The time rate of change of energy

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1answer
325 views

Converting Langley to Watts

I'm reading a really old paper which looks at estimating the surface energy fluxes for The Great Lakes. They show all of their values as Langleys per day. Can this be converted to Watts per meter ...
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1answer
64 views

Power of several focused laser beams on a small surface

After viewing this: My Homemade 40W Laser Shotgun Will the initial 40W power of the diodes beams be roughly transferred to the targeted surface where the 8 beams are focused, or will there be a power ...
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1answer
54 views

can a power supply with high voltage value and some current be split into multiple small voltages of same current?

For example: if I have a source that can give an output of 10,000 Volts with some unknown current value, now, can i make that 10,000 Volts to 50 (need not be 50 exactly but maybe more than 30) of 200 ...
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0answers
82 views

How power spectral density in time domain can be understood?

I got some data which basically gives me the variation on the time of a PSD measured across specific frequency bands ranges, for instance [10Hz-30Hz]. However I have not found any good explanation ...
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1answer
282 views

Normalizing values in dB scale

I'm doing some experiments with optical power through a glass fiber. The power is measured in dBm. For the graphs that I make (Power in dBm vs time), I normalize the values relative to the initial ...
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1answer
286 views

Free Body for object on vertical wall, Applied force, Torque required for motion [closed]

I am trying to understand how to create a correct Free Body diagram and understand formula used to forces acting on object (i.e. a robot with 4 wheels) that is "placed" on vertical surface such as a ...
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2answers
72 views

Non-linear relationship between power supplied and perceived brightness in a filament lamp?

I was expecting the relationship between these two to be linear, but after conducting an experiment my data fits almost exactly on the curve, $y = 2800.2 x^{2.0173}$, where $y$ is the brightness in ...
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4answers
282 views

Ohmic Heating in Wires

please could someone tell me why Ohmic losses are always referred to as $I^2 R$ losses? Here is my problem. If the power coming from a power station is fixed then you can either deliver this power as ...
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4answers
605 views

What does it mean when we say that power of a bulb is 10 W? Since $V/I=$ resistance is a constant, how can power $=VI$ be a constant?

My question is simple. In Ideal situation, at constant temperature, we know that normal appliances like a filament bulb has straight Voltage vs Current graph, meaning its resistance is constant or ...
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1answer
115 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 ...
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1answer
81 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 ...
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0answers
38 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 ...
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2answers
184 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 ...
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3answers
153 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 ...
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1answer
314 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$\lambda$ = $(x/r)^2\phi$ where $\phi$ is the ...
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0answers
25 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
46 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 ...
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1answer
279 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 ...
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1answer
168 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 ...
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0answers
40 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 ...
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1answer
125 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) ...
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1answer
117 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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1answer
38 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 ...
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1answer
57 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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1answer
323 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 ...
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1answer
340 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 ...
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2answers
444 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 ...
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1answer
108 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 ...
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1answer
196 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 ...
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2answers
128 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 ...
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1answer
91 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 ...
3
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4answers
571 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 ...
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1answer
67 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 ...
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3answers
74 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. ...
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1answer
238 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 ...
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3answers
754 views

Laser power consumption vs power output [closed]

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?
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3answers
335 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?
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1answer
53 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 ...
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3answers
1k 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 ...
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1answer
120 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, ...
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2answers
699 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
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3answers
2k 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 ...
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1answer
56 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... ...
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1answer
86 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?
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2answers
47 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 ...
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1answer
52 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
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1answer
80 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 ...
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2answers
245 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 ...
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1answer
450 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
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1answer
69 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 ...