

I am not a physicist. So I am not even sure, if I am phrasing this question properly. Lets say there is a wireless transmitter transmitting energy. Let us say I place $N$ number of antennas around it ...
1
vote
1answer
66 views

How big would a Dyson swarm have to be to supply the whole earth's human population with power?

If human energy consumption per year is 150,000 Terrawatt-hours, and the energy output of the sun is about 380 Yottawatts, how much area would you need at a distance of 0.5 Astronomical unit, in order ...
0
votes
2answers
99 views

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second?

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second? Not exactly a physics question per say, but it falls in the realm. How do I convert/understand ...
0
votes
1answer
180 views

Calculating estimated HP from velocity, auto weight, and constant acceleration

I am working on a simulation program that runs theoretical performances of different cars and was wondering if there is a way to estimate the HP at any running RPM? the problem is (and this may be me ...
0
votes
1answer
47 views

Out of phase AC transmission lines in parallel

I've been reading up on power transmission networks and came across this thing. http://en.wikipedia.org/wiki/Quadrature_booster Basically it balances the load between two parallel power lines by ...