The time rate of change of energy

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Which power equation to use: $P = I^2 * R$ or $P = V^2 / R$?

Given are ideal max voltage $V = 200\;\mathrm{V}$ and max current $I = 5\;\mathrm{A}$. Therefore: ideal resistance is $$R = \frac VI = \frac{200 \;\mathrm{V}}{5\;\mathrm{A}} = 40 \;\mathrm{\Omega}$$...
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2answers
37 views

Can an Oven being set to a different temperature cause electric board to go off?

Basically: the electrical system kept going off (when light goes down in a division due to too many electrical appliances on at a time, or their combined power consumption). My roommate said it was ...
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1answer
1k views

Total power consumption of electric device

For some electric devices, like a fan or air conditioner, I read about their power consumption in watts on their specification guide. Does it tell about the power at normal or full speed? or Does the ...
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1answer
23 views

How can the amplitude of the same acoustic wave be different in a interferometer?

I came up with an exercise on Halliday Resnick Krane that asked a question which consfuses me. I premit that I do not look for a solution of the exercise but for suggestions only regarding the ...
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1answer
37 views

Understanding the energy transffered/used from a power source?

A source of power(from a generator,battery,etc...) is used to power a system of any kind. We can calculate the energy used via this formula $E$ = $IV$ x $t$ ? For example, a battery that is connected ...
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1answer
30 views

Energy dissipation in current flow

In section 4.8, Energy dissipation in current flow, of Purcell and Morin's Electricity in Magnetism, the expression for the power expended by a resistor is derived. The sections includes the following ...
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1answer
21 views

Do we use rms values or peak value for calculating power of a transformer?

Do we use rms values or peak value for calculating power of a transformer? I have an A levels exam tomorrow and I wasn't able to find any kind of explanation in the book.
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40 views

What exactly is average power?

This question arises due to a problem I'd been solving recently: The question was to find the average power supplied by the water over the six hour period. Now I have read this post which ...
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1answer
128 views

Intensity of a standing sound wave at displacement nodes?

We know $$P = F\cdot v$$ where $v$ is the velocity vector. Since at the "displacement nodes" in a standing sound wave the velocity of the particles is always 0, the Power must be 0 and hence the ...
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1answer
64 views

Calculate spectral radiance at defined wavelength given radiant power

I am struggling with what I think is actually a simple problem. I have an LED that emits infrared light (950 nm). It is part of a sensor system. The manufacturer claims it has a radiant power of 3000 ...
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1answer
162 views

Nuclear to Electricity Energy Conversion

Currently nuclear power generates heat, which heats water into steam that turns conventional turbines. The energy conversion is as follows: photonic->heat->kinetic->electric This would result in low ...
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1answer
61 views

How much power is needed to drive two times faster?

Suppose a cyclist riding at speed $v$ decides to accelerate to speed $2v$. Does she have to generate $8$ times more power to sustain that speed? $P_1=F_dv$ If we double the speed, (it usually ...
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1answer
199 views

Power output of electrical hotplate

This sounds simple but i need some clarifications. I am using a hot plate to heat a solution in an oil bath. The power rating and maximum temperature of the hot plate is 1520 W and 500 oC ...
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1answer
27 views

Why does power loss in pure metal caused by temperature is calculated base on $P=I^2R$ but not $\frac{U^2}{R}$

$$P=I^2R=\frac{U^2}{R}$$ The metal's resistivity is temperature dependent, neglect the change in size by temperature. The power loss of a pure metal when it drop form temperature $T_1$ to $T_2$ is $$...
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1answer
50 views

Does the power of the resistor change when the battery is changed?

Wanted to know whether the changing of a battery (potential difference)affects the change of power consumption of a resistor of a bulb. please tell me how the change will occur?
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1answer
58 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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1answer
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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1answer
69 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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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
53 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 ...
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1answer
44 views

How can power factor be improved by using a capacitor in an LCR circuit?

First of all what is even meant by improving power factor? My book says we can improve power factor by making impedance tend to resistance I.e. Z-》R, and then they say that power factor is improved by ...
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0answers
40 views

Geometric frustration in power transmission networks

I read this article concerning the detection of Braess Paradox on power transmission networks: http://phys.org/news/2012-10-power-grid-blackouts-braess-paradox.html Here is a quote from the article: ...
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0answers
199 views

How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
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0answers
32 views

Estimating the battery capacity using current power consumption and battery percentage

I want to estimate the current maximum capacity (in kWh) having the current power consumption (in kWh) and the state of charge of the battery (in %) available in a time series. I do not have a full ...
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0answers
32 views

How to apply conservation of energy to active noise-cancelling headphones?

Active noise-cancelling headphones add the opposite waveforms of the ambient sound in order to cancel out this ambient sound by destructive interference. I do not understand why adding more power in ...
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0answers
47 views

Voltage and reactive power

Why are reactive power and voltage related? When the control system of a generator increases/decreases the current of the rotor, voltage and reactive power are increased/decreased.What is the relation ...
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0answers
39 views

Sound frequency and power

Although I have studied physics I am not clear on this question: Given that two (or more) sound waves have the same amplitude does the power they carry depend on frequency? What about electrical AC ...
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0answers
17 views

Power of solar panel and dc generator

I have made a solar stirling engine and I need to measure its power and compare it to the output power of a solar panel. I need to see which one is more efficient. I am using the same area in both ...
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0answers
73 views

Luminous intensity: from Volt to Candela/m2

I use a probe for converting optical power to an electrical current. I need to convert Volt to candela/m2. The sensor, a photodiode, measure the brightness of the monitor leaning the probe on 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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0answers
104 views

What is DX technology and what are the effects on digital cameras?

I am photographing in a high power voltage field in Industry producing aluminium, called DX technology. How do I know if my digital camera will not be affected? At 350kA current my film cameras were ...
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0answers
201 views

Max speed as a function of engine power

My question started out as finding the maximum speed of a go kart, taking into account only the drag forces as force opposing the motor. I've done some investigation to find: $$ F_{drag}=\; \frac{\...
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0answers
44 views

Energy stored in a battery?

I want to calculate the energy lost from a battery to heat, and the energy stored in a battery. Are these formula's correct? $ E_b$ = $I$$V$ x $t$ $ E_H$ = $I$$R$$^2$ x $t$ $E_b$ = energy stored in ...
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150 views

Calculating Joule heating in magnetic field

I have problem with calculating Joule heating in alternating magnetic field perpendicular through circulate plate with radios a and height h. Lets say that alternating magnetic field is in form of ...
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0answers
811 views

Calculate water use and design parameters for closed loop wet cooling tower

I am looking to estimate water use at a power plant with a closed loop wet cooling tower system. I have done some reading on cooling towers, but am struggling to connect the equations to a final ...
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0answers
95 views

How power affects heating of a coil

So I am doing a little research on my own about electronic cigarettes. Most Ecig users value high power at a standard current. This means they buy very expensive, high voltage batteries and put high ...
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0answers
44 views

Delivered/Reflected Power by Drive on a Hamiltonian System

Imagine a SHO with a drive F(t). (or in general a Hamiltonian system) What is the power delivered to the system and can we talk about the power reflected? is i am imagining say a MW oscillator ...
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0answers
32 views

Is it possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR?

I'd like to know if it is possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR (digital single lens reflex camera) mounted on tripod. Maybe, when shooting ...
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0answers
28 views

Rankine Cycle Reheat Mass Flow Rate

Having worked through many examples on the rankine cycle both non-reheat and reheat, i just have one question. Can the mass flow rate of steam be calculated given only the data below? Boiler ...
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0answers
16 views

power of an engine with wind

I know the power of an engine to overcome air drag is $1/2 c_d ρAv^3$. If the speed of the car $25\ \mathrm{m s}^{-1}$ (relative to the ground) and it travels in opposite direction to a wind at a ...
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0answers
22 views

how to calculate Cp of wind turbine

I am having trouble calculating C$_p$ of my wind turbine The radius of my rotor blade is 4.5 inches and it's rotation per second is 10 (10 rotations per second). So I found my tip speed of blade ...
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0answers
40 views

How is Thermal Design Power (TDP) related to Surface Power Density (SPD)

Although this question is kind of IT related I'm interested into the actual physical backgrounds and thus posting it here. I know that TDP is an indicator for dimension of the thermal dissipation ...
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0answers
38 views

Calculating electricity used for weights on an elevator

Given an elevator with a motor driven by a power supply, torque ability and a pulley does it take more electricity to lift more people? I have some of the calculations but do elevators lift at a set ...
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0answers
38 views

Forces in material removal (cutting, grinding, sanding, etc.)

A. Suppose a circular saw is spinning at a certain angular speed. When it starts to cut into the material, removing chips of the material or abrading it, the speed drops. The drop in speed depends on ...
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0answers
214 views

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 ...
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0answers
109 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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44 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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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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147 views

Determing aperture size for space-based-solar-power laser transmitter

I have hit a bit of a roadblock in my simulation. In the equation I require the aperture size for the laser source. $$I_a ≈ \frac{\lambda d}{A}$$ $I_a$ = aperture atop the atmosphere ($m$) $\lambda$...
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28 views

Power generated in Piezoelectric material

Good day everyone! I badly needed your help. I'm frustrated in plotting the power vs. frequency in piezoelectric material. Based on the equation: $$P = (I^2)R where $I$ is the current, and $R$ is ...